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Plant communities of the grassy balds of Marys Peak, OregonSnow, Billy Douglas 26 April 1984 (has links)
Graduation date: 1984
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Analysis and prediction of patterns in lichen communities over the western Oregon landscapePeterson, Eric B. 24 May 2000 (has links)
The diverse lichen flora of the Pacific Northwest is being impacted by
population growth and by forest management practices. Accumulating information
about our lichen flora will improve our conservation strategies. This dissertation first
collects information to improve our understanding of how lichen communities vary
among forests of differing structure, and across the western Oregon landscape. It then
proposes a method to predict species occurrence in unsampled sites by utilizing the
information on forest characters and environmental gradients at sampled sites.
Macrolichen communities sampled in coniferous forests revealed that old-growth
stands (>200 yrs old) harbored communities that differed from those in young
forests (50-110 yrs old). Even more atypical communities occurred in macrolichen
hotspots, which were primarily in riparian zones. Many macrolichen species were
associated with these hotspots, including numerous nitrogen-fixing cyanolichens.
Macrolichen species associated with old-growth forested plots included the nitrogen-fixing
lichen Lobaria oregana and several forage-providing alectorioid lichens. The
presence of remnant old trees apparently increased the occurrence of old-growth
associates in young stands. The calicioids, a group of microlichens investigated only in
the Cascades, had a strong association with old growth forest and remnant trees.
Diversity of calicioids may also be increased by legacy structures such as old snags and
wolf trees. These structures increase continuity between current and previous stands.
Macrolichen communities varied between the Coast and Cascade Mountain
Ranges, following climatic gradients, particularly annual precipitation. Successional
patterns in macrolichen communities appeared to differ between the mountain ranges.
The modeling method proposed for using habitat associations to predict
occurrence has several advantages over common modeling methods, such as regression.
The method is simple, avoids parametric assumptions, provides easy updating of
models as additional sites are sampled, and automatically accounts for interactions
among predictor variables. It can be linked with GIS data and software to map
estimated probability of occurrence across landscapes. The data on calicioids from the
Cascades, supplemented with additional stand inventories, were used to test and
demonstrate the modeling method. / Graduation date: 2001
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Community analysis of the Wyoming big sagebrush alliance and functional role of Wyoming big sagebrushDavies, Kirk W. 19 September 2005 (has links)
This study consisted of two research projects in the Wyoming big sagebrush
(Artemisia tridentata ssp. wyomingensis (Beetle & A. Young) S.L. Welsh) alliance,
the most extensive of the big sagebrush complex in the Intermountain West. In the
first project, we intensively sampled 107 relatively undisturbed, late seral Wyoming
big sagebrush sites across the High Desert, Humboldt, and western Snake River
Ecological Provinces to investigate vegetation heterogeneity and the relationship of
environmental factors with vegetation characteristics. Vegetation characteristics were
highly variable across the region. Perennial grass and total herbaceous cover varied
more than six and sevenfold, respectively between minimum and maximum values.
Sagebrush cover averaged 12%, but ranged between 3 and 25%. With the exception
of perennial grass cover (p<0.0001, r²=0.52), limited variability in other vegetation
characteristics was explained by environmental variables.
In the second project, we investigated the functional role of Wyoming big
sagebrush by using undisturbed and sagebrush removed (with burning) treatments and
comparing vegetation and microsite characteristics under (subcanopy) to between
sagebrush canopy (interspace) zones. Wyoming big sagebrush influenced associated
vegetation and microsites. On sites receiving high incidental radiation, perennial grass
and total herbaceous cover and density were greater in the subcanopy than interspace
zones (p<0.05). On north aspects, these differences were not as pronounced
suggesting sagebrush's influence on associated vegetation is site dependent.
Temperature extremes were mediated and soil water content was greater in the
subcanopy than interspace zones during the growing season. Results indicated that the
subcanopy zone can be a more favorable environment to herbaceous vegetation than
the interspace zone. Wyoming big sagebrush is important to community resource
capture and use. Plots with sagebrush had greater soil water content at the start of the
growing season and produced more total biomass compared to where sagebrush had
been removed in both post-fire years (p<0.05). However, higher Thurber's
needlegrass photosynthetic rates and greater herbaceous cover and production where
sagebrush had been removed suggested that more resources were available to
herbaceous vegetation in the absence of sagebrush. / Graduation date: 2006
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Environmental Gradients, Community Boundaries, and Disturbance the Darlingtonia Fens of Southwestern OregonTolman, Deborah A. 01 January 2004 (has links)
The Darlingtonia fens, found on serpentine soils in southern Oregon, are distinct communities that frequently undergo dramatic changes in size and shape in response to a wide array of environmental factors. Since few systems demonstrate a balance among high water tables, shallow soils, the presence of heavy metals, and limited nutrients, conservative efforts have been made to preserve them. This dissertation investigates the role of fire on nutrient cycling and succession in three separate fens, each a different time since fire. I specifically analyze the spatial distributions of soil properties, the physical and ecological characteristics of ecotones between Jeffrey pine savanna and Darlingtonia fens, and the vegetation structure of fire-disturbed systems. Soil, water, and vegetation sampling were conducted along an array of transects, oriented perpendicular to community boundaries and main environmental gradients, at each of the three fens. Abrupt changes in vegetation, across communities, were consistently identified at each of the three sites, although statistical analysis did not always identify distinct mid-canopy communities. Below-ground variables were likewise distinguished at the fen and savanna boundary for two of the three sites. At the third site, discontinuities did not align with the fen boundaries, but followed fluctuations in soil NH4. My results suggest that below-ground discontinuities may be more important than fire at preserving these uniquely-adapted systems, while vegetation undergoes postfire succession from fen to mid-canopy to savanna after approximately 100 years since fire. Although restoration of ecosystem structure and processes was not the primary focus of this study, my data suggest that time since fire may drive ecosystem processes in a trajectory away from the normal succession cycle. Moreover, time since fire may decrease overall vigor of Darlingtonia populations.
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