Geological Society of America Fall 2007 Meeting, Denver, Colorado
Session No. 53 Geomorphology (Posters)
Riparian Plant Distribution in the Luckiamute River Basin, Central Oregon Coast Range: Preliminary Analysis of
Geomorphic and Anthropogenic Controls on Adventive Species Propagation in an Unregulated Watershed
Taylor, Stephen B. 1, Dutton, Bryan E.2, Noll, Katherine1, and Pirot, Rachel3, (1) Earth and Physical Science Dept, Western Oregon University,
Monmouth, OR 97361, taylors@wou.edu, (2) Biology Dept, Western Oregon University, Monmouth, OR 97361, (3) Dept. of Geology, Portland State
University, Portland, OR 97207
1. ABSTRACT
A
Disturbance by geomorphic and anthropogenic processes affects
riparian substrate, nutrient levels, canopy shading, and hydrology. As such,
fluvial systems commonly serve as conduits for the dispersal of exotic plant
species. This study involves spatial analysis of vascular plant distribution in
the riparian understory of the Luckiamute River basin, central Oregon Coast
Range.
Preliminary results are used to decipher geomorphic and
anthropogenic controls on adventive species propagation in an unregulated
watershed.
Over 1700 m2 of riparian understory was surveyed using 1- by 100-m
transects oriented perpendicular to the active channel, with 20 survey
stations irregularly spaced (Davg = 5.1 km) along the lower 100 km of the
drainage (Ad = 815 km2). Vascular plant species were identified in each
transect with observations on distance from channel, cover area, frequency
of occurrence, origin, canopy composition, and light intensity. The majority of
survey stations were located on incised floodplain surfaces characterized by
riparian tree cover, silty-clay loams, and slopes less than 10%. Survey
results are summarized as follows: No. of Adventive Species = 55; No. of
Native Species = 75; Adventive Cover = 26.7%; Native Cover = 12.8%;
Native:Adventive Ratio = 2.1. The two most common adventives are Rubus
armeniacus (Himalayan blackberry) and Phalaris arundinacea (Reed
canarygrass). Polygonum cuspidatum (Japanese knotweed) has limited
frequency, but ranks in the 95th percentile of total invasive area. The most
abundant native species include Rubus leucodermis (Blackcap),
Symphoricarpos albus (Snowberry), Urtica dioca (Stinging nettle), and
Polystichum munitum (Sword fern).
Distribution analysis provides a framework for positing mechanisms of
adventive plant dispersion.
Longitudinally, R. armeniacus and P.
arundinacea are ubiquitously distributed throughout the lower watershed,
while P. cuspidatum is restricted to upper reaches. Transverse to the
floodplain, P. cuspidatum is limited in occurrence to less than 30 m from the
channel, while P. arundinacea and R. armeniacus are common throughout.
Results suggest that hydrochory is the primary dispersal mechanism for the
former two species, while mixed modes apply to the latter. A combination of
geomorphic (flooding) and anthropogenic disturbance (timber harvesting)
processes result in substrate alteration and canopy gaps, thus diminishing
barriers to exotic plant colonization.
2. INTRODUCTION
Invasive plant species in western Oregon are a pervasive problem that
disrupt native habitats and create annual economic losses of millions of
dollars for public and private landowners (Oregon Department of Agriculture,
2001). Nationwide, the United States experiences annual losses of over
$130,000,000.00 due to non-native species (Pimentel and others, 2000).
Vegetative disturbance of natural ecosystems by geomorphic and
anthropogenic processes affect soil substrate conditions, nutrient availability,
canopy shading (solar influx), and riparian hydrology. The most abundant
concentrations of invasive species are typically associated with disturbed
zones that have been altered by human activity. As such, disturbed zones on
the landscape act as primary conduits for the dispersal of non-native species
(Pabst and Spies, 1998). Understanding the controls on spatial distribution of
invasive plants in the context of disturbance regime is critical for designing
effective watershed conservation and restoration plans.
The purpose of this research was to conduct a reconnaissance survey to
delineate associations between geomorphic and anthropogenic disturbance
regimes, and distribution patterns of invasive plant species in the Luckiamute
Watershed of western Oregon (Figures 1 and 2).
From Luckiamute Watershed Council
Figure 1. Location map of the Luckiamute Watershed, western Oregon.
5. RESULTS
A. Generalized Map of Surficial Geology
B
HillslopeColluvial
Qrc2
Qau
Valley
FloorFluvial
Qrc2
Qrc2
Geomorphic
Regime
Qrc1
Qau
Qrc2
Qau
Qrc1
Qau
Hal
Qff2
Holocene alluvium
Hal
Qff2 Missoula flood deposits
(13.5-12 ka)
Figure 2. A. Oblique aerial photograph overlooking a portion of the Luckiamute
Basin. View is to the west towards Coast Range. Note agricultural landuse in
lowlands and forestry management in the uplands. B. Photo of the main stem of the
Luckiamute River channel at bankfull stage Luckiamute River at Helmick State Park;
3800 cfs on March 27, 2005. Note riparian vegetation along channel-margin
floodplains, the focus of this study.
Qau
Qau Quaternary alluvium
undifferentiated
Qrc2
Qau
Qtg
Qtg Quaternary terrace
gravel
Qrc1
N
Qrc1 Quaternary residuumcolluvium (low relief hillslopes)
0
5 km
Qrc2 Quaternary residuumcolluvium (high relief hillslopes)
B. Generalized Geomorphic Cross Section (Helmick State Park)
SW
NE
Luckiamute River
(incised channel)
3. PHYSIOGRAPHIC SETTING
Middle
terrace
(>12 ka)
3 A. Geology and Geomorphology
The Luckiamute River comprises a portion of the Willamette basin in
west-central Oregon (Figure 1). This seventh-order watershed (sensu
Strahler, 1957) drains eastward from the Coast Range into the Willamette
River and occupies a total drainage area of 815 km2. Land surface
elevations range from 46 m (150 ft) at the confluence with the Willamette
River to 1016 m (3333 ft) at Fanno Peak. The Luckiamute has an average
gradient of 3 m/km, a total stream length of 90.7 km, and an average basin
elevation of 277 m (910 ft) (Rhea, 1993; Slack and others, 1993).
Lithostratigraphic units are grouped into four spatial domains in the
Luckiamute, these include the Siletz River Volcanics domain (south), the
Tyee domain (west-southwest), the Yamhill-Intrusive domain (northnorthwest), and the Spencer-Valley Fill domain (east). Geomorphic systems
are divided into a valley-floor regime to the east and hillslope-colluvial regime
to the west (Figure 3). Hillslope landforms and colluvial processes dominate
the Siletz River, Tyee, and Yamhill-Intrusive domains, while fluvial landforms
and alluvial processes are characteristic of the Spencer-Valley Fill domain.
The lower Luckiamute is characterized by a mix of alluvial stratigraphic
units and geomorphic surfaces.
Landforms include active channels,
floodplains, fill terraces, and strath-pediment surfaces (McDowell, 1991). In
addition to these fluvial landforms, the lower Luckiamute is also associated
with swaths of low-relief colluvial hillslopes supported by the Spencer
Formation (Figure 3). Pleistocene through Holocene terrace development
records a complex history of base level fluctuation, internal erosiondeposition cycles, and glacial-outburst floods (Missoula Floods) from the
Columbia River system. The active channel of the lower Luckiamute is
incised 8 to 9 m below the floodplain, with higher level terrace surfaces at 12
to 15 m above mean annual stage (Reckendorf, 1993). The higher-level
terrace surfaces are covered with rhymically-bedded, silty slack-water
deposits of the Willamette Formation (Missoula Flood deposits; 13.5-12 Ka).
These late Pleistocene surfaces are inset with lower terrace and floodplain
deposits that are predominantly Holocene in age (post-Missoula Flood; <12
Ka) (Figure 3; O'Connor and others, 2001).
Low
terrace
(<12 ka)
25
High
terrace
(>12.0 ka)
p
lo
s
de
Si
e
Older Pleistocene
gravel (not exposed)
0
5 A. Understory Vegetation
Spencer Formation (bedrock)
0
500
meters
Figure 3. Generalized geomorphic map of the Luckiamute Watershed
(after O’Connor and others, 2001).
4. METHODS
Riparian plant surveys were conducted at 20 sites using a 1-m2
sampling grid along survey lines oriented transverse to the active channel.
Field and analytical procedures following those prescribed by Elzinga and
others (1998) (Figures 4 and 5). Sample sites were confined to wooded
riparian zones within a 100-m buffer along the 100-year floodplain of the
channel system. Final site selection was determined on the basis of
logistical access, property owner permission, and position in canopy-covered
riparian zone. All understory and overstory species were identified along the
transects and light measurements were collected in the 400 to 700 nm
wavelength range using a Quantum light meter. GPS positions and general
geomorphic observations were recorded as well.
Western
Oregon
University
Over 1700 m2 of riparian understory was surveyed using 1- by 100-m
transects oriented perpendicular to the active channel, with 20 survey
stations irregularly spaced (Davg = 5.1 km) along the lower 100 km of the
drainage (Ad = 815 km2). 170 vascular plant species were identified in the
understory (Table 1). The majority of survey stations were located on incised
floodplain surfaces characterized by riparian tree cover, silty-clay loams, and
slopes less than 10%. Survey results are summarized as follows: No. of
Adventive Species = 55; No. of Native Species = 75; Adventive Cover =
26.7%; Native Cover = 12.8%; Native:Adventive Ratio = 2.1 (Table 2). The
two most common adventives are Rubus armeniacus (Himalayan
blackberry) and Phalaris arundinacea (Reed canarygrass). Polygonum
cuspidatum
(Japanese
knotweed) inhas
limited
frequency,
but ranks
in the
Summary of Plant
Species Encountered
Riparian
Understory
– Luckiamute
Watershed
95th percentile of total invasive area (Figure 6). The most abundant native
species
include
leucodermis
(Blackcap),
Total
No. of Species
Encountered Rubus
170
Most Common Species Encountered
in Greater thanSymphoricarpos
70% of Transects (total n = 20) albus
Total No. of Invasive Species
55
(Snowberry),
nettle), Blackcap
and Polystichum munitum
Total
No. of Native Species Urtica75 dioca
Rubus(Stinging
leucodermus
90% native
Total No. with No Origin Data
40
Rubus armeniacus
Himalaya blackberry
85% introduced
(Sword
fern) (Figure 32.4%
7). Symphoricarpos albus
Percent
Invasives
Snowberry
85% native
Percent Natives
Percent Unknown Origin
Native/Invasive Ratio
44.1%
23.5%
1.4
Urtica dioca (gracilis)
Corylus cornuta (californica)
Phalaris arundinacea
Polystichum munitum
Stinging nettle
Western hazel
Reed canarygrass
Sword fern
Table 1. Summary of plant species encountered in the riparian understory,
Luckiamute Watershed.
Abies grandis Grand fir
Acer circinatum Vine maple
Acer macrophyllum Big-leaf maple
Achlys triphylla Vanillaleaf
Actaea rubra Baneberry
Adenocaulon bicolor Pathfinder
Alnus rubra Red alder
Amelanchier alnifolia Service berry
Anagallis arvensis Scarlet Pimpernel
Anemone deltoidea White windflower
Anthemis cotula Dogfennel
Apiaceae Umbel family
Aquilegia formosa Columbine
Arctium minus Common burdock
Asarum caudatum Wild ginger
Asteraceae Aster family
Athyrium felix-femin Lady fern
Berberis aquifolium Tall Oregon-grape
Berberis nervosa Mountain Oregon-grape
Bidens sp. Beggar's ticks
Brachypodium sylvaticum False brome
Brassicaceae Mustard family
Carex sp. Sedge
Centaurea xpratensis Meadow knapweed
Chenopodium album Lamb's quarters
Cicuta douglasii Western water hemlock
Cirsium arvense Canada thistle
Cirsium vulgare Bull thistle
Claytonia sibirica Candy flower
Clematis ligusticifolia Wild Clematis
Convovulus arvensis Bindweed
Cornus sericea Creek dogwood
Corylus cornuta (californica) Western hazel
Crataegus douglasii Western hawthorn
Crataegus sp. Hawthorn
Daucus carota Wild carrot
Delphinium trolliifolium Wood larkspur
Dicentra formosa Bleeding-heart
Digitalis purpurea Foxglove
Dipsacus fullonum Wild teasel
Epilobium angustifolium Fireweed
Epilobium ciliatum Willow-herb
Epilobium sp. Willow-herb
Equisetum arvense Common horsetail
Equisetum sp. Horsetail
Ericaceae Heath family
Euphorbia sp. Spurge
Fabaceae sp. Legume family
Fragaria vesca Wood strawberry
Fraxinus latifolia Oregon ash
Galium aparine Bedstraw
Galium sp. Bedstraw
Galium triflorum Fragrant bedstraw
Gaultheria shallon Salal
Geranium pusillum Small-flowered Geranium
Geranium robertianum Herb Robert
Geranium sp. Geranium
Glechoma hederacea Ground ivy
Gnaphalium sp. Cudweed
Goodyera oblongifolia Rattlesnake plantain
Hedera helix English ivy
Helianthus sp. Sunflower
Heracleum lanatum Cow parsnip
Heuchera micrantha Small-flowered alum-root
Heuchera sp. Alum-root
Hieracium aurantiacum Orange hawkweed
Hieracium sp. Hawkweed
Holodiscus discolor Ocean spray
Humulus lupulus Common hop
Hypericum perforatum St. John's wort
Hypochaeris radicata False dandelion
Ilex opaca American holly
Impatiens sp. Touch-me-not
Juncaceae sp. Rush family
Kickxia elatine Sharppoint Fluellin
Lactuca muralis Wall lettuce
Lactuca serriola Prickly lettuce
Lamiaceae sp. Mint family
Lapsana communis Nipplewort
Lathyrus sp. Pea
Leucanthemum vulgare Oxeye daisy
Lilliaceae sp. Lily family
Lotus corniculatus Bird's-foot trefoil
Lotus sp. Trefoil
Lysichiton americanum Yellow skunk cabbage
Maianthemum dilatatum Wild lily-of-the-valley
Maianthemum racemosus Large false Solomon's
seal
Maianthemum sp. False Solomon's seal
Malus sp. Apple
Marah oreganus Old man-in-the-ground
Melilotus sp. Sweet-clover
Melissa officinalis Lemon balm
Mentha xpiperita Peppermint
Mitella sp. Mitrewort
Oemleria cerasiformi sIndian peach
Osmorhiza berteroi Common sweet cicely
Oxalis oregana Oregon wood-sorrel
Penstemon sp. Penstemon
Phalaris arundinacea Reed canarygrass
Physocarpus capitatus Ninebark
Plantago aristata Long-bracted plantain
Plantago lanceolata English plantain
Plantago major Common plantain
Plantago sp. Plantain
Poaceae sp. Grass family
Polygonaceae Knotweed family
Polygonum cuspidatum Japanese knotweed
Polygonum lapathifolium Dock-leaved smartweek
Polypodium glycyrrhiza Licorice fern
Polystichum munitum Sword fern
Prosartes sp. Fairy bells
Prunella vulgaris Self-heal
Prunus sp. Cherry
Prunus virginiana Western chokecherry
Pseudostuga menziesii Douglas-fir
Pteridium aquilinum Western bracken fern
Quercus garryana Oregon white oak
80% native
75% native
75% introduced
70% native
Ranunculus sp. Buttercup
Rhamnus purshiana Cascara
Ribes sp. Gooseberry
Rosa eglanteria Sweetbriar
Rosa gymnocarpa Wood rose
Rosa nutkana Common wild rose
Rosa sp. Rose
Rubiaceae Madder family
Rubus armeniacus Himalaya blackberry
Rubus laciniatus Evergreen blackberry
Rubus leucodermus Blackcap
Rubus parviflorus Thimbleberry
Rubus spectabilis Salmonberry
Rubus ursinus Wild blackberry
Rumex acetosella Red sorrel
Rumex crispus Curly dock
Rumex sp. Dock
Salix sp. Willow
Sambucus racemosa Red Elderberry
Sambucus sp. Elderberry
Sanicula sp. Snake-root
Saxifragaceae Saxifrage family
Scirpus sp. Bulrush
Scutellaria lateriflora Common skullcap
Senecio jacobaea Tansy ragwort
Senecio sp. Groundsel
Senecio vulgaris Common groundsel
Sherardia arvensis Field madder
Solanum dulcamara Bittersweet nightshade
Solanum nigrum Europena black nightshade
Solanum sp. Nightshade
Soliva sessilis Field burrweed
Sonchus oleracea Common sow thistle
Sonchus sp. Sow thistle
Spiraea douglasii Douglas' Spiraea
Stachys cooleyae Giant hedge-nettle
Symphoricarpos albus Snowberry
Syntheris reniformis Spring queen
Tellima grandiflora Fringe-cups
Thalictrum sp. Meadow-rue
Toxicodendron diversilobum Poison oak
Trientalis latifolia Western starflower
Trifolium repens White clover
Trifolium sp. Clover
Trifolum vesiculosum Arrowleaf clover
Trillium sp. Trillium
Tsuga heterophylla Western hemlock
Urtica dioca (gracilis) Stinging nettle
Vaccinium sp. Huckleberry
Verbascum thapsus Common mullein
Veronica sp. Speedwell
Viola glabella Wood violet
Viola sp. Violet
3 B. Vegetation and Land Use
A
The Coast Range portion of the Luckiamute watershed lies in the Tsuga
heterophylla Zone of Franklin and Dyrness (1988). Dominant forest species
include Pseudotsuga menziesii (Douglas fir), Tsuga heterophylla (western
hemlock), and Thuja plicata (western red cedar), with lesser occurrence of
Abies grandis (grand fir). These species formed part of the classic old
growth timber stands that were logged extensively in the Pacific Northwest
during the early 1900's. Lower reaches of the Luckiamute watershed lie in
agricultural crop and pasture land, with local patches of mixed Quercus
garryana (Oregon white oak) and urban mosaic species.
Since European settlement, the dominant economic activities in the
Willamette Valley have centered on agriculture in the lowlands and timber
harvesting in upland forests. Over the past several decades, industrialization
and rapid population growth have resulted in significant impact to the habitat
of the region. A large portion of the upper Luckiamute is owned by private
timber companies and 67% of the watershed classified as forest. In contrast,
the eastern valley section is comprised of a mix of agricultural lands (15% of
total), native vegetation (3%), and urban development (1%) (Urich and
Wentz, 1999). Primary commodities in the agricultural zones include grass
seed, wheat, hay, oats, and mixed crops (clover, sweet corn, mint, alfalfa,
filberts) (Wentz and others, 1998).
B
Figure 4. Locations of plant-survey transects in the Luckiamute Watershed.
C
Figure 6. Field photos showing the
most common invasive plant cover
(by area) encountered in transects.
A. Rubus armeniacus (Himalayan
blackberry). B. Phalaris arundinacea
(Reed canarygrass); C. Polygonum
cuspidatum (Japanese knotweed).
Figure 5. Photos showing 1-m by 100-m quadrat methodology used in plant surveys.
A
B
C
D
(Discussion – Cont.)
restricted to upper reaches. Transverse to the floodplain, Polygonum
cuspidatum (Japanese knotweed) is limited in occurrence to less than 30 m
from the channel, while Phalarus arundinacea (Reed canarygrass) and
Rubus armeniacus (Himalayan blackberry) are common throughout. It is
clear from the survey data that Rubus armeniacus (Himalayan blackberry) is
a generalist that is ubiquitously distributed in all portions of the watershed
system. Phalarus arundinacea (Reed canarygrass) is more extensively
distributed across the floodplain in downstream reaches, and becomes
restricted nearer the channel in upstream sectors. Figures 10A, 10B, and
10C further demonstrate these transverse spatial patterns.
While preliminary in nature, results from the Luckiamute study suggest
that hydrochory is the primary dispersal mechanism for Polygonum
cuspidatum (Japanese knotweed), while mixed modes apply to Rubus
armeniacus (Himalayan blackberry) and Phalarus arundinacea (Reed
canarygrass). The working hypothesis is that a combination of geomorphic
(flooding) and anthropogenic disturbance (timber harvesting) processes
result in substrate alteration and canopy gaps, thus diminishing barriers to
exotic plant colonization.
Adventive plant species are problematic for both native and agricultural
plant communities as they can compete for resources and displace
competitors. Local extirpation of native plant species has obvious impacts
on wildlife and natural habitats. Competition between plant species is a part
of any habitat, but introduction of non-native species disrupts relationships
evolved among native plants and their communities within those specific
habitats. The ecological impacts of adventive vegetation on species diversity
in the Luckiamute is notably demonstrated in Figure 11. This plot relates
species richness (total no. of invasive and native understory species per m2)
to percent cover of the top three invasives (Himalayan blackberry, Reed
canarygrass, Japanese knotweed). The upper envelope defines the limiting
association of species richness by percent cover of invasives.
Western Oregon
University
Figure 7. Field photos showing the most common native plant cover (by area)
encountered in survey transects. A. Rubus leucodermis (Blackcap); B.
Symphoricarpos albus (Snowberry); C. Urtica dioca (gracilis) (Stinging nettle); D.
Polystichum munitum (Sword fern). Refer to Table 2 for summary of invasive and
native plant distribution statistics in the Luckiamute Watershed.
Table 2. Plant survey summary statistics, Luckiamute Watershed.
Figure 10A. Plot of Himalayan blackberry (Rubus armeniacus) cover along survey
traverses perpendicular to the active channel. Data are tallied from all 1-m2 quadrats
at the 20 survey locations shown in Figure 4.
Invasive Plant Summary Statistics – Luckiamute Watershed
I.
Survey / Transect Data
Location Criteria = Logistical / property access + transects located in forested riparian canopy,
surveyed for up to 100 m perpendicular to active channel reach.
Total No. of Transects:
Length of Transects:
Width of Transects:
Average Area per Transect:
Total Survey Area:
Average Transect Spacing:
II.
20
29-100 m
1m
89 m2
1785 m2
5.1 km
Geomorphic Setting of Survey Transects
Total Channel Length Sampled at Discrete Intervals:
Elevation Range:
Slope Range:
Average Slope:
Transect Geomorphic Setting
Wide (>100 m) Floodplain-Low Terrace (Alluvial Fill):
Soil: Silty Clay Loam
Landuse: Ag., Grazing, Woodlot
Narrow (<50 m) Floodplain (Sedimentary Bedrock):
Soil: Silt Loam
Landuse: Ag., Grazing, Woodlot
Narrow (<50 m) Floodplain-Hillslope (Sed. Bedrock):
Soil: Silty Clay Loam
Landuse: Historic Forestry
No. of Transects within Missoula Flood Zone:
No. of Transects Above Missoula Flood Zone:
107 km
48-235 m
< 1% to 27% (Avg. < 10%)
8.5%
Figure 8. Map showing spatial distribution of the top three invasive cover plants in
the riparian zone of the Luckiamute basin.
15
1
4
18
2
Figure 11. Plot of species richness (total no. of invasive and native understory
species per m2) vs. percent cover of the top three invasives (Himalayan blackberry,
Reed canarygrass, Japanese knotweed). The upper envelope line defines the
association between the limit of species richness by percent cover of invasives.
Data are tallied from all 1-m2 quadrats at the 20 survey locations shown in Figure 4.
III. Overstory / Riparian Forest Canopy
Riparian canopy dominated by Fraxinus latifolia (Oregon ash; 60% of transects), Acer
macrophyllum (Big leaf maple; 55% of transects), Corylus cornuta subsp. Californica (Western
hazel; 30% of transects), Cornus sericea (Creek dogwood; 25% of transects), Pseudostuga
menziesii (Douglas-fir; 25% of transects).
7. CONCLUSION
Canopy comprised of lesser amounts of Salix sp. (Willow; 20%), Acer circinatum (Vine maple;
15%), Alnus rubra (Red alder; 15%), and Quercus garryana (Oregon white oak; 15%).
IV.
Understory Riparian Analysis
Total No. of Species Encountered:
Total No. of Invasive Species:
Total No. of Native Species:
Total No. of Genus-Level Identification:
Ratio No. Natives / No. Invasives:
Total Area Invasive (sq. m) :
Total Area Natives (sq. m):
Total Area Genus-Level (sq. m):
Total Area No Cover (sq. m):
Ratio Area Natives / Area Invasives:
Figure 10B. Plot of Reed canarygrass (Phalaris arundinacea) cover along survey
traverses perpendicular to the active channel. Data are tallied from all 1-m2 quadrats
at the 20 survey locations shown in Figure 4.
170
55
75
40
1.4
228
477
78
1002
26.7%
12.8%
4.4%
56.1%
2.1
Most Commonly Encountered Native Species
Rubus leucodermus (Blackcap):
Symphoricarpos albus (Snowberry):
Urtica dioca (gracilis) (Stinging nettle):
Corylus cornuta (californica) (Western hazel):
Polystichum munitum (Sword fern):
90% of Transect Locations
85% of Transect Locations
80% of Transect Locations
75% of Transect Locations
70% of Transect Locations
Areal Coverage of Native Species (Top 8; )
5 B.
Rubus leucodermus (Blackcap):
Symphoricarpos albus (Snowberry):
Polystichum munitum (Sword fern):
Urtica dioca (gracilis) (Stinging nettle)
Corylus cornuta (californica) (Western hazel):
Rubus spectabilis (Salmonberry):
Rubus parviflorus (Thimbleberry):
Berberis
nervosa
(Mountain Oregon-grape):
Invasive
Plant
Distribution
Most Commonly Encountered Invasive Species
107.2 sq. m
76.0 sq. m
66.4 sq. m
33.8 sq. m
27.1 sq. m
24.7 sq. m
16.8 sq. m
13.1 sq. m
Distribution analysis provides a framework for positing mechanisms of
Rubus armeniacus (Himalaya blackberry):
85% of Transect Locations
adventive Phalaris
plant arundinacea
dispersion.
Two
spatial
variables
are
considered:
(Reed canarygrass):
75% of
Transect
Locations (1)
longitudinalSolanum
distribution
invasives
along the channel
network,
and (2)
dulcamaraof(Bittersweet
nightshade):
60% of Transect
Locations
arvense across
(Canada thistle):
40% of Transectto
Locations
transverseCirsium
distribution
the riparian zone, perpendicular
the active
channel. Note:
Figure
8 is a cuspidatum
distribution
map showing
theencountered
occurrence
of the
Polygonum
(Japanese
knotweed) only
in 15%
(3/20)top
of
transectspecies
locations, in
but the
one ofwatershed.
the top 3 invasives
in terms of
arealare
coverage,
see below)
three invasive
Quadrat
data
re-plotted
in
Figure
9 Coverage
according
to distance
upstream
the area
riverencountered)
mouth (km) and
Areal
of Invasive
Species (Top
3; 86% offrom
all invasive
transverseRubus
distance
across the floodplain (m).
armeniacus (Himalaya blackberry):
116.7 sq. m
Longitudinally,
Rubus (Reed
armeniacus
(Himalayan blackberry)
and Phalarus
Phalaris arundinacea
canarygrass):
63.8 sq. m
Polygonum
(Japanese
15.9 sq. m throughout the
arundinacea
(Reedcuspidatum
canarygrass)
areknotweed):
ubiquitously distributed
lower watershed, while Polygonum cuspidatum (Japanese knotweed) is
Annual economic losses and habitat degradation by invasive plant
species in the United States are well documented. Understanding the
controls on spatial distribution of invasives is critical for designing effective
watershed conservation and restoration plans. To this end, this study: (1)
provides important baseline data on the dispersion of non-native invasive
plant species in western Oregon, (2) provides a framework for discerning
patterns of invasion, (3) provides a methodology for assessing susceptibility
of land areas to invasion based on select comparator species, and (4)
contributes to a more thorough understanding of the basic biology of a
adventive plant species in the region. The results of this preliminary work
will form the basis of more extensive studies in the region and have
potential use for development of larger scale predictive models of invasive
plant dispersion.
8. ACKNOWLEDGMENTS
Figure 9. Plot of dominant invasive plant species distribution according to
transverse distance across the riparian zone (m, X axis) and distance in the
channel system upstream from the mouth of the basin (km, Y axis). Symbols are
the same as those used in Figure 7.
This project was generously funded by the The Oregon Community
Foundation and the Western Oregon University Faculty Development Fund.
The authors also thank the following research assistants for their diligent
work over the past several years: Daniel Asakawa, Catherine Drury, Moriah
LaChapell-Shalock, Benjamin Purkerson, Shannon Wineland. Gratitude is
expressed to the numerous landowners that granted property access.
6. Discussion
Merritt and Wohl (2006) provide an excellent summary of the
mechanisms by which plants are dispersed along river corridors. Seeds and
plant fragments may be transported by four fundamental mechanisms: (1)
anemochore (wind dispersion), (2) barochore (gravity dispersion), (3)
hydrochore (water dispersion), and (4) zoochore (animal transport, including
humans). The mechanism of dispersal is species dependent and a function
of numerous variables related to the life history traits of the plant in question.
The spatial distribution of adventive species in the Luckiamute watershed in
part reflect the life history characteristics and in part geomorphic and
anthropogenic processes occurring in the basin. As discussed by Merrit and
Wohl (2006), hydrochoric plants are typically limited in occurrence to within
several meters of the stream channel, while wind and animal dispersion
tend to disperse species more ubiquitously throughout the riparian zone and
along the riparian corridor.
9. SELECTED REFERENCES
Figure 10C. Plot of Japanese knotweed (Polygonum cuspidatum) cover along survey
traverses perpendicular to the active channel. Data are tallied from all 1-m2 quadrats
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