Canopy transpiration is a major factor determining crop evapotranspiration and energy budgets. Unfortunately the development of robust models of canopy transpiration is hindered by a lack of reliable data due to the difficulties of making canopy-scale measurements. However, measurements of canopy water vapor and carbon fluxes via gas exchange techniques are possible in controlled environments. Simultaneous measurements of transpiration, photosynthesis, and canopy temperature were made in wheat and soybean communities. These data were used to calculate chamber aerodynamic and canopy stomata! conductances, and to model the response of canopy transpiration to CO2concentration and vapor pressure deficit. Canopy stomata! conductance was found to decrease diurnally by 20-30% in well-watered crops grown under constant environmental conditions. The magnitude of this diurnal decrease in the canopy stomata! conductance of wheat and soybean decreased with increasing ambient CO2 concentrations. Eight models describing how canopy stomatal conductance responds to environmental changes were incorporated into a canopy transpiration model. The results and methods developed in this study will allow future physiologically-based canopy transpiration models to incorporate these models for predicting the response of transpiration rates in controlled environments.

No description available.

Arches National Park, located in southeastern Utah, lies in a transition zone between the southwestern hot desert and the western cold desert, but it is floristically most similar to the hot desert. The major plant communities are as follows: Juniper-pinyon, blackbrush, grasslands and sand dune association. Other community types occur but occupy very limited areas. All of the communities studied have a high degree of uniqueness and merit recognition as separate entities. Blackbrush showed the greatest overall similarity to other communities and was most similar to the sand dune communities. The hanging gardens were the most distinctive and covered the smallest area of the communities present in the Park. Cluster analysis placed blackbrush, sand dunes and juniper-pinyon on the xeric end of a moisture gradient and streamsides and hanging gardens on the mesic end.

A study area on the southern extensions of the Great Basin cold desert (Kaiparowits Basin, Utah) was selected which has had varying amounts of disturbance. Areas with similar slope and exposure in the Shadscale community were sampled. At each site, soil samples were collected and percent sand, percent clay, percent silt, soluble salts, and hydrogen ion concentrations were measured. Cluster analysis based on percent frequency of the perennial species showed that eight groups or sub-communities were definable within the area sampled. Patterns within the vegetation were shown to be independent with the use of cluster analysis. Discriminant analysis on soil factor patterns associated with the groups were shown to be non-correlated with the vegetation patterns. Gradient analyses were therefore conducted with edaphic factors in relationship to the 11 most prominent perennial species. Distinct trends were shown to exist for nine of the 11 species. Evaluation of grazing on the 14 most-prevalent species indicate that grazing affects all species studied, under moderate to heavy stocking rates.

No description available.

Thesis (Ph. D.)--University of British Columbia, 1997. / Includes bibliographical references (leaves 127-133).

An examination of the effectiveness of seeding, burning, and mowing in the reestablishment of tallgrass prairie species on overgrazed and abandoned pastureland. The study site is a 20 acre tract on U.S. Corps of Engineers land below Lake Lewisville in Denton County, Texas. The site was partitioned into thirty-nine 40 by 40 meter plots with seeding (carried out in 1996) and management treatment (burning, mowing, and no maintenance carried out in 1998) randomly applied following a two level design. For each plot, nine stratified-random 0.1 m2 subplots were examined and shoot counts for each species recorded. The effects of the treatments on individual species and species richness were analyzed with a two-way ANOVA followed by a SNK multiple range test, both on ranked data. Community level analysis was conducted with both a MANOVA on ranked data and a Canonical Correspondence Analysis on raw data. Results indicate that seeding positively affected species richness, particularly when combined with either burning or mowing in the early spring. Mowing also significantly increased species richness in areas that were not seeded, while burning negatively affected species richness on unseeded plots. Treatments significantly affected community composition with treatments having the most clear effect on spring and summer forbs.

Non-forested ecosystems dominate high elevation sites in coastal British Columbia, yet there has never been a comprehensive classification or mapping of all high-elevation community types. The objective of this study is to collate and expand upon previous classifications, and thereby to increase our understanding of the habitats and composition of these plant communities.

This report expands and clarifies previous classifications of non-forested plant communities from upper subalpine and alpine locations in coastal British Columbia. A total of 80 plots (releves) sampled specifically for this study were added to 202 releves from published and unpublished studies conducted since 1963. We used tabular and multivariate methods to synthesize and classify plant communities according to the Braun-Blanquet approach. Plant communities were classified into 37 vegetation units (associations or subassociations) which served as the basis of the resulting hierarchical classification. We describe the habitat and species composition of these vegetation units and their relationship to units recogized elsewhere in the Pacific Northwest. We then present eight generalized habitat types which we propose as the basic units for future ecosystem mapping. Each of these habitat types includes a predictable mosaic of vegetation units whose pattern occurs at too fine a scale to map individually.

Thesis (M.S.)--North Carolina State University, 2004. / Title from PDF title page (viewed on Apr. 3, 2005). Includes vita. Includes bibliographical references.