Two studies on Catherine Creek and Meadow Creek of the Upper Grande Ronde
River basin, quantified several physical and biotic influences on woody riparian community
composition and structure. The Catherine Creek study examined the association of woody
riparian species with elevational and geomorphic gradients. The Meadow Creek study
examined the influence of mammal herbivory on composition and abundance of woody
riparian species.
At Catherine Creek, twenty nine plots were established at 50 m intervals of
elevation from near the stream origin at 2207 m in the Wallowa Mountains to the foothills
of the Grande Ronde Valley at 988 m. Woody plant community composition was
associated with the dominant environmental variable, elevation. Distribution of dominant
riparian species was strongly associated with fluvial surfaces. Black cottonwood (Populus
balsamifera) was associated with gravel and cobble bars proximal to the stream channel,
and along with ponderosa pine (Pinus ponderosa) was also associated with elevated
boulder bars. Alders (A. incana and A. viridis) and willows (Salix bebbiana, S. boothii, S.
exigua, S. lucida, S. melanopsis, S. prolixa, and S. sitchensis) were associated with annual
floodplains.
At Meadow Creek, grazing by cattle was ended in 1991 on the entire study reach
and three deer and elk exclosures were built within the reach adjacent to the creek. Inside
deer/elk exclosures from 1991 to 1995, mean heights of tagged cottonwoods, willows,
and alders increased by 86% to 180%. Outside exclosures, mean heights of cottonwoods
and alders increased 109% and 99% respectively, but willows showed little change in
height. Both inside and outside of exclosures mean crown volume of cottonwoods
increased over 1000% and mean crown volume of alders increased over 600%. Willow
volume inside exclosures increased 376% in root sprouting (clonal) species and 528% in
crown sprouting (non-clonal) species, while outside of exclosures volume increased 79%
and 144% respectively. On both sides of exclosure fences, beaver herbivory had a
significant effect on cottonwood height growth in 1994 and 1995, and on height and
crown volume growth of willows in 1995. Over 50% of stem density increase on
transects was attributable to expansion within two large clones of Salix melanopsis inside
exclosures. Excluding these two clones, overall woody plant density increased by 72%
from 3.7 plants per 100 m�� of transect in 1991 to 6.3 plants per 100 m�� of transect in
1995. / Graduation date: 1999
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33630 |
| Date | 10 June 1998 |
| Creators | Lytjen, Danna J. |
| Contributors | Kauffman, J. Boone |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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