Ecosystem Management (EM) and Historical Range of Variability
(HRV): Brief introduction to general concepts to be further illustrated and
discussed in the applications part of the course.
Paradigms for a new approach to forestry (Kimmins ch. 18)
• Ecosystem management
• Adaptive management
• Zonation by use and value
• Variable retention
• Emulation of natural forest disturbance
Ecosystem management “… is management that acknowledges
the importance of human needs while at the same time
confronting the reality that the capacity of our world to meet
those needs in perpetuity has limits and depends on the
functioning of ecosystems.”
— Christensen et al. 1996 (Ecological Society of America).
“Ecosystem management means managing forests as a whole,
integrated systems rather than the frequently fragmented and
uncoordinated management for individual ecosystem
components and values—trees, wildlife, water, aesthetics, and
so on.”
--- Kimmins, J.P. 2004. Forest Ecology.
Guiding principles of ecosystem management from Christensen et al. 1996:
1.
2.
3.
4.
5.
Intergenerational sustainability
Explicit goals
Sound ecological models and understanding
Ecosystem complexity and connectedness
Recognition of the dynamic character of
ecosystems
6. Context and scale
7. Humans as ecosystem components
8. Adaptability and accountability
Adaptive management
•
Retain management flexibility
•
Monitor outcomes and compare with expected (hypothesized) outcomes
•
Incorporate new knowledge (research)
•
Forecast future scenarios…using multiple values, multiple scales, and
incorporating effects of disturbance and climatic variation.
Zonation
•
Spatial and/or temporal separation of certain forest values (e.g. timber vs.
recreation)
•
Percentages of area dedicated to different forest values are strongly influenced
by social and political factors.
•
Design of zonation systems requires sound understanding of disturbance
regimes and succession across a range of spatial scales.
Variable (attribute) retention
•
Renewal periods vary widely for different values (e.g. fast re-growth of timber vs.
slow recovery of old-growth quality for wildlife habitat).
•
In areas zoned for timber management, retain wildlife trees and habitat for
biodiversity.
•
Often difficult to balance with economic constraints and safety issues.
Emulation of natural forest disturbance (ENFD)
•
Maintenance of the historical (natural) range of ecosystem conditions.
•
Consistent with a “coarse filter” rather than a “fine filter” approach to sustain
biodiversity and ecosystem function.
•
Incorporating natural disturbance (exploiting it, sometimes guiding it) is usually
more cost effective than suppressing it.
•
Use of ENFD implies an understanding of Historical Range of Variability (HRV) of
ecosystems.
Historic Range of Variability (HRV) of Ecosystems
What is HRV and what is its role in ecosystem-based management?
For resource managers, it is important to know the range of critical
ecological processes and conditions that have characterized particular
ecosystems over specified time periods and under varying degrees of
human influences.
An understanding of how ecosystems functioned and sustained
themselves in the absence of major human modification of ecological
patterns and processes provides a concrete model of ecosystem
integrity.
Why are HRV studies needed?
-- An ecological perspective:
“Human-generated changes must be constrained because nature has functional,
historical, and evolutionary limits. Nature has a range of ways to be, but there is a limit
to those ways, and therefore, human changes must be within those limits.”
Pickett et al. 1992. The new paradigm in ecology.
Why are HRV studies needed?
-- A resource management perspective:
“Awareness and understanding of disturbance ecology and the role disturbance plays in
ecosystem dynamics...is essential in understanding the consequences of management
choices. The more we attempt to maintain an ecosystem in a static condition, the less
likely we are to achieve what we intended.”
Averill et al. 1995 (USDA Forest Service
document.
Challenges and limitations to ENFD and HRV approaches
•
Zonation—not compatible with all values.
•
Large infrequent disturbances (LIDs) pose special problems (Mt. St. Helens, YNP
1988).
•
What is the appropriate historical period?
•
Knowledge of HRV is often inadequate.
•
Equilibrium models (perceptions) tend to bias expectations.
•
Climatic variation may change everything…but how does HRV help us
understand the effects of current climate change?
How is ecological restoration related to ENDF and HRV?
•
Object oriented restoration
–
Tries to recreate a static model of the past
–
•
Stresses patch size, percentage cover, tree density, percentage of
landscape in different seral stages.
Process-oriented restoration
–
Allows the processes (fire, insect outbreaks) that shaped the landscape to
continue.
Which approach is more likely to attain a set of management goals in a cost effective
way?
METHODS OF ANALYZING VEGETATION CHANGE PART
TWO:
Methods relevant to assessing historic range of variability of vegetation
The focus here will be on methods that are potentially useful in documenting changes in
vegetation patterns and identifying the causes or processes involved in these changes at
time scales of a few decades to several centuries. Although fossil records (both macrofossils and micro-fossils) are important in documenting vegetation changes, the typical
millennial time scale of fossil studies is beyond the scope of this course. An introductory
level source on all of these methods is: D. Egan and E.A. Howell. 2001. The Historical
Ecology Handbook: A Restorationist’s Guide to Reference Ecosystems. Island Press.
A. Short-term historical methods
1. Written documentary (textual) sources include 1) early accounts of European
explorers (typically 16th to 18th centuries); 2) archival documents from colonial
authorities (both civilian and religious); 3) pre-20th century travelers; 4) Native
American sources (e.g. “captivity narratives” from early colonists; transcriptions of
Native American oral traditions) notes and reports of 19th century ethnologists; 5)
early scientific and surveying expeditions; and 6) local histories.
Useful for gross changes, but reliability for subtle change is doubtful.
Discuss: How can the reliability of historical sources be evaluated? How can
reporter bias be assessed?
2. Historical maps of vegetation
Quality and utility are highly variable.
Issues that must be addressed:
a. Spatial scale-- is the map to scale?
b. Positional accuracy-- how can that be assessed?
c. Classification comparability— are the vegetation types comparable in level of
detail to modern classifications?
d. Classification accuracy— how can reliability of the historical map be assessed?
3. Terrestrial photographs
Only available after c. 1850.
If available, excellent for documenting gross changes and generating hypotheses
to explain the changes (especially when combined with other data).
Problems:
a. Locations may not be representative (e.g. along roads, railroads)
b. Changes are not easily quantified
c. Both maps and photographs are only “snapshots” in time and may not be
representative of landscape conditions over longer time scales of decades or
centuries.
4. Aerial photographs/remote sensing images
Excellent for quantifying changes in cover type.
Problems:
a. Aerial photographs older than c. 1935 are rare.
b. Rarely allow identification of individual species.
5. Re-measurement of previously surveyed areas
a. Old vegetation surveys for earlier ecological studies or timber inventories.
b. Use of General Land Office surveys
B. Monitoring of permanent plots (including experimental plots such as exclosures)
Generally, the best source of data but records are scarce and usually short.
Considerations in installing permanent plots:
1. High cost—labor intensive, maintenance costs.
2. Location:
representative sites;
objective vs. subjective placement of plots to test particular hypotheses;
accessibility and ease of re-location by future works;
long-term protection of the site.
3. Potential parameters to be measured or recorded:
tree species identification and permanent markers on trees;
diameter at breast height (dbh; accuracy);
tree locations (x and y coordinates);
tree ages and ring width samples for growth measurements;
tree heights;
understory composition, tree seedling populations (often with smaller
plots);
importance of clear measurement instructions (e.g. size class definitions
of seedling vs. tree, measurement of bifurcated trunks, how to measure
dbh of trees with buttresses, etc.)
4. Experimental permanent plots
if the cost of using permanent plots is justified, then maximum value is
usually obtained by making the permanent plots part of an experimental
design (e.g. trenching experiments, silvicultural treatments, animal
exclosures).
Brief Introduction to Formation of Annual Tree Rings
•
Sources on Tree-Rings
–
http://www.ltrr.arizona.edu/treerings.html
–
http://web.utk.edu/~grissino/ltrs/lectures.htm
Key Definitions
•
Cambium: the growing (generative) layer between the xylem and phloem.
•
Xylem: principle strengthening and water conducting tissue of the stem, roots, and
branches.
•
Tracheids are elongated cells in the xylem, serving in the transport of water.
•
Phloem: inner bark, principal function to distribute manufactured foodstuffs.
•
Sapwood: outer core of xylem (water conducting)
•
Heartwood: inner core of xylem (usually plugged, often darker)
•
Early wood (spring wood) vs. latewood (summer wood):
•
In a conifer—
earlywood appears light in color cells have thin walls, large diameter
latewood appears dark in color cells have thick walls, small diameter
Fire History Methods—brief introduction
Two Alternatives: Fire-scar method and
Stand-origin method
Terminology for Fire-scar method:
Mean Composite Fire Interval
= mean interval between successive fire years in a designated area;
CFI can include all fire years within the area or can be “filtered” (e.g.
years with at least 2, 3, etc. fire-scars)
1)
Disadvantages of composite MFI–
It is highly dependent on size of the search area;
2) It does not discriminate between small versus large fires or even between
overlapping and non-overlapping fires (but this can be partially resolved by identifying
years of high % fire scars or by mapping individual trees).
3) When fire years are infrequent, MFI changes greatly when only slight changes are
made in the definitions of periods such as Native American, Euro-American Settlement,
and Fire Suppression Periods.
4) Composite MFI is also dependent on the number of trees sampled (the number of
detected fires rises steeply until a sample size of c. 10 trees has been used, but this is
only a rule of thumb).
Stand-origin method:
Based on mapping post-fire cohorts
What are the disadvantages?