Vegetation Dynamics of the Uncompahgre Plateau
Landscape, Southwestern Colorado
William H. Romme
Department of Forest, Rangeland, and Watershed Stewardship, Colorado State
University, Fort Collins, CO 80523
Kevin McGarigal and David Goodwin
Department of Forestry and Wildlife Management, University of Massachusetts,
Amherst, MA01003
Draft Report, October 22, 2003
INTRODUCTION
The Uncompahgre Plateau is a large, prominent landform in southwestern Colorado,
which rises from the surrounding basins (ca. 1,500 m) to elevations as high as ca. 3,000
m. Local climate and vegetation change dramatically along this elevational gradient,
from desert scrub and grasslands in the semi-arid basins to spruce-fir and aspen forests at
the highest elevations. The Uncompahgre Plateau has provided important timber, forage,
and water resources, as well as recreation and aesthetics, to the inhabitants of western
Colorado for over a century. Looking to the future, a group of public land managers
representing the GMUG National Forest, the USDI Bureau of Land Management, the
Colorado Division of Wildlife, the Colorado State Forest Service, and others, are
partnering with private land owners and the public to develop a long-range vision for
sustainable management of the Uncompahgre Plateau. As a component of this planning
process, we have developed a dynamic landscape model (RMLANDS) that simulates
changes in landscape patterns under a range of natural and anthropogenic disturbance
regimes. The purpose of this report is two-fold: (1) to provide an overview of the
vegetation patterns and dynamics of the Uncompahgre Plateau for general planning
purposes, and (2) to provide the empirical basis for the parameters to be used in
RMLANDS simulations.
This report (and RMLANDS) devotes more attention to upland vegetation types than
to riparian or aquatic types; indeed, riparian and aquatic vegetation are covered only
briefly. There are two reasons for this emphasis on upland vegetation in RMLANDS: (1)
riparian and aquatic vegetation cover only a small (but ecologically critical!) portion of
the total Uncompahgre landscape, and (2) vegetation patterns and dynamics of riparian
and aquatic vegetation are more complex, more variable, and more difficult to model in a
straightforward fashion than are patterns and dynamics of upland vegetation. Additional
research is needed to fully characterize the range of variability in riparian and aquatic
ecosystems of the Uncompahgre region.
RMLANDS simulates vegetation change in the absence of major disturbance as a
sequence of successional stages following the model of Oliver (1981) and Oliver and
Larson (1990). Although this model has been criticized for its failure to incorporate the
1
full range of spatial and temporal variability in forest stand development (Franklin et al.
2002), we use it as a starting point in RMLANDS because it is widely recognized and
understood among ecologists and silviculturalists. We do modify the original Oliver
model to simulate the effects of differential fire mortality and alternative successional
trajectories, thus addressing some of the criticisms of Franklin et al. (2002). The Oliver
model consists of four successional stages following stand-replacing disturbance:
(i) stand initiation (SI), which entails recruitment of a new cohort of early
successional, shade-intolerant tree species into the open area created by the
disturbance
(ii) stem exclusion (SE), which occurs once the pioneer cohort has occupied all of
the open area and formed a closed canopy, thereby excluding further tree
recruitment because of intense competition for light and other resources
(iii) understory re-initiation, which begins when the pioneer cohort reaches
maturity and individual stems begin to die, creating gaps in the canopy into which
new stems can be recruited
(iv) shifting mosaic (SM) or old-growth, which begins when all or nearly all of
the pioneer cohort has died, and the stand becomes dominated by fine-scale gap
dynamics, which leads to great structural complexity
RMLANDS simulates both natural and anthropogenic disturbances. This report
focuses just on the effects of the two major natural disturbances in the Uncompahgre
region: fire and insects. Other kinds of natural disturbances also occur, including windthrow, ungulate and beaver herbivory, and soil movement, but the impacts of these other
disturbances tend to be localized in time or space, and have far less impact on vegetation
patterns over broad spatial and temporal scales than do fire and insects.
Effects of fire on vegetation are very diverse, depending on ambient weather
conditions, topography, vegetation characteristics at the time of the fire, and the pre-fire
history of the area (Whelan 1995, Brown et al. 2000). RMLANDS treats two levels of
fire mortality, expressed as the amount of plant mortality. High mortality fires are standreplacing disturbances that kill all or nearly all of the vegetation and return the stand to
the stand initiation or earliest successional stage of development. Low mortality fires kill
only a portion of the vegetation (typically smaller plants but not the dominant canopy
individuals) and may either accelerate the transition to a later stage of development or
serve to maintain the stand in its current condition. Vegetation types may be subjected to
high mortality or low mortality fire and RMLANDS incorporates both types of fires in a
stochastic manner.
Hundreds of species of insects, fungi, and other agents of tree death or damage
inhabit western forests (Furniss and Carolin 1977). Any of them may be locally important
on occasion. However, it is not feasible to explicitly simulate more than a handful of
insects and diseases in a complex landscape model like RMLANDS. Therefore, we
identified four insect species and one insect/disease (pathogen) complex that have the
most frequent and widespread impact on vegetation in the Uncompahgre region. The
insects include mountain pine beetle (Dendroctonus ponderosae), Douglas-fir bark beetle
(Dendroctonus pseudotsugae), spruce bark beetle (Dendroctonus rufipennis), and western
spruce budworm (Choristoneura occidentalis). The three beetles are bark beetles that kill
2
living trees; the budworm is a defoliator that generally does not kill trees directly but
weakens them, makes the trees more susceptible to subsequent beetle attack; the
budworm may eventually kill trees if the defoliation continues for a long time. Life
histories and ecological impacts of these insects are summarized by Furnis and Carolin
(1977). The insect/disease complex that we treat is referred to as “pinyon decline.”
Black stain root rot (Verticicladiella wagneri) kills or weakens pinyon trees, which then
become more susceptible to attack by the pinyon ips beetle (Ips confusus). Pinyon ips
also kills pinyon trees directly, without previous infection by black stain root rot,
especially if trees are weakened by drought or soil disturbance (Furniss and Carolin
1977). Both kill pinyon only, leaving the juniper, shrub, and herbaceous components
intact. The presence of human activity, especially new home construction (in which slash
piles of Pinus edulis and Juniperus osteosperma are created or when Pinus edulis and
Juniperus osteosperma are moved for landscaping) greatly accelerates the spread of
pinyon decline.
Vegetation can be classified in a great many ways, each classification system being
most useful in a particular context. The vegetation of the Uncompahgre region has been
previously classified both in very general ways (e.g., Daubenmire 1945, Costello 1954,
Bailey 1995) and in great detail (e.g., Johnston and Huckaby 2001). No previous
classification system was entirely suitable for the purposes of RMLANDS, however, so
we developed a new system tailored to the needs and capabilities of RMLANDS. This
new classification was based initially on our own field observations and experience in
southwestern Colorado, and then was revised and improved by discussions with land
managers who work in the Uncompahgre area. We recognize 23 distinct vegetation types
(“cover types”) in the Uncompahgre study area for the purposes of RMLANDS
simulations (plus “Roads”, “Agriculture” and “Urban” which are needed as a cover type
for simulation purposes, but obviously do not represent a vegetation type). The
remainder of this report summarizes, for each cover type, its general distribution on the
Uncompahgre Plateau, vegetation structure and composition, stand conditions and
successional trends, effects of natural disturbances, and reference conditions and 20th
century changes. For cover types that undergo successional processes, the section
concludes with a summary model of successional stages and dynamics, as simulated in
RMLANDS. We provide much greater detail on vegetation patterns, dynamics, and 20th
century changes for most of these cover types in a companion report on the South Central
Highlands Section, which includes the Uncompahgre Plateau (Romme et al. 2003).
In the following narrative that describes how stands follow normal successional
pathways and retrogressive pathways following disturbances, we make a distinction
between processes that “recycle” a stand in its current condition and those that
“maintain” a stand in its current condition. We use “recycle” to imply that a disturbance
has caused the stand’s condition age to be reset to zero while we use “maintain” to imply
that a disturbance has occurred but has not reset the stand’s condition age. This is an
important distinction as it will have an impact on how stands will be affected by
successional probabilities following a disturbance. Generally, stands that are
“maintained” will be older and therefore succeed quicker than stands that are “recycled”.
3
TABLE 1. VEGETATION (“COVER TYPES’) OF
THE UNCOMPAHGRE PLATEAU, AS USED IN RMLANDS
1. Roads
2. Barren
3. Water
4. Meadows
5. Riparian
6. Greasewood
7. Semi-Desert Grassland
8. Semi-Desert Savannah
9. Sparse Pinyon-Juniper Woodland
10. Pinyon-Juniper Woodland
11. Pinyon-Juniper-Sagebrush
12. Pinyon-Juniper-Oak-Serviceberry
13. Oak-Serviceberry Shrubland
14. Ponderosa Pine–Oak Forest
15. Ponderosa Pine–Oak–Aspen Forest
16. Warm-Dry Mixed-Conifer Forest
17. Warm-Dry Mixed-Conifer with Aspen Forest
18. Cool-Moist Mixed-Conifer Forest
19. Cool-Moist Mixed-Conifer with Aspen Forest
20. Pure Aspen Forest
21. Spruce-Fir Forest
22. Spruce-Fir – Aspen Forest
23. Spruce Forest
24. High-Elevation Sagebrush
98. Agriculture
99. Urban
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1. Roads
This is a “cover type” in RMLANDS, but obviously is not a type of vegetation.
2. Barren
Distribution.
This type is scattered throughout the Uncompahgre region at all elevations, but is
especially common at lower elevations, especially on “slickrock” or outcrops of marine
shales. Similar communities are found throughout the Colorado Plateau region (West
1983, 1988; Heil et al. 1993, Romme et al. 1993).
Vegetation Structure & Composition.
This cover type is characterized by a paucity or absence of vegetation cover. The
substrate may be bedrock or unstable colluvium or highly erosive bedrock at any
elevation, salt-rich shale at low elevations (“salt-desert shrublands” sensu West 1983), or
may be persistent snow or ice. Often a few plants can be found, e.g., scattered Juniperus
osteosperma or Atriplex confertifolia or cushion-forming herbs at low elevations, or low
shrubs and cushion-forming herbs at high elevations. Soil fertility and decomposition
rates generally are greatest in the immediate vicinity of the shrubs (West 1983).
Stand Conditions and Successional Trends.
Barren areas do not appear to undergo any obvious pattern of succession.
Effects of Natural Disturbances.
Disturbances do not appear to have an important impact on the few plants and
animals that live in this environment. In particular, wildfire probably is extremely
infrequent because of lack of fuels.
Reference Conditions and 20th Century Changes.
We find no evidence that this cover type has changed significantly in the last century;
hence, reference conditions are regarded as essentially the same as current conditions in
most areas.
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3. Water
Distribution.
This cover type is found at all elevations throughout the Uncompahgre region.
Vegetation Structure & Composition.
Either standing or flowing water may be represented in this cover type. There is a
small vegetation component in some places, e.g., emergent Typha latifolia or floating
Ranunculus aquaticus or Nuphar luteum
Stand Conditions and Successional Trends.
Although succession does occur in aquatic ecosystems, we do not treat aquatic
succession in our modeling work (RMLANDS).
Effects of Natural Disturbances.
Disturbance by wildfire, insect/pathogens, or animals generally are not important in
streams and ponds of the Uncompahgre region, and are not treated in our modeling work
(RMLANDS).
Reference Conditions and 20th Century Changes.
Although local conditions do fluctuate over time in aquatic ecosystems, we are not
aware of systematic changes in the vegetation component of streams and ponds in the
Uncompahgre region, and assume therefore that this cover type has not changed
significantly in composition or structure during the last 125 years the last century.
6
4. Meadow
Distribution.
This cover type is found at all elevations throughout the Uncompahgre region.
Similar communities are found throughout the Colorado Plateau and southern Rocky
Mountain regions (Johnston and Huckaby 2001).
Vegetation Structure & Composition.
Meadows are characterized by an absence or very low cover of trees and shrubs, and
dominance by grasses and forbs. They commonly exist as openings within forests of
ponderosa pine, mixed conifers, aspen, or spruce-fir. The lack of trees may be due to a
variety of mechanisms, including competition from herbaceous plants, temperatures,
grazing, soil heaving, and fire (Paulsen 1975). Low-elevation meadows generally are
associated with valley bottoms where natural springs or human irrigation provide
supplemental moisture. High-elevation meadows, sometimes called parks, are found in
all topographic settings, but are somewhat more common on relatively dry settings such
as ridgetops or south-facing slopes. Physiognomy of meadows is similar to that of semiarid grasslands (below), but in our classification meadows generally are on more mesic
sites than semi-arid grasslands, often in association with forests of various composition.
Species composition changes substantially with soil conditions, and grazing history
(Redders 2003a). Dominant species on relatively dry sites at low to mid elevations (ca.
2286 to 2743 meters) may include Festuca arizonica, Poa pratensis, Artemisia frigida ,
Wyethia amplexicaulis, Fragaria vesca, Fragaria virginiana, Antennaria rosea,
Geranium caespitosum, and Achillea millefolium. Dominant species on relatively dry
sites at mid to high elevations ( > ca. 2591 meters) may include Festuca thurberi, Poa
pratensis, Campanula rotundifolia, Pseudocymopterus montanus, Thalictrum fendleri,
and Dugaldia hoopesii. In many places, meadows have been seeded with non-native
species to increase livestock forage production. In these areas, common species include
Bromopsis inermis, Thinopyrum intermedium, Phleum pratense, Agropyron cristatum,
and Dactylis glomrata.
Stand Conditions and Successional Trends.
We do not simulate disturbance and succession in this cover type in our modeling
work (RMLANDS) because of its relatively small extent. However, meadows are subject
to disturbance by fire and animals (e.g., prairie dogs and pocket gophers), as described
below for semi-desert grassland. Many of the meadows in the Uncompahgre region also
have been dramatically altered during the last 100 years by heavy grazing, plowing, and
planting of non-native species, as described in the next section.
Effects of Natural Disturbances.
Wildfire. Fires historically burned meadows and grasslands, but fire intervals during
the reference period are poorly known. Generally, fire intervals in grasslands probably
were similar to intervals in adjacent forest types. We find no evidence that meadows
burned independently of adjacent forests and shrublands; on the contrary, fires probably
spread from forests of shrublands into nearly meadows or from the meadows into
adjacent woody vegetation. The effects of fire on meadows and grasslands usually are
7
transient; when modeled over a 10 year time step (RMLANDS) fire does not alter
vegetation structure or composition. This is because the fire may consume above-ground
plant parts, but below-ground structures survive and re-sprout promptly. Seedling
establishment also occurs where the fire removes litter and plant cover, but the
prevalence of post-fire sprouting usually leads to rapid (< 10 years) restoration of pre-fire
structure with little change in composition. Thus, within the framework of the 10-year
time step employed in RMLANDS, fire in grasslands occurs but does not initiate a
successional sequence.
Reference Conditions and 20th Century Changes.
Species composition of many or most Rocky Mountain meadows and grasslands
is thought to have been altered substantially by the heavy livestock grazing that occurred
in the late 1800s and early 1900s (Fleischner 1994, Belsky and Blumenthal 1997).
Heavy, unregulated grazing begin in the Uncompahgre region in the 1880s (Rockwell
1999), and continued into the 20th century. Since the the passage of the Taylor Grazing
Act in 1934, livestock grazing has been regulated on public lands, and rangeland
conditions generally have improved, but we still have legacies of the previously
uncontrolled livestock grazing.
Grassland composition was not well documented before the onset of grazing, so much
of our interpretation is based on inference and informed speculation. A handful of
studies documented floristic changes as grazing intensity increased during the early 20th
century (Arnold 1950) or compared grazed and ungrazed areas that were otherwise
similar (Rummell (1951, Madany and West 1983). These studies show that heavy,
sustained cattle and sheep grazing reduced the cover of the more palatable herbaceous
species (e.g., Festuca arizonica, Muhlenbergia montana), and even extirpated them from
local sites. Invasive non-native species (e.g., Poa pratensis, Taraxicum officinale) and
native increaser species (e.g., Wyethia amplexicaulis, Dugaldia hoopesii. Achillea
millefolium) have replaced the formerly dominant bunchgrasses in many places (Mullen
1992, Redders 2003a). Despite the compositional changes, however, the overall
structure of these plant communities today apparently remains similar to the pre-1900
state. See Redders (2003a) for a more thorough discussion of meadows and grasslands in
the South Central Highlands Section that includes the San Juan Mountains and
Uncompahgre Plateau.
8
5. Riparian
Distribution.
This cover type is found at all elevations throughout the Uncompahgre region, along
streams and pond margins, and other locations where moisture is available perennially
near the soil surface. Similar communities are found throughout the Colorado Plateau
and southern Rocky Mountain regions (Somers and Floyd-Hanna 1996, Johnston and
Huckaby 2001).
Structure & Composition.
Riparian vegetation structure and species composition are extremely variable at
multiple scales, from broad-scale elevational gradients to very fine-scale patterns related
to local variation in soil moisture, organic matter, and light conditions (Redders 2003b).
At the broad scale, dominant woody species vary from Populus wislizenii and Salix
exigua at low elevations, to Populus angustifolia and Alnus tenuifolia at middle
elevations, to Salix drummondiana and Salix geyeriana at the highest elevations.
Common herbaceous species at lower to mid elevations include Juncus balticus, Phalaris
arundinacea, Typha latifolia, Heracleum lanatum,and Galium triflorum. Common
herbaceous species at mid to higher elevations include Deschampsia cespitosa, Carex
aquatilis, Mertensia ciliate, Pedicularis groenlandica, Cardamine cordifolia, Geranium
richardsonii, Fragaria virginiana, and Senecio triangularis at high elevations (species
list from Jeff Redders, San Juan National Forest, and personal observations).
Riparian vegetation is extremely variable in structure and composition, and it is
beyond the scope of this report to characterize all of the interesting variation. Because
the riparian cover type usually comprises only a narrow strip of vegetation along a
perennial water source, and because structure and composition are so variable, we treat
riparian vegetation as a single cover type for modeling purposes (RMLANDS). See
Redders (2003b) for a more detailed treatment of riparian vegetation in the South Central
Highlands Section, which includes the San Juan Mountains and Uncompahgre Plateau.
Stand Conditions and Successional Trends.
We do not simulate disturbance and succession in this cover type in our modeling
work (RMLANDS) because of its relatively small extent. However, riparian areas are
subject to disturbance by fire and animals. Many of the riparian areas in the
Uncompahgre region also have been dramatically altered during the last 100 years by
heavy grazing, plowing, planting of non-native species, and invasion of non-native
species (e.g., Tamarix chinensis and Cirsium arvense).
Effects of Natural Disturbances.
Natural disturbances do occur in riparian areas, e.g., fire, flooding, and heavy grazing
or browsing. However, we do not treat disturbances in riparian areas in our modeling
work (RMLANDS). This is because the riparian zone is generally very narrow, highly
variable structure and composition, and subject to diverse post-disturbance successional
trajectories. Attempting to incorporate all of this fine-scale variability into a landscape
model like RMLANDS would likely obscure the broad-scale patterns that we are seeking,
and so we treat riparian vegetation as a single cover type.
9
Reference Conditions and 20th Century Changes.
The structure and composition of many riparian communities probably has changed
significantly during the last century because of livestock grazing, temporary or persistent
loss of beaver, invasion of non-native species, and diversion of water (Redders 2003b).
However, as with the meadow cover type, reference conditions in riparian vegetation are
poorly documented, and the changes since the reference period are therefore difficult to
quantify. From a broad perspective, species composition and structural diversity
probably remain similar to the reference state (i.e., no species have been entirely
extirpated and at least some examples of all original structural types can still be found),
but local conditions have been profoundly changed in many locations. Because
RMLANDS treats all riparian vegetation as a single cover type, we do not attempt to deal
with local variation or changes since the reference period. See Redders (2003b) for a
more detailed treatment of riparian vegetation in the South Central Highlands Section,
which includes the San Juan Mountains and Uncompahgre Plateau.
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6. Greasewood
Distribution.
This cover type is scattered throughout the Uncompahgre region at lower elevations,
usually in flat or gently sloping sites where seasonal flooding or inherently saline
substrates result in relatively high soil salt content. Soil moisture usually is available
within 1 m of the soil surface (West 1988). Similar communities are found throughout
the Colorado Plateau region (West 1983, 1988; Heil et al. 1993, Romme et al. 1993).
Structure & Composition.
The shrub Sarcobatus vermiculatus dominates stands, with a sparse to well-developed
herbaceous stratum that may include Sporobolus airoides and other salt-tolerant grasses
and forbs. Other shrubs, including Atriplex canescens and Chrysothamnus nauseosus,
also may be present. Recently burned stands have a greater herbaceous component; longunburned or heavily grazed stands may support a nearly continuous shrub layer with little
herbaceous vegetation.
Stand Conditions and Successional Trends.
We do not simulate disturbance and succession in this cover type in our modeling
work (RMLANDS) because of its relatively small extent and the rapidity with which it
usually recovers following disturbance (see below).
Effects of Natural Disturbances.
Wildfire. Fires historically burned greasewood communities, but fire intervals during
the reference period are poorly known. The effects of fire in this cover type appear to be
relatively transient; when modeled over a 10 year time step (RMLANDS) fire does not
alter vegetation structure or composition. This is because the fire may kill or consume
above-ground plant parts, but below-ground structures survive and re-sprout promptly.
Seedling establishment also occurs where the fire removes litter and plant cover. The
combination of post-fire re-sprouting and seedling establishment usually leads to rapid (<
10 years) restoration of pre-fire structure with little change in composition. Thus, within
the framework of the 10-year time step employed in RMLANDS, fire in greasewood
communities occurs but does not initiate a successional sequence.
Reference Conditions and 20th Century Changes.
Reference conditions in this cover type are essentially unknown, but presumably were
similar in overall structure and composition to current conditions.
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7. Semi-Desert Grassland
Distribution.
Semi-desert grasslands are found at the lowest elevations, primarily on the east side
of the Uncompahgre Plateau, and most commonly on relatively fine-textured soils
derived from Morrison shale and Dakota sandstone on the lower slopes of large canyons.
Similar communities are found throughout the Colorado Plateau region (Loope 1977,
West 1983, 1988; Heil et al. 1993, Romme et al. 1993).
Structure & Composition.
Semi-desert grasslands support a sparse cover of low shrubs, grasses, and forbs, with
much bare ground. Dominant species include the low shrubs Atriplex confertifolia,
Eurotia lanata, and Chrysothamnus viscidiflorus, plus the cool-season grasses Stipa
comata and Oryzopsis hymenoides, and the warm-season grasses Hilaria jamesii and
Bouteloua gracilis. Species composition varies from place to place with local differences
in soil conditions and disturbance history. Chronically disturbed areas may be dominated
by the native increasers Opuntia polyacantha and Gutierrezia sarothrae, or by the
invasive non-native annual grass Bromus tectorum.
Stand Conditions and Successional Trends.
Disturbance by fire or prairie dogs initiates a successional sequence in which three
major stages can be recognized:
·
·
·
Early Grass - Forb (EGF), herbaceous species dominant, with a mix of annuals
and perennials … persists from stand age 0 until age 20-30
Mid Grass - Shrub (MGS), herbaceous dominant, mostly perennials, with some
shrubs becoming established … persists from stand age 20-30 until age 50-70
Shrub Dominated (SD), a mix of mature shrubs and perennial herbs … persists
from stand age 50-70 until the next stand-replacing disturbance
Effects of Natural Disturbances.
Wildfire. Fire kills the shrubs, most of which must re-establish from seed.
Herbaceous plants lose above-ground biomass to fire, but most promptly re-sprout from
surviving below-ground organs.
·
·
·
Early Grass – Forb (EGF), a high mortality wildfire recycles the stand in this
early successional condition while a low mortality wildfire maintains the
condition
Mid Grass - Shrub (MGS), high mortality wildfire returns the stand to EGF
while low mortality wildfire maintains this mid successional condition
Shrub Dominated (SD), high mortality wildfire returns the stand to EGF while a
low mortality wildfire either sends the stand back to MGS or maintains the stand
in this late successional condition
Prairie dogs. Prairie dogs inhabit many western grasslands, and may be a key
disturbance agent in these ecosystems. These rodents not only feed on grass, but
typically remove all vegetation from the vicinity of their extensive burrows or “towns” in
12
order to detect predators. As long as a prairie dog town is active, the animals will
intensively remove all vegetation and maintain the area at the beginning of the earliest
successional stage (EFG), but when they abandon a site, the successional sequence
proceeds eventually to the final shrub-dominated stage. Selective feeding by prairie dogs
around the periphery of the town may remove grasses but not shrubs, thus hastening
development of the final shrub-dominated successional stage.
·
·
·
Early Grass – Forb (EGF), high mortality prairie dog activity will recycle the
stand in this early successional condition while low mortality activity can either
accelerate the stand all the way up to SD if grasses and herbs are disturbed
enough leaving primarily shrubs as the dominant life form or maintain the stand
in this early successional condition
Mid Grass - Shrub (MGS), high mortality prairie dog activity will return the
stand back to EGF while low mortality prairie dog activity will either maintain the
stand in this mid successional condition or accelerate the stand up to SD
Shrub Dominated (SD), high or low mortality prairie dog activity will maintain
the stand within this late successional condition
Reference Conditions and 20th Century Changes.
Species composition of most southwestern grasslands is thought to have been altered
substantially by the heavy livestock grazing that occurred in the late 1800s and early
1900s, as discussed above under the Meadows cover type. Thus, many grasslands that
today are dominated by grazing-tolerant species may have had a substantially different
composition 150 years ago. Although it is difficult to reconstruct pre-1880 species
composition in this vegetation type, where nearly every stand has been heavily grazed, it
is thought that the perennial grasses (e.g., Stipa comata, Bouteloua gracilis and Hilaria
jamesii) were generally dominant in most areas (Heil et al. 1993, Romme et al. 1993).
Despite the compositional changes of the last 100 years, however, the overall structure of
these plant communities today apparently remains similar to the pre-1900 state. See
Redders (2003a) for a more thorough discussion of meadows and grasslands in the South
Central Highlands Section that includes the San Juan Mountains and Uncompahgre
Plateau.
RMLANDS State Transition Diagram for Semi-Desert Grasslands
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8. Semi-Desert Savannah
Distribution.
Semi-Desert Savannah is found on very dry sites at the lowest elevations, primarily
on the east side of the Uncompahgre Plateau, commonly on gently sloping ridges of
Dakota sandstone lying between major canyons. Similar communities are found
throughout the Colorado Plateau region (Loope 1977, West 1983, 1988; Heil et al. 1993,
Romme et al. 1993).
Structure & Composition.
Savannah vegetation consists of scattered trees within a grassland matrix. This cover
type is found on very dry sites that lack sufficient moisture to support a true woodland or
shrubland vegetation type. Stands are composed of scattered small Pinus edulis and
Juniperus osteosperma, and a moderately dense cover of shrubs (Atriplex confertifolia,
Artemisia biglovii, Eurotia lanata, Chrysothamnus viscidiflorus) and grasses (Hilaria
jamesii, Bouteloua gracilis, Stipa comata).
Stand Conditions and Successional Trends.
Recovery of the tree component after intense disturbance is very slow, because of the
dry conditions. The herbaceous component responds to disturbance much like the semidesert grassland cover type described above.
·
·
·
Herb - Annual (HA) – herbaceous annuals … persists from stand age 0 until 10
Herb – Perennial (HP) – herbaceous perennials … persists from stand age 10
until age 20-30
Herb – Shrub - Trees (HST) – herbaceous perennial, sparse density of older
Pinus edulis, Juniperus osteosperma, moderate to dense shrubs, grasses, and forbs
… persists from stand age 20-30 until the next stand-replacing disturbance
Effects of Natural Disturbances.
Wildfire. wildfire is rare because of low fuel mass and continuity. When fire does
occur, it kills the trees and shrubs, most of which must re-establish from seed.
Herbaceous plants lose above-ground biomass to fire, but most promptly re-sprout from
surviving below-ground organs.
·
·
·
Herb - Annual (HA) – wildfire is generally high mortality and recycles the stand
in this early successional condition but a low mortality wildfire will maintain this
condition
Herb – Perennial (HP) – high mortality wildfire returns stand to the HA
condition while a low mortality wildfire maintains the stand in this mid
successional condition
Herb – Shrub - Trees (HST) – high mortality wildfire returns stand to the HA
condition while a low mortality wildfire maintains the stand in this late
successional condition
Reference Conditions and 20th Century Changes.
14
Reference conditions in this cover type are basically unknown, but vegetation
structure and composition probably were similar to conditions today.
RMLANDS State Transition Diagram for Semi-Desert Savannah
15
9. Sparse Pinyon-Juniper Woodland
Distribution.
This cover type is found on steep or unstable slopes, usually of exposed sandstone
bedrock (“slickrock”) or erosive shale or colluvium, under dry conditions at lower
elevations. Similar communities are found throughout the Colorado Plateau region
(Loope 1977, West 1983, 1988; Heil et al. 1993, Romme et al. 1993).
Structure & Composition.
The combination of low precipitation and unfavorable substrate results in a very
sparse herbaceous component, but a scattering of trees and shrubs can survive the harsh
growing conditions. Major species include Juniperus osteosperma and Pinus edulis, with
Cercocarpus inticatus, Fraxinus anomala, Artemisia biglovii and other shrubs in places.
This cover type is similar to the semi-desert savannah discussed above, in that both
support a sparse woodland of pinyon and juniper, but the sparse pinyon-juniper cover
type lacks the well-developed herbaceous component found in the semi-desert savannah.
Stand Conditions and Successional Trends
We do not simulate disturbance and succession in this cover type in our modeling
work (RMLANDS) because disturbance appears very infrequent, and no successional
trends are apparent.
·
No Conditions (NC) – we do not recognize separate stand conditions in this
cover type
Effects of Natural Disturbances.
Wildfire. Fires tend to be very infrequent because of lack of fuel continuity. Pinyon
decline can cause mortality of Pinus edulis. However, since there is only one condition
recognized in RMLANDS, disturbances either recycle within this single condition or
maintain the condition.
·
No Conditions (NC) – high mortality fire recycles the stand within this condition
while a low mortality fire maintains the condition
Insects/Pathogens. Pinyon decline (combination of black stain root fungus and
engraver bark beetles) kills pinyon trees of all sizes, but does not directly affect junipers,
shrubs, or herbs.
·
No Conditions (NC) – high or low mortality pinyon decline maintain the
condition
Reference Conditions and 20th Century Changes.
Reference conditions are essentially unknown, but structure and composition
probably were similar to current conditions.
RMLANDS State Transition Diagram for Sparse Pinyon-Juniper Woodland
16
17
10. Pinyon-Juniper Woodland
Distribution.
Pinyon-Juniper Woodland is a widespread cover type at lower to middle elevations on
both sides of the Uncompahgre Plateau, especially on sandstone substrates. Similar
communities are found throughout the Colorado Plateau and southern Rocky Mountain
regions (Loope 1977, West 1983, 1988; Peet 1988, Heil et al. 1993, Romme et al. 1993,
Floyd-Hanna et al. 1996).
Structure & Composition.
This cover type consists of sparse to dense stands of Pinus edulis and Juniperus
osteosperma, with a variable understory of low shrub species such as Purshia tridentata,
Ephedra viridis, and Artemisa nova. Herb cover is highly variable, and may include the
cool-season grasses Poa fendleriana, Poa secunda, Agropyron smithii, the warm-season
grasses Hilaria jamesii, Bouteloua gracilis, Sitanion hystrix, and Oryzopsis hymenoides,
and the forbs Heterotheca villosa and Penstemon linarioides. Juniper tends to be more
abundant at the lower elevations, pinyon tends to be more abundant at the higher
elevations, and the two species share dominance within a broad middle-elevation zone
(Woodin and Lindsey 1954, Heil et al. 1993). At the highest elevations, Juniperus
osteosperma may be replaced by Juniperus scopulorum. Tree density also tends to
increase with elevation, due to greater precipitation and reduced evapotranspiration at the
higher elevations (Spencer and Romme 1996).
Stand Conditions and Successional Trends.
·
·
·
·
Herb Dominated (HD) – This is the initial successional stage following a severe
disturbance. Stands are dominated by a mixture of short-lived native herbaceous
species, including Chenopodium fremontii and the fire-dependent Nicotiana
attenuata, as well as re-sprouting native grasses including Hilaria jamesii and
Bouteloua gracilis. Non-native annuals and biennials such as Bromus tectorum,
Lactuca serriola, and Alyssum minor may dominate in highly disturbed sites …
persists from stand age 0 until age 10
Herbs - Shrubs (HS) – Within one to several decades after a severe disturbance,
shrub seedlings become established and co-dominate with the early successional
herbs which are still abundant … persists from stand age 10 until age 50-70
Shrubs - Trees (ST) – The low shrubs dominate the stand, though the grasses
and perennial forbs of earlier successional stages are still well represented, and
young Pinus edulis and Juniperus osteosperma are poking through the shrub
canopy … persists from stand age 50-70 until age 150-200
Tree Dominated (TD) – The stand is dominated by a mature canopy of Pinus
edulis and Juniperus osteosperma. The low shrubs and perennial herbs are still
present, but have reduced cover if tree cover is high … persists from stand age
150-200 until the next stand-replacing disturbance
Effects of Natural Disturbances.
18
Wildfire. Fire kills the trees and shrubs, most of which must re-establish from seed.
Herbaceous plants lose above-ground biomass to fire, but most promptly re-sprout from
surviving below-ground organs.
·
·
·
·
Herb Dominated (HD)– high mortality wildfire recycles the stand in this early
successional condition while a low mortality wildfire maintains this condition
Herbs - Shrubs (HS)– high mortality wildfires send the stand back to the HD
condition while a low mortality wildfire maintains the stand in this successional
condition
Shrubs - Trees (ST)– high mortality wildfires send the stand back to the HD
condition while a low mortality wildfire maintains the stand in this successional
condition
Tree Dominated (TD) – high mortality wildfires send the stand back to the HD
condition while a low mortality wildfire maintains the stand in this successional
condition
Insects/Pathogens. Pinyon decline (combination of black stain root fungus and
engraver bark beetles) kills pinyon trees of all sizes, but does not directly affect junipers,
shrubs, or herbs.
·
·
·
·
Herb Dominated (HD) –not susceptible to black stain or beetles
Herbs - Shrubs (HS) – high or low mortality pinyon decline maintains the HS
stage because the juniper component survives the outbreak, after which the stand
resumes its usual successional trajectory
Shrubs - Trees (ST) – either high or low mortality pinyon decline returns an
affected stand to the HS stage
Tree Dominated (TD) – high mortality pinyon decline returns the stand to the HS
condition while low mortality pinyon decline returns the stand to the ST condition
Reference Conditions and 20th Century Changes.
Prior to Euro-American settlement in the late 1800s, the pinyon-juniper landscape
was composed of a mosaic of stands in different stages of succession following earlier
disturbances. We have no specific information about proportions of successional stages
or patch sizes and shapes in the reference landscape. Proportions and patch sizes
probably fluctuated over time, with more and larger patches of early successional stages
during dry periods with greater fire frequency, and a greater preponderance of late
successional stages during wet periods with reduced fire frequency. Although
proportions fluctuated with climatic fluctuation, at a broad scale probably every stage
was always represented somewhere in the landscape. See chapter 6 in Romme et al.
(2003) for a discussion of pinyon-juniper forests in the South Central Highlands Section
which includes the Uncompahgre Plateau.
RMLANDS State Transition Diagram for Pinyon-Juniper Woodland
19
20
11. Pinyon-Juniper-Sagebrush Woodland
Distribution.
Pinyon-Juniper-Sagebrush Woodland is widespread on both sides of the
Uncompahgre Plateau at lower to middle elevations, especially on relatively deep soils
developing from sandstone substrates. Artemisia tridentata is intolerant of high soil
salinity (West 1983, 1988). Similar communities are found throughout the Colorado
Plateau and southern Rocky Mountain regions (Loope 1977, West 1983, 1988; Heil et al.
1993, Romme et al. 1993)
Structure & Composition.
This cover type consists of sparse to dense stands of Pinus edulis and Juniperus
osteosperma, with a sparse to dense understory of Artemisia tridentata, grasses (Poa
secunda, Agropyron smithii, Hilaria jamesii, Bouteloua gracilis, Sitanion hystrix,
Oryzopsis hymenoides, Agropyron cristatum ), and forbs (e.g., Heterotheca villosa,
Penstemon linarioides).
Stand Conditions and Successional Trends.
·
·
·
·
Herb Dominated (HD)– This is the initial successional stage following a severe
disturbance. Stands are dominated by a mixture of short-lived native herbaceous
species, including Chenopodium fremontii and the fire-dependent Nicotiana
attenuata, as well as re-sprouting native grasses and forbs including Hilaria
jamesii, Bouteloua gracilis and Penstemon linarioides. Non-native annuals and
biennials such as Bromus tectorum, Lactuca serriola, and Alyssum minor may
dominate in highly disturbed sites … persists from stand age 0 until age 10
Herbs - Shrubs (HS)– Within approximately a decade after a severe
disturbance, Artemisia tridentata seedlings become established and co-dominate
with the early successional herbs which are still abundant … persists from stand
age 10 until age 50-70
Shrubs - Trees (ST)– Artemisia tridentata dominates the stand, often with 50%
or more total cover. Herb cover is greatly diminished, though the grasses and
perennial forbs of earlier successional stages are still present, and young Pinus
edulis and Juniperus osteosperma are poking through the sagebrush canopy …
persists from stand age 50-70 until age 150-200
Tree Dominated (TD) – The stand is dominated by a mature and often dense
canopy of Pinus edulis and Juniperus osteosperma. Sagebrush and perennial
herbs are still present, but have low total cover … persists from stand age 150-200
until the next stand-replacing disturbance
Effects of Natural Disturbances.
Wildfire. Fire kills the trees and shrubs, most of which must re-establish from seed.
Herbaceous plants lose above-ground biomass to fire, but most promptly re-sprout from
surviving below-ground organs.
·
Herb Dominated (HD)– high mortality wildfire recycles the stand in this early
successional condition while a low mortality wildfire maintains this condition
21
·
·
·
Herbs - Shrubs (HS)– high mortality wildfires send the stand back to the HD
condition while a low mortality wildfire maintains the stand in this successional
condition
Shrubs - Trees (ST)– high mortality wildfires send the stand back to the HD
condition while a low mortality wildfire maintains the stand in this successional
condition
Tree Dominated (TD) – high mortality wildfires send the stand back to the HD
condition while a low mortality wildfire maintains the stand in this successional
condition
Insects/Pathogens. Pinyon decline (combination of black stain root fungus and
engraver bark beetles) kills pinyon trees of all sizes, but does not directly affect junipers,
shrubs, or herbs.
·
·
·
·
Herb Dominated (HD) –not susceptible to black stain or beetles
Herbs - Shrubs (HS) – high or low mortality pinyon decline maintains the HS
stage because the juniper component survives the outbreak, after which the stand
resumes its usual successional trajectory
Shrubs - Trees (ST) – either high or low mortality pinyon decline returns an
affected stand to the HS stage
Tree Dominated (TD) – high mortality pinyon decline returns the stand to the HS
condition while low mortality pinyon decline returns the stand to the ST condition
Reference Conditions and 20th Century Changes.
Prior to Euro-American settlement in the late 1800s, the pinyon-juniper landscape
was composed of a mosaic of stands in different stages of succession following earlier
disturbances. We have no specific information about proportions of successional stages
or patch sizes and shapes in the reference landscape. Proportions and patch sizes
probably fluctuated over time, with more and larger patches of early successional stages
during dry periods with greater fire frequency, and a greater preponderance of late
successional stages during wet periods with reduced fire frequency. Although
proportions fluctuated with climatic fluctuation, at a broad scale probably every stage
was always represented somewhere in the landscape. See chapter 6-A in Romme et al.
(2003) for a discussion of pinyon-juniper forests in the South Central Highlands Section
which includes the Uncompahgre Plateau.
RMLANDS State Transition Diagram for Pinyon-Juniper-Sagebrush Woodland
22
23
12. Pinyon-Juniper-Oak-Serviceberry Woodland
Distribution.
This widespread cover type is found at middle to high elevations on both sides of the
plateau, often on sandstone substrates. Similar communities are found in many parts of
western Colorado (Floyd et al. 2000, Spencer et al. 1996).
Structure & Composition.
Pinyon-Juniper-Oak-Serviceberry consists of sparse to dense stands of Pinus edulis
and Juniperus osteosperma, with a sparse to dense understory of Quercus gambelii,
Amelanchier utahensis, and sometimes also Symphoricarpos spp., or Purshia tridentata.
Grasses, notably Poa fendleriana , and forbs, e.g., Wyethia amplexicaulis, Lupinus spp.,
Lathyrus pauciflorus, Lathyrus leucanthus, Penstemon linarioides, and Delphinium
nelsoni, also are present, forming a sometimes dense ground layer.
Stand Conditions and Successional Trends.
·
·
·
·
Herb Dominated (HD)– This is the initial successional stage following a severe
disturbance. Stands are dominated by a mixture of short-lived native herbaceous
species, including Chenopodium fremontii and the fire-dependent Nicotiana
attenuata, as well as re-sprouting native grasses and forbs including Poa
fendleriana and Wyethia amplexicaulis. Non-native annuals and biennials such as
Bromus tectorum, Lactuca serriola, and Alyssum minor may dominate in highly
disturbed sites … persists from stand age 0 until age 10
Herbs - Shrubs (HS)– Within the first decade after a severe disturbance, the
dominant shrubs re-sprout and form a dense cover of low shrubs. The early
successional herbs are also present and have high cover … persists from stand age
10 until age 50-70
Shrubs - Trees (ST)– The shrubs dominate the stand, often with 50% or more
total cover. Herb cover is greatly diminished, though the grasses and perennial
forbs of earlier successional stages are still present, and young Pinus edulis and
Juniperus osteosperma are poking through the shrub canopy … persists from
stand age 50-70 until age 150-200
Tree Dominated (TD) – The stand is dominated by a mature and often dense
canopy of Pinus edulis and Juniperus osteosperma. The shrubs and perennial
herbs are still present, but have low total cover … persists from stand age 150-200
until the next stand-replacing disturbance
Effects of Natural Disturbances.
Wildfire. Fire kills the trees and shrubs, most of which must re-establish from seed.
Herbaceous plants lose above-ground biomass to fire, but most promptly re-sprout from
surviving below-ground organs.
·
Herb Dominated (HD)– high mortality wildfire recycles the stand in this early
successional condition while a low mortality wildfire maintains this condition
24
·
·
·
Herbs - Shrubs (HS)– high mortality wildfires send the stand back to the HD
condition while a low mortality wildfire maintains the stand in this successional
condition
Shrubs - Trees (ST)– high mortality wildfires send the stand back to the HD
condition while a low mortality wildfire maintains the stand in this successional
condition
Tree Dominated (TD) – high mortality wildfires send the stand back to the HD
condition while a low mortality wildfire maintains the stand in this successional
condition
Insects/Pathogens. Pinyon decline (combination of black stain root fungus and
engraver bark beetles) kills pinyon trees of all sizes, but does not directly affect junipers,
shrubs, or herbs.
·
·
·
·
Herb Dominated (HD) –not susceptible to black stain or beetles
Herbs - Shrubs (HS) – high or low mortality pinyon decline maintains the HS
stage because the juniper component survives the outbreak, after which the stand
resumes its usual successional trajectory
Shrubs - Trees (ST) – either high or low mortality pinyon decline returns an
affected stand to the HS stage
Tree Dominated (TD) – high mortality pinyon decline returns the stand to the HS
condition while low mortality pinyon decline returns the stand to the ST condition
Reference Conditions and 20th Century Changes.
Prior to Euro-American settlement in the late 1800s, the pinyon-juniper landscape
was composed of a mosaic of stands in different stages of succession following earlier
disturbances. We have no specific information about proportions of successional stages
or patch sizes and shapes in the reference landscape. Proportions and patch sizes
probably fluctuated over time, with more and larger patches of early successional stages
during dry periods with greater fire frequency, and a greater preponderance of late
successional stages during wet periods with reduced fire frequency. Although
proportions fluctuated with climatic fluctuation, at a broad scale probably every stage
was always represented somewhere in the landscape. See chapter 6 in Romme et al.
(2003) for a discussion of pinyon-juniper forests in the South Central Highlands Section
which includes the Uncompahgre Plateau.
RMLANDS State Transition Diagram for Pinyon-Juniper-Oak-Serviceberry
Woodland
25
26
13. Oak-Serviceberry Shrubland
Distribution.
Oak-Serviceberry Shrubland is an extensive cover type found at middle to high
elevations on both sides of the Uncompahgre Plateau, on ridges of Dakota sandstone and
especially on unstable soils in concave basins of Morrison shale. Similar communities
are found in many parts of western Colorado (Floyd et al. 2000, Spencer et al. 1996,
Johnston and Huckaby 2001).
Structure & Composition.
This cover type consists of moderately dense to dense stand of tall shrubs (up to 3 m),
including Quercus gambelii, Amelanchier utahensis, and often Symphoricarpos spp.,
with an understory of graminoids such as Poa fendleriana and Carex geyeri, plus a
variety of forbs, including Wyethia amplexicaulis, Lupinus spp., Lathyrus pauciflorus,
Lathyrus leucanthus, and Delphinium nelsoni.
Stand Conditions and Successional Trends.
·
·
·
Herbs - Shrubs (HS) – During the first decade after a severe disturbance, stands
are dominated by re-sprouting stems of the shrub species that were present at the
time of the fire, plus re-sprouting graminoids and forbs … persists from stand age
0 until age 20-30
Early Shrub Dominated (ESD) – After about a decade, the re-sprouting shrubs
consist of dense clumps <2 m tall. Herbs are present between clumps, but not
within the dense clumps … persists from stand age 20-30 until age 50-70
Late Shrub Dominated (LSD) – After several decades, the shrubs develop a
taller (2-3 m), more open canopy. Herbs grow between clumps of shrubs and also
beneath the shrub canopies … persists from stand age 50-70 until the next standreplacing disturbance
Effects of Natural Disturbances.
Wildfire. Fire kills the above-ground portions of the shrubs and herbs, but most
shrubs and herbs promptly re-sprout from surviving below-ground organs.
·
·
·
Herbs - Shrubs (HS) – high mortality wildfire recycles the stand in this early
successional condition while a low mortality wildfire maintains this condition
Early Shrub Dominated (ESD) – a high mortality wildfire returns the stand to
the HS condition while a low mortality fire maintains the stand in this condition
Late Shrub Dominated (LSD) – a high mortality wildfire returns the stand to the
HS condition while a low mortality fire maintains the stand in this condition
Reference Conditions and 20th Century Changes.
Prior to Euro-American settlement in the late 1800s, the shrub-dominated landscape
was composed of a mosaic of stands in different stages of succession following earlier
disturbances. We have no specific information about proportions of successional stages
or patch sizes and shapes in the reference landscape. A study in the shrublands of Mesa
Verde National Park, ca 100 km to the south, determined that an area equal to the entire
27
extent of the shrubland burned approximately every century during the reference period
(Floyd et al. 2000), maintaining all successional stages in the landscape. A similar fire
history may have characterized the shrublands of the Uncompahgre Plateau. However,
fire intervals, proportions of post-fire successional stages, and patch sizes probably
fluctuated over time, with more and larger patches of early successional stages during dry
periods of greater fire frequency, and a greater preponderance of late successional stages
during wet periods of reduced fire frequency. Although proportions fluctuated with
climatic fluctuation, at a broad scale probably every stage was always represented
somewhere in the landscape. Some of the stands of oak-serviceberry shrubland that we
see today may the result of repeated fires that eliminated the trees within a PinyonJuniper-Oak-Serviceberry Woodland potential vegetation type, as has been documented
in Mesa Verde (Floyd et al. 2000). See chapter 6 in Romme et al. (2003) for a discussion
of mountain shrublands in the South Central Highlands Section which includes the
Uncompahgre Plateau.
RMLANDS State Transition Diagram for Oak-Serviceberry Shrubland
28
14. Ponderosa Pine –Oak Forest
Distribution.
This cover type is found at middle elevations on Dakota sandstone, especially in the
southern portion of the Uncompahgre Plateau. It is relatively widespread in the southern
portion of the plateau but uncommon on the rest of the Uncompahgre Plateau. However,
similar communities are found in many portions of the Colorado Plateau and southern
Rocky Mountain regions (Peet 1988, Spencer et al. 1996, Johnston and Huckaby 2001,
Romme et al. 2003).
Structure & Composition.
Ponderosa pine – Oak Forest consists of sparse to dense stands of Pinus ponderosa
with occasional Pseudotsuga menziesii, Populus tremuloides, Juniperus scopulorum, or
Pinus edulis. There often is a well developed understory of Quercus gambelii and
occasional other shrubs, including Cercocarpus montanus, Amelanchier utahensis,
Amelanchier alnifolia, Ceanothus fendleri, Purshia tridentata, Mahonia repens,
Arctostaphylos uva-ursi, and Symphoricarpos rotundifolia. The ground layer vegetation
is extremely variable, depending on aspect, soil type, overstory canopy cover, grazing
and fire history. Common ground layer species include Erigeron formosissimus,
Potentilla hippiana, Solidago simplex, Penstemon barbatus, Geranium caespitosum,
Fragaria virginiana, Pulsatilla patens, Antennaria rosea, Pseudocymopterus montanus,
Lathyrus leucanthus, Achillea lanulosa, Danthonia parryi, Festuca arizonica,
Muhlenberia montana, Koelaria macrantha, Elymus elymoides, Poa fendleriana, Poa
pratensis, and Carex geyeri (species list from J. Redders, San Juan National Forest, and
personal observations).
Stand Conditions and Successional Trends.
·
·
·
·
·
Stand Initiation (SI) – grasses, forbs, low shrubs, and sparse to moderate cover
of trees (primarily Pinus ponderosa)–seedlings/saplings (open canopy) … persists
from stand age 0 until age 20-60
Stem Exclusion (SE) – sparse ground cover of grasses, forbs, and shrubs;
moderate to dense cover of trees (primarily Pinus ponderosa)–pole size (closed
canopy) … persists from stand age 20-60 until age 140-200
Understory Reinitiation (UR) – heterogeneous ground cover of grasses, forbs,
and shrubs (primarily Quercus gambelii); varying density of trees (primarily
Pinus ponderosa)–variable size classes (patchy closed canopy) … persists from
stand age 140-200 until age 300-400
Shifting Mosaic (SM) – heterogeneous ground cover of grasses, forbs, and shrubs
(primarily Quercus gambelii); variable density of trees (primarily Pinus
ponderosa)–variable size classes, but mostly closed canopy (due to the prolonged
absence of wildfire) … persists from stand age 300-400 until the next standreplacing disturbance
Fire Maintained Open canopy (FMO) – moderate to dense ground cover of
grasses, forbs, and low shrubs (primarily Quercus gambelii); low density of large
trees (trees (primarily Pinus ponderosa)–variable size classes with patchy
distribution (open canopy) … this condition develops when low mortality fire
29
burns a stand in the UR or SM condition; it persists as long as low mortality fire
continue to occur periodically
Effects of Natural Disturbances.
Wildfire. wildfires are common and frequent, mortality depends on vegetation
vulnerability and wildfire intensity. Low mortality fires kill small trees and consume
above-ground portions of shrubs and herbs, but do not kill large trees or below-ground
organs of most shrubs and herbs which promptly re-sprout. High mortality fires kill large
as well as small trees, and may kill many of the shrubs and herbs as well.
·
·
·
·
·
Stand Initiation (SI) – high mortality wildfire recycles the stand in this early
successional SI condition while a low mortality wildfire maintains the condition
Stem Exclusion (SE) – high mortality wildfires return the stand to the SI
condition while low mortality wildfire can either push the stand up to the UR
condition or maintain the SE stand condition
Understory Reinitiation (UR) – high mortality wildfires return the stand to the
SI condition while low mortality wildfires can either accelerate the transition up
to the FMO stand condition or maintain the UR condition
Shifting Mosaic (SM) – high mortality wildfires return the stand to the SI
condition while low mortality wildfires will facilitate stand transition up to the
FMO condition
Fire Maintained Open canopy (FMO) – high mortality wildfires return the stand
to the SI condition while low mortality wildfires maintain the stand in the FMO
condition
Insects/Pathogens. Mountain pine beetle kills ponderosa pine trees, especially in the
larger size classes (> ca. 8 inches dbh), but does not directly affect smaller pines; nor
does it directly affect other tree species, shrubs, or herbs
·
·
·
·
·
Stand Initiation (SI) – high mortality outbreak recycles the stand in the SI stand
condition while a low mortality outbreak maintains the condition
Stem Exclusion (SE) –a high mortality outbreak returns the stand to the SI
condition while a low mortality outbreak can either accelerate the stand up to the
UR condition or maintain the stand in this condition
Understory Reinitiation (UR) – a high mortality outbreak returns the stand to the
SI condition while a low mortality occurrence can either accelerate the transition
up to the SM stage or maintain the stand in the UR condition
Shifting Mosaic (SM) – a high mortality outbreak returns the stand to the SI
condition while a low mortality outbreak maintains the stand in the SM condition
Fire Maintained Open canopy (FMO) – a high mortality beetle outbreak returns
the stand to the SI stage while a low mortality outbreak maintains the stand in the
FMO condition
Reference Conditions and 20th Century Changes.
Most ponderosa pine forests in southwestern Colorado probably were of lower
density during the pre-1880 reference period than they are today. Open stands of large,
30
multi-aged trees were maintained in part by recurrent, low mortality fires, i.e., the “Fire
Maintained Open canopy” stand condition described above. Mean fire intervals in
ponderosa pine forests of the San Juan Mountains, ca 100 km to the south, ranged from
10 – 20 years during the reference period (Romme et al. 2003, Grissino-Mayer et al. in
press). Each of the other stages also was represented in the landscape, but probably none
of the others was as extensive as this open, fire-maintained structural condition. See
Chapter 2 in Romme (2003) for a discussion of reference conditions and 20th century
changes in ponderosa pine forests of the South Central Highlands Section which includes
the Uncompahgre Plateau.
RMLANDS State Transition Diagram for Ponderosa Pine – Oak Forest
31
15. Ponderosa Pine – Oak - Aspen Forest
Distribution.
This cover type is found at middle elevations on Dakota sandstone, especially in the
southern portion of the Uncompahgre Plateau. It is relatively widespread in the southern
portion of the plateau but uncommon elsewhere on the Uncompahgre Plateau. Ponderosa
Pine – Oak Forest and Ponderosa Pine – Oak – Aspen Forest overlap in distribution; it is
not known why some stands contain aspen while others do not. Similar communities are
found in many portions of the Colorado Plateau and southern Rocky Mountain regions
(Johnston and Huckaby 2001, Romme et al. 2003).
Structure & Composition.
Ponderosa pine – Oak Forest consists of sparse to dense stands of Pinus ponderosa
with occasional Pseudotsuga menziesii, Populus tremuloides, Juniperus scopulorum, or
Pinus edulis. There often is a well developed understory of Quercus gambelii and
occasional other shrubs, including Cercocarpus montanus, Amelanchier utahensis,
Amelanchier alnifolia, Ceanothus fendleri, Purshia tridentata, Mahonia repens,
Arctostaphylos uva-ursi, and Symphoricarpos rotundifolia. The ground layer vegetation
is extremely variable, depending on aspect, soil type, overstory canopy cover, grazing
and fire history. Common ground layer species include Erigeron formosissimus,
Potentilla hippiana, Solidago simplex, Penstemon barbatus, Geranium caespitosum,
Fragaria virginiana, Pulsatilla patens, Antennaria rosea, Pseudocymopterus montanus,
Lathyrus leucanthus, Achillea lanulosa, Danthonia parryi, Festuca arizonica,
Muhlenberia montana, Koelaria macrantha, Elymus elymoides, Poa fendleriana, Poa
pratensis, and Carex geyeri (species list from J. Redders, San Juan National Forest, and
personal observations). Structure and composition are very similar to the ponderosa pine
– oak forest, described above, except that Potr is also an important component of this
vegetation type. Young stands or frequently burned stands may be dominated by Potr,
but Potr is gradually replaced by conifers over the course of succession in the absence of
disturbance.
Stand Conditions and Successional Trends.
·
·
·
Stand Initiation (SI) – grasses, forbs, low shrubs, and sparse to moderate cover
of trees (Populus tremuloides are much more abundant than Pinus ponderosa)
that are seedlings/saplings (open canopy), classified as Aspen for purposes of
FRAGSTATS analysis and wildlife habitat models … persists from stand age 0
until age 20-40
Stem Exclusion (SE) – moderate ground cover of grasses, forbs, and shrubs;
moderate to dense cover of trees (primarily Populus tremuloides with Pinus
ponderosa secondary) that are pole size (closed canopy), classified as Aspen for
purposes of FRAGSTATS analysis and wildlife habitat models … persists from
stand age 20-40 until age 80-120
Understory Reinitiation (UR) – heterogeneous ground cover of grasses, forbs,
and shrubs; varying density of trees (primarily Pinus ponderosa, with declining
Populus tremuloides) that are variable size classes (patchy closed canopy) …
persists from stand age 80-120 until age 300-400
32
·
·
Shifting Mosaic (SM) – heterogeneous ground cover of grasses, forbs, and
shrubs; variable density of trees (Pinus ponderosa are dominant species with
scattered remnant Populus tremuloides) that are variable size classes, but mostly
closed canopy (due to the prolonged absence of wildfire) … persists from stand
age 300-400 until the next stand-replacing disturbance
Fire Maintained Open canopy (FMO) – moderate to dense ground cover of
grasses, forbs, and low shrubs; low density of large trees (Pinus ponderosa are
still much more abundant than the scattered dense patches of regenerating
Populus tremuloides) that are variable size classes, patchy distribution (open
canopy) … this condition develops when low mortality fire burns a stand in the
UR or SM condition; it persists as long as low mortality fire continue to occur
periodically
Effects of Natural Disturbances.
Wildfire. Wildfires were frequent during the reference period; mortality depends on
vegetation vulnerability and wildfire intensity. Low mortality fires kill small trees and
consume above-ground portions of shrubs and herbs, but do not kill large trees or belowground organs of most shrubs and herbs which promptly re-sprout. High mortality fires
kill large as well as small trees, and may kill many of the shrubs and herbs as well.
Aspen stems are very vulnerable to fire damage, but the root system usually survives
even severe fires and promptly re-sprouts.
·
·
·
·
·
Stand Initiation (SI) – high mortality wildfire recycles the stand in the SI
condition while a low mortality wildfire maintains the condition
Stem Exclusion (SE) – high mortality wildfires return the stand to the SI
condition while low mortality wildfires can either push the stand to the UR
condition or maintain the SE stand condition
Understory Reinitiation (UR) – high mortality wildfires return the stand to the
SI condition while low mortality wildfires can either accelerate the transition up
to the FMO stand condition or maintain the UR condition
Shifting Mosaic (SM) – high mortality wildfires return the stand to the SI
condition while low mortality wildfires cause stand transition up to the FMO
condition
Fire Maintained Open canopy (FMO) – high mortality wildfires return the stand
to the SI condition while low mortality wildfires maintain the stand in the FMO
condition
Insects/Pathogens. Mountain pine beetle kills ponderosa pine trees, especially in the
larger size classes (> ca. 8 inches dbh), but does not directly affect smaller pines; nor
does it directly affect other tree species, shrubs, or herbs
·
·
Stand Initiation (SI) – high or low mortality outbreaks maintain the stand in the
SI stand condition
Stem Exclusion (SE) –a high or low mortality outbreak can either accelerate the
stand up to the UR condition or maintain the stand in the SE condition
33
·
·
·
Understory Reinitiation (UR) – a high or low mortality occurrence can either
accelerate the transition up to the SM stage or maintain the stand in the UR
condition
Shifting Mosaic (SM) – a high mortality outbreak returns the stand to the SI
condition while a low mortality outbreak maintains the stand in the SM condition
Fire Maintained Open canopy (FMO) – a high mortality beetle outbreak returns
the stand to the SI stage while a low mortality outbreak maintains the stand in the
FMO condition
Reference Conditions and 20th Century Changes.
Most ponderosa pine forests in southwestern Colorado probably were of lower
density during the pre-1880 reference period than they are today. Open stands of large,
multi-aged trees were maintained in part by recurrent, low mortality fires, i.e., the “Fire
Maintained Open canopy” stand condition described above. Mean fire intervals in
ponderosa pine forests of the San Juan Mountains, ca 100 km to the south, ranged from
10 – 20 years during the reference period (Romme et al. 2003, Grissino-Mayer et al. in
press). Each of the other stages also was represented in the landscape, but probably none
of the others was as extensive as this open, fire-maintained structural condition. See
Chapter 2 in Romme (2003) for a discussion of reference conditions and 20th century
changes in ponderosa pine forests of the South Central Highlands Section which includes
the Uncompahgre Plateau.
RMLANDS State Transition Diagram for Ponderosa Pine – Oak- Aspen Forest
34
16. Warm Dry Mixed-Conifer Forest
Distribution.
This cover type is found at middle elevations, especially in the southwestern portion
of the Uncompahgre Plateau. Similar communities are found in many portions of the
Colorado Plateau and southern Rocky Mountain regions (Jamieson et al. 1996, Johnston
and Huckaby 2001, Romme et al. 2003).
Structure & Composition.
Warm Dry Mixed-Conifer Forest consists of sparse to moderately dense stands of
Pinus ponderosa mixed with Pseudotsuga menziesii, but Populus tremuloides is absent.
The understory usually is dominated by Quercus gambelii, with other shrubs often
present also, including Ceanothus fendleri, Amelanchier alnifolia, Symphoricarpos
rotundifolius, Mahonia repens, Chimaphila umbellatum, Arctostaphylos uva-ursi,
Arctostaphylos patula. Common grasses and forbs include Koeleria macranthra,
Elymus elymoides, Poa fendleriana, Poa pratensis, Carex geyeri, Delphium nelsoni,
Mertensia fusiformis, Erigeron formosissimus, Potentilla hippiana, Solidago simplex,
Geranium caespitosum, Antennaria rosea, Pseudocymopterus montanus, Lathyrus
leucanthus, and Achillea lanulosa, (species list from J. Redders, San Juan National
Forest, and personal observations).
Stand Conditions and Successional Trends.
·
·
·
·
·
Stand Initiation (SI) – grasses, forbs, low shrubs, and sparse to moderate cover
of trees–seedlings/saplings (open canopy) … persists from stand age 0 until age
20-60
Stem Exclusion (SE) – sparse ground cover of grasses, forbs, and shrubs;
moderate to dense cover of trees–pole size (closed canopy) … persists from stand
age 20-60 until age 140-200
Understory Reinitiation (UR) – heterogeneous ground cover of grasses, forbs,
and shrubs; varying density of trees–variable size classes (patchy closed canopy)
… persists from stand age 140-200 until age 300-400
Shifting Mosaic (SM) – heterogeneous ground cover of grasses, forbs, and
shrubs; variable density of trees (Pinus ponderosa declining or absent; no
reproduction; but Pseudotsuga menziesii increasing in density in all size classes)–
variable size classes, but mostly closed canopy (due to the prolonged absence of
wildfire) … persists from stand age 300-400 until the next stand-replacing
disturbance
Fire Maintained Open canopy (FMO) – moderate to dense ground cover of
grasses, forbs, and low shrubs; low density of large trees (Pinus ponderosa
reproduction present)–variable size classes, patchy distribution (open canopy) …
this condition develops when low mortality fire burns a stand in the UR or SM
condition; it persists as long as low mortality fire continue to occur periodically
Effects of Natural Disturbances.
Wildfire. Low mortality fires kill small trees and consume above-ground portions of
shrubs and herbs, but do not kill large trees or below-ground organs of most shrubs and
35
herbs which promptly re-sprout. High mortality fires kill large as well as small trees, and
may kill many of the shrubs and herbs as well.
·
·
·
·
·
Stand Initiation (SI) – a high mortality wildfire recycles the stand through the SI
condition while a low mortality wildfire maintains the stand in this condition
Stem Exclusion (SE) – high mortality wildfires return the stand to the SI
condition while low mortality wildfires can either accelerate transition to the UR
condition or maintain the stand in the SE condition
Understory Reinitiation (UR) – high mortality wildfires return the stand to the
SI condition while low mortality wildfires can either accelerate transition to the
FMO condition or maintain the stand in the UR condition
Shifting Mosaic (SM) – high mortality wildfires return the stand to the SI
condition while low mortality wildfires will cause stand transition up to the FMO
condition
Fire-Maintained Open canopy (FMO) – high mortality wildfires return the stand
to the SI stand condition while low mortality wildfires maintain the stand in the
FMO stand condition
Insects/Pathogens. Mountain pine beetle and Douglas-fir beetle kill ponderosa pine
and Douglas-fir trees, respectively, especially in the larger size classes (> ca. 8 inches
dbh). Western spruce budworm gradually defoliates Douglas-fir trees and saplings of all
sizes by killing terminal branch buds. Affected trees may die after many years of
repeated defoliation, or become susceptible to bark beetle attack. None of these insects
directly affect smaller individuals of ponderosa pine and Douglas-fir, or other tree
species, shrubs, or herbs.
·
·
·
·
·
Stand Initiation (SI) – a high mortality outbreak of all four insects recycles the
stand through the SI condition while any other combination of insect outbreak
maintains the SI condition
Stem Exclusion (SE) – a high mortality outbreak of all four insects returns the
stand to the SI condition while any other combination of insect outbreak can
either accelerate succession to the UR condition or maintain the stand in the SE
condition
Understory Reinitiation (UR) – a high mortality outbreak of all four insects
returns the stand to the SI condition while any other combination of insect
outbreak can either accelerate the stand up to the SM condition or maintain the
stand in the UR condition
Shifting Mosaic (SM) – a high mortality outbreak of all four insects returns the
stand to the SI condition while any other combination of insect outbreak
maintains the stand in the SM condition
Fire Maintained Open canopy (FMO) – a high mortality outbreak of all four
insects returns the stand to the SI condition while any other combination of insect
outbreak maintains the stand in the FMO condition
Reference Conditions and 20th Century Changes.
36
Warm dry mixed conifer forests resembled ponderosa pine – oak forests in that many
stands were maintained at low density by recurrent fire. However, the other structural
stages also were present in variable amounts across the landscape. The extent of the firemaintained open canopy stage probably has decreased substantially since Euro-American
settlement, primarily because of fire exclusion. See chapters 2 and 3 in Romme et al.
(2003) for a discussion of the composition, structure, and dynamics of ponderosa pine
and mixed conifer forests of the South Central Highlands Section which includes the
Uncompahgre Plateau.
RMLANDS State Transition Diagram for Warm Dry Mixed-Conifer Forest
37
17. Warm Dry Mixed-Conifer with Aspen Forest
Distribution.
This cover type is found at middle elevations, primarily in the southwestern portion of
the Uncompahgre Plateau. Its distribution overlaps the distribution of Warm-Dry Mixed
Conifer Forest; the reason why some mixed conifer stands also contain aspen and others
do not is unknown. Similar communities are found in many portions of the Colorado
Plateau and southern Rocky Mountain regions (Johnston and Huckaby 2001, Romme et
al. 2003).
Structure & Composition.
Warm Dry Mixed-Conifer with Aspen Forest consists of sparse to moderately dense
stands of Pinus ponderosa mixed with Pseudotsuga menziesii and Populus tremuloides.
The understory usually is dominated by Quercus gambelii, with other shrubs often
present also, including Ceanothus fendleri, Amelanchier alnifolia, Symphoricarpos
rotundifolius, Mahonia repens, Chimaphila umbellatum, Arctostaphylos uva-ursi,
Arctostaphylos patula. Common grasses and forbs include Koeleria macranthra,
Elymus elymoides, Poa fendleriana, Poa pratensis, Carex geyeri, Delphium nelsoni,
Mertensia fusiformis, Erigeron formosissimus, Potentilla hippiana, Solidago simplex,
Geranium caespitosum, Antennaria rosea, Pseudocymopterus montanus, Lathyrus
leucanthus, and Achillea lanulosa, (species list from J. Redders, San Juan National
Forest, and personal observations).
Species composition of this vegetation is very similar to that of the warm-dry mixed
conifer forest, described above, except that Populus tremuloides is also an important
component of this type. Young stands or frequently burned stands may be dominated by
Populus tremuloides, but Populus tremuloides is gradually replaced by conifers over the
course of succession in the absence of disturbance.
Stand Conditions and Successional Trends.
·
·
·
·
Stand Initiation (SI) – grasses, forbs, low shrubs, and sparse to moderate cover
of trees–seedlings/saplings with aspen much more abundant than conifers (open
canopy), classify as Aspen for purposes of FRAGSTATS analysis and wildlife
habitat models … persists from stand age 0 until age 20-40
Stem Exclusion (SE) – sparse ground cover of grasses, forbs, and shrubs;
moderate to dense cover of trees–pole size with aspen more abundant than
conifers (closed canopy), classify as Aspen for purposes of FRAGSTATS
analysis and wildlife habitat models … persists from stand age 20-40 until age 80120
Understory Reinitiation (UR) – heterogeneous ground cover of grasses, forbs,
and shrubs; varying density of trees (conifers more abundant than the declining
Populus tremuloides) – variable size classes (patchy closed canopy) … persists
from stand age 80-120 until age 300-400
Shifting Mosaic (SM) – heterogeneous ground cover of grasses, forbs, and
shrubs; variable density of trees (Pinus ponderosa declining or absent; no
reproduction; conifers much more abundant than the remnant Populus
tremuloides) – variable size classes, but mostly closed canopy (due to the
38
·
prolonged absence of wildfire) … persists from stand age 300-400 until the next
stand-replacing disturbance
Fire Maintained Open canopy (FMO) – moderate to dense ground cover of
grasses, forbs, and low shrubs; low density of large trees (Pinus ponderosa
reproduction present; Pseudotsuga menziesii and Pinus ponderosa more abundant
than the scattered dense patches of Populus tremuloides) – variable size classes,
patchy distribution (open canopy) … this condition develops when low mortality
fire burns a stand in the UR or SM condition; it persists as long as low mortality
fire continue to occur periodically
Effects of Natural Disturbances.
Wildfire. Low mortality fires kill small trees and consume above-ground portions of
shrubs and herbs, but do not kill large trees or below-ground organs of most shrubs and
herbs which promptly re-sprout. High mortality fires kill large as well as small trees, and
may kill many of the shrubs and herbs as well.
·
·
·
·
·
Stand Initiation (SI) – high mortality wildfire recycles the stand through the SI
condition while a low mortality wildfire maintains this condition
Stem Exclusion (SE) – high mortality wildfires return the stand to the SI
condition while a low mortality wildfire can either accelerate transition up to the
UR condition or maintain the stand in the SE condition
Understory Reinitiation (UR) – high mortality wildfires return the stand to the
SI condition while a low mortality wildfire can either accelerate transition up to
the FMO condition or maintain the stand in the UR condition
Shifting Mosaic (SM) – high mortality wildfires return the stand to the SI
condition while a low mortality wildfire will cause transition up to the FMO
condition
Fire-Maintained Open canopy (FMO) – high mortality wildfires return the stand
to the SI stand condition while a low mortality wildfire maintain the stand in the
FMO condition
Insects/Pathogens. Mountain pine beetle and Douglas-fir beetle kill ponderosa pine
and Douglas-fir trees, respectively, especially in the larger size classes (> ca. 8 inches
dbh). Western spruce budworm gradually defoliates Douglas-fir trees and saplings of all
sizes by killing terminal branch buds. Affected trees may die after many years of
repeated defoliation, or become susceptible to bark beetle attack. None of these insects
directly affect smaller individuals of ponderosa pine and Douglas-fir, or other tree
species, shrubs, or herbs.
·
·
·
Stand Initiation (SI) – high or low mortality outbreaks maintain the stand in the
SI stand condition
Stem Exclusion (SE) – a high or low mortality outbreak can either accelerate the
stand up to the UR condition or maintain the stand in the SE condition
Understory Reinitiation (UR) – a high or low mortality occurrence can either
accelerate the transition up to the SM stage or maintain the stand in the UR
condition
39
·
·
Shifting Mosaic (SM) – a high mortality outbreak of all four insects returns the
stand to the SI condition while any other combination of insect outbreak
maintains the stand in the SM condition
Fire Maintained Open canopy (FMO) – a high mortality beetle outbreak of all
four insects returns the stand to the SI stage while any other combination of
outbreak maintains the stand in the FMO condition
Reference Conditions and 20th Century Changes.
Warm dry mixed conifer forests resembled ponderosa pine – oak forests in that many
stands were maintained at low density by recurrent fire. However, the other structural
stages also were present in variable amounts across the landscape. Some stands,
especially those in early successional stages following severe disturbances or those
having recurrent low mortality fire, were dominated by aspen, but other stands contained
little or no aspen. The extent of the fire-maintained open canopy stage probably has
decreased substantially since Euro-American settlement, primarily because of fire
exclusion. See chapters 2, 3, and 4 in Romme et al. (2003) for a discussion of the
composition, structure, and dynamics of ponderosa pine, mixed conifer, and aspen forests
of the South Central Highlands Section which includes the Uncompahgre Plateau.
RMLANDS State Transition Diagram for Warm Dry Mixed-Conifer with Aspen Forest
40
18. Cool Moist Mixed-Conifer Forest
Distribution.
This cover type is found on north-facing slopes at middle and on all aspects at high
elevations, especially in the central portion of the Uncompahgre Plateau. Similar
communities are elsewhere in the southern Rocky Mountain region (Peet 1988, Jamieson
et al. 1996, Johnston and Huckaby 2001, Romme et al. 2003).
Structure & Composition.
Cool Moist Mixed-Conifer Forest consists of moderate to dense stands of a mixture
of coniferous species, including Pseudotsuga menziesii, Picea engelmannii, and Abies
lasiocarpa, but Populus tremuloides is absent. A rich shrub understory is often present,
including Amelanchier alnifolia, Sambucus racemosa, Lonicera involucrata, and
Symphoricarpos spp. Common graminoids and forbs include Carex geyeri, Erigeron
eximius, Ligusticum porteri, Mertensia ciliata, Aquilegia elegantula, Orthilia secunda,
Artemisia franserioides, Viola Canadensis, Goodyera oblongifolia, Fragaria vesca,
Oreochrysum parryi, Lathyrus leucanthus, Pyrola minor, Actaea rubra, Maianthemum
stellatum, Luzula parviflora, Bromopsis Canadensis, Carex geyeri, Rubus parviflorus,
and Osmorhiza depauperata (species list from J. Redders, San Juan National Forest, and
personal observations).
Stand Conditions and Successional Trends.
·
·
·
·
Stand Initiation (SI) – grasses, forbs, low shrubs, and sparse to moderate cover
of trees–seedlings/saplings (open canopy) … persists from stand age 0 until age
30-100
Stem Exclusion (SE) – sparse ground cover of grasses, forbs, and shrubs;
moderate to dense cover of trees–pole size (closed canopy) … persists from stand
age 30-100 until age 150-250
Understory Reinitiation (UR) – heterogeneous ground cover of grasses, forbs,
and shrubs; varying density of trees–variable size classes (patchy closed canopy)
… persists from stand age 150-250 until age 300-450
Shifting Mosaic (SM) – heterogeneous ground cover of grasses, forbs, and
shrubs; variable density of trees –variable size classes (patchy closed canopy) …
persists from stand age 300-450 until the next stand-replacing disturbance
Effects of Natural Disturbances.
Wildfire. Fires tend to be high mortality, stand-replacing fires that initiate a process
of post-fire forest succession. High mortality fires kill large as well as small trees, and
may kill many of the shrubs and herbs as well, although below-ground organs of at least
some individual shrubs and herbs survive and re-sprout. Low mortality fires may
consume surface fuels (i.e., surface fire) and may result in the death of some overstory
trees, but the majority survive (i.e., mosaic fire).
·
Stand Initiation (SI) – a high mortality wildfire recycles the stand through the SI
condition while a low mortality wildfire maintains the condition
41
·
·
·
Stem Exclusion (SE) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire can either move the stand up to the UR
condition or maintain the stand in the SE condition
Understory Reinitiation (UR) – a high mortality wildfire returns the stand to the
SI condition while a low mortality wildfire can either move the stand up to the
SM condition or maintain the stand in the UR condition
Shifting Mosaic (SM) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire maintains the SM condition
Insects/Pathogens. Spruce beetle and Douglas-fir beetle kill Engelmann spruce and
Douglas-fir trees, respectively, especially in the larger size classes (> ca. 8 inches dbh).
Western spruce budworm gradually defoliates Douglas-fir and subalpine fir trees and
saplings of all sizes by killing terminal branch buds. Affected trees may die after many
years of repeated defoliation, or become susceptible to bark beetle attack. None of these
insects directly affect smaller individuals of spruce and Douglas-fir, or other tree species,
shrubs, or herbs.
·
·
·
·
Stand Initiation (SI) – a high mortality outbreak of all three insects recycles the
stand through the SI condition while any other combination maintains the
condition
Stem Exclusion (SE) – a high mortality outbreak of all three insects sends the
stand back to the SI condition while any other combination can either accelerate
the stand up to the UR condition or maintain the stand in the SE condition
Understory Reinitiation (UR) – a high mortality outbreak of all three insects
sends the stand back to the SI condition while any other combination can either
accelerate the stand up to the SM condition or maintain the stand in the UR
condition
Shifting Mosaic (SM) –a high mortality outbreak of all three insects returns the
stand to the SI condition while any other combination of outbreak will maintain
the SM condition
Reference Conditions and 20th Century Changes.
Prior to Euro-American settlement in the late 1800s, the mixed conifer landscape
consisted of a mosaic of successional stages developing after previous disturbances.
Some young stands were dominated by aspen, as described below for the cool moist
mixed conifer forest with aspen, but other stands contained no aspen. We have no
specific information about relative proportions of stages or about patch sizes and shapes.
Proportions and patch sizes probably fluctuated through time in response to climatic
variability and variable fire frequency. See chapter 3 in Romme et al. (2003) for a
discussion of mixed conifer forests in the South Central Highlands Section which
includes the Uncompahgre Plateau.
RMLANDS State Transition Diagram for Cool Moist Mixed-Conifer Forest
42
43
19. Cool Moist Mixed-Conifer with Aspen Forest
Distribution.
This cover type is found on north-facing slopes at middle and on all aspects at high
elevations, especially in the central portion of the Uncompahgre Plateau. Its distribution
overlaps that of the Cool Moist Mixed-Conifer Forest; the reason why some stands have
aspen and others do not is unknown. Similar communities are elsewhere in the southern
Rocky Mountain region (Peet 1988, Jamieson et al. 1996, Johnston and Huckaby 2001,
Romme et al. 2003).
Structure & Composition.
Cool Moist Mixed-Conifer with Aspen Forest consists of moderate to dense stands of
a mixture of coniferous species, including Pseudotsuga menziesii, Picea engelmannii,
and Abies lasiocarpa, as well as Populus tremuloides. A rich shrub understory is often
present, including Amelanchier alnifolia, Sambucus racemosa, Lonicera involucrata, and
Symphoricarpos spp. Common graminoids and forbs include Carex geyeri, Erigeron
eximius, Ligusticum porteri, Mertensia ciliata, Aquilegia elegantula, Orthilia secunda,
Artemisia franserioides, Viola Canadensis, Goodyera oblongifolia, Fragaria vesca,
Oreochrysum parryi, Lathyrus leucanthus, Pyrola minor, Actaea rubra, Maianthemum
stellatum, Luzula parviflora, Bromopsis Canadensis, Carex geyeri, Rubus parviflorus,
and Osmorhiza depauperata (species list from J. Redders, San Juan National Forest, and
personal observations). Composition and structure are similar to Cool Moist MixedConifer Forest, except that aspen also is an important component of this cover type.
Stand Conditions and Successional Trends.
·
·
·
·
Stand Initiation (SI) – grasses, forbs, low shrubs, and sparse to moderate cover
of trees–seedlings/saplings (open canopy), classify as Aspen for purposes of
FRAGSTATS analysis and wildlife habitat models … persists from stand age 0
until age 20-40
Stem Exclusion (SE) – sparse ground cover of grasses, forbs, and shrubs;
moderate to dense cover of trees–pole size (closed canopy), classify as Aspen for
purposes of FRAGSTATS analysis and wildlife habitat models … persists from
stand age 20-40 until age 80-120
Understory Reinitiation (UR) – heterogeneous ground cover of grasses, forbs,
and shrubs; varying density of trees–variable size classes (patchy closed canopy)
… persists from stand age 80-120 until age 300-450
Shifting Mosaic (SM) – heterogeneous ground cover of grasses, forbs, and
shrubs; variable density of trees –variable size classes (patchy closed canopy) …
persists from stand age 300-450 until the next stand-replacing disturbance
Effects of Natural Disturbances.
Wildfire. Fires tend to be high mortality, stand-replacing fires that initiate a process
of post-fire forest succession. High mortality fires kill large as well as small trees, and
may kill many of the shrubs and herbs as well, although below-ground organs of at least
some individual shrubs and herbs survive and re-sprout. Aspen stems are very vulnerable
44
to fire damage, but the root system usually survives even severe fires and promptly resprouts. Low mortality fires may consume surface fuels (i.e., surface fire) and may result
in the death of some overstory trees, but the majority survive (i.e., mosaic fire).
·
·
·
·
Stand Initiation (SI) – a high mortality wildfire recycles the stand through the SI
condition while a low mortality wildfire maintains the condition
Stem Exclusion (SE) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire can either move the stand up to the UR
condition or maintain the stand in the SE condition
Understory Reinitiation (UR) – a high mortality wildfire returns the stand to the
SI condition while a low mortality wildfire can either move the stand up to the
SM condition or maintain the stand in the UR condition
Shifting Mosaic (SM) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire maintains the SM condition
Insects/Pathogens. Spruce beetle and Douglas-fir beetle kill Engelmann spruce and
Douglas-fir trees, respectively, especially in the larger size classes (> ca. 8 inches dbh).
Western spruce budworm gradually defoliates Douglas-fir and subalpine fir trees and
saplings of all sizes by killing terminal branch buds. Affected trees may die after many
years of repeated defoliation, or become susceptible to bark beetle attack. None of these
insects directly affect smaller individuals of spruce and Douglas-fir, or other tree species,
shrubs, or herbs.
·
·
·
·
Stand Initiation (SI) – a high or low mortality outbreak of any of the three
insects recycles the stand through the SI condition
Stem Exclusion (SE) – a high or low mortality outbreak of any of the three
insects can either accelerate the stand up to the UR condition or maintain the
stand in the SE condition
Understory Reinitiation (UR) – a high or low mortality outbreak of any of the
three insects can either accelerate the stand up to the SM condition or maintain the
stand in the UR condition
Shifting Mosaic (SM) –a high mortality outbreak of any of the three insects
returns the stand to the SI condition while any other combination of insect
outbreak will maintain the SM condition
Reference Conditions and 20th Century Changes.
Prior to Euro-American settlement in the late 1800s, the mixed conifer landscape
consisted of a mosaic of successional stages developing after previous disturbances.
Some young stands were dominated by aspen, but other stands contained no aspen, as
described above for the cool moist mixed conifer forest. We have no specific
information about relative proportions of stages or about patch sizes and shapes.
Proportions and patch sizes probably fluctuated through time in response to climatic
variability and variable fire frequency. See chapters 3 and 4 in Romme et al. (2003) for a
discussion of mixed conifer and aspen forests in the South Central Highlands Section
which includes the Uncompahgre Plateau.
45
RMLANDS State Transition Diagram for Cool Moist Mixed-Conifer with Aspen
Forest
46
20. Pure Aspen Forest
Distribution.
Pure Aspen Forest is a widespread cover type middle to high elevations across the
Uncompahgre Plateau. Similar communities are elsewhere in the southern Rocky
Mountain region (Peet 1988, Jamieson et al. 1996, Johnston and Huckaby 2001, Romme
et al. 2003).
Structure & Composition.
Pure Aspen Forest consists of sparse to dense stands of Populus tremuloides
with no or almost no coniferous species present. Symphoricarpos oreophilus forms a
conspicuous shrub understory in many stands, sometimes with other shrub species
including Quercus gambelii, Sambucus racemosa, and Juniperus communis. Forbs
dominate the herbaceous stratum in most stands, but grasses and forbs are equally
abundant in some stands. Some common understory herbaceous species include
Thalictrum fendleri, Senecio serra, Ligusticum porteri, Geranium richardsonii,
Delphinum barbeyi, Osmorrhiza obtusa, Vicia americana, Lathyrus leucanthus,
Carex geyeri, Fragaria ovalis, Viola nuttallii, and Bromus ciliatus. Pteridium
aquilinum is also very common in some stands (species list from J. Redders, San Juan
National Forest, and personal observations).
Stand Conditions and Successional Trends.
·
·
·
·
Stand Initiation (SI) – grasses, forbs, low shrubs, and moderate to dense cover of
trees–seedlings/saplings (open canopy) … persists from stand age 0 until age 1020
Stem Exclusion (SE) – ground cover of grasses, forbs, and shrubs; moderate to
dense cover of trees–pole size (closed canopy) … persists from stand age 10-20
until age 60-100
Understory Reinitiation (UR) – heterogeneous ground cover of grasses, forbs,
and shrubs; varying density of trees–variable size classes, the older trees are from
the original cohort with a patchy closed canopy but there is an understory of
uneven aged trees… persists from stand age 60-100 until age 100-200
Shifting Mosaic (SM) – heterogeneous ground cover of grasses, forbs, and
shrubs; variable density of trees –variable size classes (patchy closed canopy) …
persists from stand age 100-200 until the next stand-replacing disturbance
Effects of Natural Disturbances.
Wildfire. Fires tend to be high mortality, stand-replacing fires that initiate a process
of post-fire forest succession. High mortality fires kill large as well as small trees, and
may kill many of the shrubs and herbs as well, although below-ground organs of at least
some individual shrubs and herbs survive and re-sprout. Aspen stems are very vulnerable
to fire damage, even in low-intensity fires, but the root system usually survives even
high-intensity fires and promptly re-sprouts. Below-ground organs of most shrubs and
herbs also tend to survive fire and to re-sprout soon afterwards. Low mortality fires may
47
consume surface fuels (i.e., surface fire) and may result in the death of some overstory
trees, but the majority survive (i.e., mosaic fire).
·
·
·
·
Stand Initiation (SI) – a high mortality wildfire recycles the stand through the SI
condition while a low mortality wildfire maintains the condition
Stem Exclusion (SE) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire can either move the stand up to the UR
condition or maintain the stand in the SE condition
Understory Reinitiation (UR) – a high mortality wildfire returns the stand to the
SI condition while a low mortality wildfire can either move the stand up to the
UR condition or maintain the stand in the UR condition
Shifting Mosaic (SM) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire maintains the SM condition
Reference Conditions and 20th Century Changes.
Prior to Euro-American settlement in the late 1800s, the aspen landscape
consisted of a mosaic of successional stages developing after previous disturbances. We
have no specific information about relative proportions of stages or about patch sizes and
shapes on the Uncompahgre Plateau. A study conducted on the western flanks of the La
Plata Mountains, ca. 100 km to the south, determined that the median stand age in the
1880s (at the end of the reference period) was about 70 years (Romme et al. 2001). This
means that about half of the stands in the landscape were > 70 years old (mature and oldgrowth successional stages) and half were < 70 years old (early successional stages). A
similar patch mosaic may have characterized the Uncompahgre Plateau during the
reference period. However, it is important to note that proportions and patch sizes
probably fluctuated through time in response to climatic variability and variable fire
frequency throughout southwestern Colorado.
Some young aspen stands contained an understory of conifers, and the aspen
component gradually declined over the course of succession. Other aspen stands
remained pure aspen, even in the mature and old-growth stages, and even though the
local habitat was climatically suitable for conifers. The persistence of aspen in these
kinds of stands may be due to recurrent, short-interval fires that eliminated the conifer
seed source and enhanced dominance by sprouting aspen (Romme et al. 2001). See
chapter 4 in Romme et al. (2003) for a discussion of aspen forests in the South Central
Highlands Section which includes the Uncompahgre Plateau.
RMLANDS State Transition Diagram for Pure Aspen Forest
48
49
21. Spruce-Fir Forest
Distribution.
This cover type is found on all aspects at the highest elevations on the Uncompahgre
Plateau. Similar communities are elsewhere in the southern Rocky Mountain region
(Peet 1988, Jamieson et al. 1996, Johnston and Huckaby 2001, Romme et al. 2003).
Structure & Composition.
Spruce-Fir Forest consists of sparse to dense stands of Picea engelmannii, and Abies
lasiocarpa, but without aspen. A well-developed layer of shrubs, including Vaccinium
myrtillus, Rubacer parviflorum, Ribes montigenum, Sambucus microbotys, and Lonicera
involucrate is often present. A rich mixture of mesophytic herbs also is often present,
including Erigeron eximius, Geranium richardsonii, Ligusticum porteri, Mertensia
ciliata, Arnica cordifolia, Aquilegia elegantula, Pedicularis racemosa, Orthilia secunda,
Artemisia franserioides, Viola canadensis, Goodyera oblongifolia, Fragaria vesca,
Oreochrysum parryi, Lathyrus leucanthus, Pyrola minor, Maianthemum stellatum,
Luzula parviflora, Anticlea elegans, Bromopsis Canadensis, Carex geyeri, and
Osmorhiza depauperata (species list from J. Redders, San Juan National Forest, and
personal observations.
Stand Conditions and Successional Trends.
·
·
·
·
Stand Initiation (SI) – grasses, forbs, low shrubs, and moderate to dense cover of
trees–seedlings/saplings (open canopy) … persists from 0 until age 30-200
Stem Exclusion (SE) – ground cover of grasses, forbs, and shrubs; moderate to
dense cover of trees–pole size (closed canopy) … persists from stand age 30-200
until age 150-300
Understory Reinitiation (UR) – heterogeneous ground cover of grasses, forbs,
and shrubs, varying density of trees–variable size classes, the older trees are from
the original cohort with a patchy closed canopy but there is an understory of
uneven aged trees … persists from stand age 150-300 until age 300-450
Shifting Mosaic (SM) – heterogeneous ground cover of grasses, forbs, and
shrubs; variable density of trees –variable size classes (patchy closed canopy) …
persists from stand age 300-450 until the next stand-replacing disturbance
Effects of Natural Disturbances.
Wildfire. Fires tend to be high mortality, stand-replacing fires that initiate a process
of post-fire forest succession. High mortality fires kill large as well as small trees, and
may kill many of the shrubs and herbs as well, although below-ground organs of at least
some individual shrubs and herbs survive and re-sprout. Low mortality fires may
consume surface fuels (i.e., surface fire) and may result in the death of some overstory
trees, but the majority survive (i.e., mosaic fire).
·
Stand Initiation (SI) – a high mortality wildfire recycles the stand through the SI
condition while a low mortality wildfire maintains the condition
50
·
·
·
Stem Exclusion (SE) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire can either accelerate the stand up to the
UR condition or maintain the stand in the SE condition
Understory Reinitiation (UR) – a high mortality wildfire returns the stand to the
SI condition while a low mortality wildfire can either accelerate the stand up to
the SM condition or maintain the stand in the UR condition
Shifting Mosaic (SM) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire maintains the stand in the SM condition
Insects/Pathogens. Spruce beetle kills Engelmann spruce trees, especially in the
larger size classes (> ca. 8 inches dbh). Western spruce budworm gradually defoliates
subalpine fire trees and saplings of all sizes by killing terminal branch buds. Affected
trees may die after many years of repeated defoliation, or become susceptible to bark
beetle attack. None of these insects directly affect smaller individuals of spruce, nor do
they affect other tree species, shrubs, or herbs.
·
·
·
·
Stand Initiation (SI) – a high mortality outbreak of both insects recycles the
stand through the SI condition while any other combination of insect outbreak
maintains the condition
Stem Exclusion (SE) – a high mortality outbreak of both insects returns the stand
to the SI condition while any other combination of insect outbreak can either
accelerate the transition up to the UR condition or maintain the stand in the SE
condition
Understory Reinitiation (UR) – a high mortality outbreak of both insects returns
the stand to the SI condition while any other combination of insect outbreaks can
either accelerate the transition up to the SM condition or maintain the stand in the
UR condition
Shifting Mosaic (SM) – a high mortality outbreak of both insects returns the
stand to the SI condition while any other combination of insect outbreaks
maintain the SM condition
Reference Conditions and 20th Century Changes.
Prior to Euro-American settlement in the late 1800s, the spruce-fir landscape
consisted of a mosaic of successional stages developing after previous disturbances.
Some early successional stages were dominated by aspen, as described below for the
spruce-fir-aspen forest cover type, and other stands were almost exclusively spruce and
fir with little or no aspen. We have no specific information about relative proportions of
successional stages or about patch sizes and shapes on the Uncompahgre Plateau. A
study in the San Juan Moutains, ca. 100 km to the south, determined that about one-tenth
of the landscape may have been covered by young stands (< 50 years old), and a little
over a third by stands < 100 years old in the 1890s (at the end of the reference period.
Most (58 %) of the forest stands in the subalpine landscape were > 150 years old, i.e.,
mature or old-growth (Romme et al. 2003). The spruce-fir landscape of the
Uncompahgre Plateau may have had a similar landscape structure during the reference
period, but it is important to note that proportions and patch sizes probably fluctuated
through time in response to climatic variability and variable fire frequency throughout
51
southwestern Colorado. See chapter 5 in Romme et al. (2003) for a discussion of sprucefir forests in the South Central Highlands Section which includes the Uncompahgre
Plateau.
RMLANDS State Transition Diagram for Spruce-Fir Forest
52
22. Spruce-Fir – Aspen Forest
Distribution.
This cover type is found on all aspects at the highest elevations on the Uncompahgre
Plateau. Its distribution overlaps that of the Spruce-Fir Forest; the reason why aspen is an
important component of some stands but not others is unknown. Similar communities are
elsewhere in the southern Rocky Mountain region (Peet 1988, Jamieson et al. 1996,
Johnston and Huckaby 2001, Romme et al. 2003).
Structure & Composition.
Spruce-Fir with Aspen Forest consists of sparse to dense stands of Picea engelmannii,
Abies lasiocarpa, and Populus tremuloides. A well-developed layer of shrubs, including
Vaccinium myrtillus, Rubacer parviflorum, Ribes montigenum, Sambucus microbotys,
and Lonicera involucrata is often present. A rich mixture of mesophytic herbs also is
often present, including Erigeron eximius, Geranium richardsonii, Ligusticum porteri,
Mertensia ciliata, Arnica cordifolia, Aquilegia elegantula, Pedicularis racemosa,
Orthilia secunda, Artemisia franserioides, Viola canadensis, Goodyera oblongifolia,
Fragaria vesca, Oreochrysum parryi, Lathyrus leucanthus, Pyrola minor, Maianthemum
stellatum, Luzula parviflora, Anticlea elegans, Bromopsis Canadensis, Carex geyeri, and
Osmorhiza depauperata (species list from J. Redders, San Juan National Forest, and
personal observations.
Species composition in this vegetation type is very similar to that of the spruce-fir
forest cover type, described above, with the exception that Potr is also an important
component of this type. Aspen is usually the dominant canopy species for several
decades after a major disturbance, but is gradually replaced by conifers over time. In late
successional stands, aspen may be represented only by scattered large canopy stems, with
little or no understory regeneration.
Stand Conditions and Successional Trends.
·
·
·
·
Stand Initiation (SI) – grasses, forbs, low shrubs, and moderate to dense cover of
trees (aspen much greater abundance than conifers) –seedlings/saplings (open
canopy), classify as Aspen for purposes of FRAGSTATS analysis and wildlife
habitat models … persists from stand age 0 until age 20-40
Stem Exclusion (SE) – ground cover of grasses, forbs, and shrubs; moderate to
dense cover of trees (aspen greater abundance than conifers) –pole size (closed
canopy), classify as Aspen for purposes of FRAGSTATS analysis and wildlife
habitat models … persists from stand age 20-40 until age 80-120
Understory Reinitiation (UR) – heterogeneous ground cover of grasses, forbs,
and shrubs; varying density of trees (conifers greater abundance than aspen) –
variable size classes (patchy closed canopy) … persists from stand age 80-120
until age 300-450
Shifting Mosaic (SM) – heterogeneous ground cover of grasses, forbs, and
shrubs; variable density of trees (conifers much greater abundance than aspen) –
variable size classes (patchy closed canopy) … persists from stand age 300-450
until the next stand-replacing disturbance
53
Effects of Natural Disturbances.
Wildfire. Fires tend to be high mortality, stand-replacing fires that initiate a process
of post-fire forest succession. High mortality fires kill large as well as small trees, and
may kill many of the shrubs and herbs as well, although below-ground organs of at least
some individual shrubs and herbs survive and re-sprout. Low mortality fires may
consume surface fuels (i.e., surface fire) and may result in the death of some overstory
trees, but the majority survive (i.e., mosaic fire).
·
·
·
·
Stand Initiation (SI) – a high mortality wildfire recycles the stand through the SI
condition while a low mortality wildfire maintains the condition
Stem Exclusion (SE) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire can either move the stand up to the UR
condition or maintain the stand in the SE condition
Understory Reinitiation (UR) – a high mortality wildfire returns the stand to the
SI condition while a low mortality wildfire can either move the stand up to the
SM condition or maintain the stand in the UR condition
Shifting Mosaic (SM) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire maintains the SM condition
Insects/Pathogens. Spruce beetle kills Engelmann spruce trees, especially in the
larger size classes (> ca. 8 inches dbh). Western spruce budworm gradually defoliates
subalpine fir trees and saplings of all sizes by killing terminal branch buds. Affected
trees may die after many years of repeated defoliation, or become susceptible to bark
beetle attack. None of these insects directly affect smaller individuals of spruce, nor do
they affect other tree species, shrubs, or herbs.
·
·
·
·
Stand Initiation (SI) – a high or low mortality outbreak of any of these insects
maintain the stand in the SI condition
Stem Exclusion (SE) – a high or low mortality outbreak of any of these insects
can either accelerate the stand up to the UR condition or maintain the stand in the
SE condition
Understory Reinitiation (UR) – a high or low mortality outbreak of any of these
insects can either accelerate the stand up to the SM condition or maintain the
stand in the UR condition
Shifting Mosaic (SM) –a high mortality outbreak of both insects returns the stand
to the SI condition while any other combination of outbreak will maintain the SM
condition
Reference Conditions and 20th Century Changes.
Prior to Euro-American settlement in the late 1800s, the spruce-fir landscape
consisted of a mosaic of successional stages developing after previous disturbances.
Some early successional stages were dominated by aspen, and other stands were almost
exclusively spruce and fir with little or no aspen, as described above for the spruce-fir
forest cover type. We have no specific information about relative proportions of
successional stages or about patch sizes and shapes on the Uncompahgre Plateau. A
study in the San Juan Mountains, ca. 100 km to the south, determined that about one-
54
tenth of the landscape may have been covered by young stands (< 50 years old), and a
little over a third by stands < 100 years old in the 1890s (at the end of the reference
period. Most (58 %) of the forest stands in the subalpine landscape were > 150 years old,
i.e., mature or old-growth (Romme et al. 2003). The spruce-fir landscape of the
Uncompahgre Plateau may have had a similar landscape structure during the reference
period, but it is important to note that proportions and patch sizes probably fluctuated
through time in response to climatic variability and variable fire frequency throughout
southwestern Colorado. See chapters 4 and 5 in Romme et al. (2003) for a discussion of
aspen and spruce-fir forests in the South Central Highlands Section which includes the
Uncompahgre Plateau.
RMLANDS State Transition Diagram for Spruce-Fir with Aspen Forest
55
23. Spruce Forest
Distribution.
note: this is the description copied exactly from Spruce-Fir Forest
This cover type is found on all aspects at the highest elevations on the Uncompahgre
Plateau. Similar communities are elsewhere in the southern Rocky Mountain region
(Peet 1988, Jamieson et al. 1996, Johnston and Huckaby 2001, Romme et al. 2003).
Structure & Composition.
note: this is the description copied exactly from Spruce-Fir Forest
Spruce-Fir Forest consists of sparse to dense stands of Picea engelmannii, and Abies
lasiocarpa, but without aspen. A well-developed layer of shrubs, including Vaccinium
myrtillus, Rubacer parviflorum, Ribes montigenum, Sambucus microbotys, and Lonicera
involucrate is often present. A rich mixture of mesophytic herbs also is often present,
including Erigeron eximius, Geranium richardsonii, Ligusticum porteri, Mertensia
ciliata, Arnica cordifolia, Aquilegia elegantula, Pedicularis racemosa, Orthilia secunda,
Artemisia franserioides, Viola canadensis, Goodyera oblongifolia, Fragaria vesca,
Oreochrysum parryi, Lathyrus leucanthus, Pyrola minor, Maianthemum stellatum,
Luzula parviflora, Anticlea elegans, Bromopsis Canadensis, Carex geyeri, and
Osmorhiza depauperata (species list from J. Redders, San Juan National Forest, and
personal observations.
Stand Conditions and Successional Trends.
note: this is the description copied exactly from Spruce-Fir Forest
·
·
·
·
Stand Initiation (SI) – grasses, forbs, low shrubs, and moderate to dense cover of
trees–seedlings/saplings (open canopy) … persists from 0 until age 30-200
Stem Exclusion (SE) – ground cover of grasses, forbs, and shrubs; moderate to
dense cover of trees–pole size (closed canopy) … persists from stand age 30-200
until age 150-300
Understory Reinitiation (UR) – heterogeneous ground cover of grasses, forbs,
and shrubs, varying density of trees–variable size classes, the older trees are from
the original cohort with a patchy closed canopy but there is an understory of
uneven aged trees … persists from stand age 150-300 until age 300-450
Shifting Mosaic (SM) – heterogeneous ground cover of grasses, forbs, and
shrubs; variable density of trees –variable size classes (patchy closed canopy) …
persists from stand age 300-450 until the next stand-replacing disturbance
Effects of Natural Disturbances.
Wildfire. Fires tend to be high mortality, stand-replacing fires that initiate a process
of post-fire forest succession. High mortality fires kill large as well as small trees, and
56
may kill many of the shrubs and herbs as well, although below-ground organs of at least
some individual shrubs and herbs survive and re-sprout. Low mortality fires may
consume surface fuels (i.e., surface fire) and may result in the death of some overstory
trees, but the majority survive (i.e., mosaic fire).
·
·
·
·
Stand Initiation (SI) – a high mortality wildfire recycles the stand through the SI
condition while a low mortality wildfire maintains the condition
Stem Exclusion (SE) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire can either accelerate the stand up to the
UR condition or maintain the stand in the SE condition
Understory Reinitiation (UR) – a high mortality wildfire returns the stand to the
SI condition while a low mortality wildfire can either accelerate the stand up to
the SM condition or maintain the stand in the UR condition
Shifting Mosaic (SM) – a high mortality wildfire returns the stand to the SI
condition while a low mortality wildfire maintains the stand in the SM condition
Insects/Pathogens. Spruce beetle kills Engelmann spruce trees, especially in the
larger size classes (> ca. 8 inches dbh). Western spruce budworm gradually defoliates
subalpine fire trees and saplings of all sizes by killing terminal branch buds. Affected
trees may die after many years of repeated defoliation, or become susceptible to bark
beetle attack. None of these insects directly affect smaller individuals of spruce, nor do
they affect other tree species, shrubs, or herbs.
·
·
·
·
Stand Initiation (SI) – a high mortality outbreak of both insects recycles the
stand through the SI condition while any other combination of insect outbreak
maintains the condition
Stem Exclusion (SE) – a high mortality outbreak of both insects returns the stand
to the SI condition while any other combination of insect outbreak can either
accelerate the transition up to the UR condition or maintain the stand in the SE
condition
Understory Reinitiation (UR) – a high mortality outbreak of both insects returns
the stand to the SI condition while any other combination of insect outbreak can
either accelerate the transition up to the SM condition or maintain the stand in the
UR condition
Shifting Mosaic (SM) – a high mortality outbreak of both insects returns the
stand to the SI condition while any other combination of insect outbreak will
maintain the SM condition
Reference Conditions and 20th Century Changes.
note: this is the description copied exactly from Spruce-Fir Forest
Prior to Euro-American settlement in the late 1800s, the spruce-fir landscape
consisted of a mosaic of successional stages developing after previous disturbances.
Some early successional stages were dominated by aspen, as described below for the
spruce-fir-aspen forest cover type, and other stands were almost exclusively spruce and
57
fir with little or no aspen. We have no specific information about relative proportions of
successional stages or about patch sizes and shapes on the Uncompahgre Plateau. A
study in the San Juan Mountains, ca. 100 km to the south, determined that about onetenth of the landscape may have been covered by young stands (< 50 years old), and a
little over a third by stands < 100 years old in the 1890s (at the end of the reference
period. Most (58 %) of the forest stands in the subalpine landscape were > 150 years old,
i.e., mature or old-growth (Romme et al. 2003). The spruce-fir landscape of the
Uncompahgre Plateau may have had a similar landscape structure during the reference
period, but it is important to note that proportions and patch sizes probably fluctuated
through time in response to climatic variability and variable fire frequency throughout
southwestern Colorado. See chapter 5 in Romme et al. (2003) for a discussion of sprucefir forests in the South Central Highlands Section which includes the Uncompahgre
Plateau.
RMLANDS State Transition Diagram for Spruce Forest
58
24. High-Elevation Sagebrush
Distribution.
This cover is found at middle to high elevations, especially in the northern part of the
Uncompahgre Plateau. Similar communities are elsewhere in the Colorado Plateau and
southern Rocky Mountain regions (Romme et al. 1993, Johnston and Huckaby 2001,
Romme et al. 2003).
Structure & Composition.
High-Elevation Sagebrush consists of sparse to dense shrublands of Artemisia
tridentata and Artemisia cana, with Purshia tridentata and other shrubs present in places,
plus sparse to dense grasses (e.g., Poa pratensis) and forbs (e.g., Vicia americana).
Species composition probably was altered by heavy grazing in the late 1800s and early
1900s, as described above for meadow vegetation. See Redders (2003a) for a more
thorough treatment of meadow and grassland vegetation in the South Central Highlands
Section which includes the Uncompahgre Plateau.
Stand Conditions and Successional Trends.
·
·
Herbs - Shrubs (HS) – low density of young, small shrubs and herbs, with
moderate cover of grasses & forbs … persists from stand age 0 until age 40-100
Shrubs - Herbs (SH) – high density of older large shrubs and herbs, with some
grasses & forbs … persists from stand age 40-100 until the next stand-replacing
disturbance
Effects of Natural Disturbances.
Wildfire. Fire kills the dominant shrubs, most of which must re-establish from seed.
Herbaceous plants lose above-ground biomass to fire, but most promptly re-sprout from
surviving below-ground organs.
·
·
Herbs - Shrubs (HS) – high mortality wildfire recycles the stand through the HS
condition while a low mortality wildfire maintains this condition
Shrubs - Herbs (SH) – high mortality wildfire sends the stand back to the HS
condition while a low mortality wildfire maintains this condition
Reference Conditions and 20th Century Changes.
Reference conditions in high-elevation sagebrush communities are virtually
unknown. Presumably the landscape was a mosaic of herb-dominated patches, where
fires or other disturbances had occurred recently, and shrub-dominated patches where no
disturbance had occurred recently. However, proportions of patch types and patch sizes
are not known for this area, and probably varied through time as disturbance frequencies
varied.
RMLANDS State Transition Diagram for High-Elevation Sagebrush
59
98. Agriculture??
99. Urban??
60
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61
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symposium proceedings; 13-15 June 2000; Grand Junction, CO. USDA Forest
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Romme, W.H., M. L. Floyd, and D.D. Hanna. 2003. Landscape condition analysis for the
South Central Highlands Section, southwestern Colorado & northwestern New
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