Spatial and temporal scale effects on assessment of a regional ecosystem model: Modeling climate change in Glacier National Park, United States of America.

摘要

A regional ecosystem model (RHESSys) was tested in the Lake McDonald and St. Mary's Lake watersheds of Glacier National Park, with the hypothesis that predictions of the ecosystem simulation are scale dependent. Carbon budgets were found less sensitive than water budget predictions as a consequence of models used to predict soil water distribution. Temporal and spatial simplifications of the ecosystem model predicted comparable spatial patterns and average carbon assimilation among different scale simulations.; Leaf area index (LAI) is an important input parameter for RHESSys which defines the amount of carbon and nitrogen present within the ecosystem and constrains the absorption of radiant energy and cycling of water. I tested the ability of Landsat Thematic Mapper data for estimating LAI using sampled field LAI values for calibration. This process included refining field-LAI sampling methodologies due to biases in optically-based LAI detection devices. I found that LAI-satellite reflectance values were not directly comparable because of incompatibility between the timing and spatial representation of either observations. Satellite LAI values were estimated by aggregating data for large hillslopes, indicating that fine scale satellite data represent the general trend in LAI but not at its native resolution.; The validity of ecosystem simulations were tested using field data collected on carbon and water budgets. Predicted soil carbon flux, aboveground production, net primary production (NPP), snowpack, hydrologic discharge, soil water content, and leaf water potentials were correlated with observed values. Correlation improved with spatial and temporal aggregations.; Ecosystem simulations demonstrated that NPP is correlated with biogeographical distribution of lifeforms across the Continental Divide. Long-term variation in NPP is indicative of lifeform type and is used to infer community stability given linkages to physiological stress and disturbance potentials. Simulated variable climate showed upper treelines changing with greater encroachment by broad-leafed shrub communities, while lower coniferous forest treelines showed greater instability and greater production in broad-leafed communities. Water and nitrogen limits on aboveground production changed with variable climate indicating changes in site nutrient and water limitations. These limits were lifeform specific which influence competition and landcover change.