Remote sensing and ecosystem simulation modeling of the intermountain sagebrush-steppe, with implications for global climate change.

摘要

Three papers are presented that focus on remote sensing and ecosystem simulation modeling of the Intermountain Northwest sagebrush-steppe ecosystem. The first utilizes Advanced Very High Resolution Radiometer data to derive seasonal greenness indices of three predominant vegetation communities in south-central Washington, U.S.A. Temporal signatures were statistically separated, and used to create a supervised classification for the three communities by integrating Normalized Difference Vegetation Indices over the growing season. The integrated classification scheme accuracy was 75% when compared to 53 ground-truthed sites, but was less accurate (62%) when applied to a more topographically variable region.; The second paper develops a logic for treating the intermountain sagebrush-steppe as a mosaic of distinct, hydrologically partitioned vegetation communities, and identifies some critical ecophysiological considerations for process modeling of arid ecosystems. Soil water and nutrient dynamics of an ecosystem process model were modified to simulate productivity and seasonal water use patterns in Artemisia, Agropyron, and Bromus communities for the same south-central Washington study site. 60 year simulations maintained steady state vegetation productivity while predicting soil moisture content for 56 dates in 1992 with R{dollar}sp2{dollar} values ranging from 0.93 to 0.98.; In the third paper, the model was used to derive projections of the response of the ecosystem to natural and general circulation model (GCM)-predicted climate variability. Simulations predicted the adaptability of a less productive, invasive grass community (Bromus) to climate change, while a native sagebrush (Artemisia) community does not survive the increased temperatures of the GCM climates. High humidity deficits and greater maintenance respiration costs associated with increased temperatures limit the ability of the sagebrush community to support a relatively high biomass, and substantial increases in soil water storage and subsurface outflow occur as the vegetation senesces.