Land use and climate change modifies the spatio-temporal pattern of forage availability in the Greater Yellowstone Ecosystem

Background/Question/Methods  Evidence increasingly suggests that climate change is altering landscape scale vegetation phenology as depicted by satellite sensors (land surface phenology). We hypothesize that climate and land use changes interact to substantially affect the land surface phenology of grasslands in the Northern Rockies. Specifically, we predict shorter growing seasons and lower peak rates of photosynthetic activity at high elevations, while lower elevations are experiencing longer growing seasons and higher peak productivity as a result of human land use. This study takes place in the Yellowstone and Gallatin drainages of the northern portion of the Greater Yellowstone Ecosystem (GYE). This region is characterized by an intense seasonality of long harsh winters and short summers. It is also home to some of the best ungulate habitat in North America including the Northern Range within Yellowstone National Park’s (YNP) boundaries. However, the protected habitat available to ungulates in YNP is not always sufficient to sustain these animals year-round and they are sometimes forced onto neighboring private lands to meet energy and other requirements. This study uses MODIS derived 250-meter normalized difference vegetation index (NDVI) as a measure of photosynthetic activity and statistical models to explore the relationship between biophysical, climate and land use variables and NDVI time-series. Results/Conclusions Results show that NDVI on unmanaged high elevation grasslands demonstrate a typical uni-model annual pattern of productivity and remain tightly coupled to the variability of climate events. It remains unclear however, whether the length of growing season demonstrates a clear decreasing trend. This is in contrast to lower elevation private lands where there is significant variation between land uses and individual land use sites; some of which are not as tightly coupled to climate events as a result of human land use. Length of growing season at lower elevation sites does appear to show an increasing trend. The relationship between patterns of forage productivity and ungulates in the GYE remains poorly understood. However, this project presents evidence that climate and land use change have the ability to significantly alter future patterns of grassland productivity in the Northern Rockies.