PARENT SESSION
Oral Session # 70: Landscape Ecology.
Presiding: S Hannon
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 201.

Controls over large-scale ecosystem processes: The role of land use.

Bradford, John^{*,1, 2}, Lauenroth, William^{1, 2, 3}, Burke, Ingrid ^{1, 2, 3}, Paruelo, Jose⁴, ¹ Graduate Degree Program in Ecology, Fort Collins, CO, USA² Department of Forest, Rangeland and Watershed Stewardship, Fort Collins, CO, USA³ Natural Resource Ecology Laboratory, Fort Collins, CO, USA⁴ Facultad de Agronomía, Buenos Aires, B.S.A.S., ARGENTINA

ABSTRACT- Identifying the conditions and mechanisms that control ecosystem processes is a central goal of ecosystem ecology. Ideas have ranged from single limiting-resource theories to colimitation by nutrients and climate, to simulation models with edaphic, climatic and competitive controls. Although some studies have begun to consider the influence of land use practices, especially cultivation, few studies have quantified the impact of cultivation at large scales relative to other known controls over ecosystem processes. We utilized a 9-year record of productivity, phenology, climate, weather, soil conditions and cultivation in the U.S. Great Plains to quantify the controls over spatial and temporal vegetation patterns and estimate the process sensitivity to specific driving variables. We considered climate, soil conditions and long-term average cultivation as spatial controls and weather and interannual cultivation variations as temporal controls. We found that, within this region, productivity variation is primarily spatial, whereas phenology variation is more evenly split between spatial and temporal components. Our models explained more of the variation in productivity than phenology and more of the spatial than the temporal patterns. Our results indicate that although climate is the most important spatial variable, cultivation explains a substantial fraction of the residual variability. Soil conditions contributed very little to our spatial models. Weather and cultivation deviation both made modest contributions to the temporal models. These results suggest that the controls over phenology and temporal processes are not well understood. Our sensitivity analysis indicates that productivity is more sensitive to climate than weather and is very sensitive to cultivation intensity. In addition to identifying potential knowledge gaps, these results provide insight into the probable long- and short-term ecosystem response to changes in climate, weather, and cultivation.

Key words: phenology, productivity, landuse