Using field data to validate remote sensing models of grassland phenology, biomass, and forage quality in the Upper Yellowstone River Basin
Concern that shifts in vegetation phenology patterns caused by climate change and human land use may impact ungulate migration and population dynamics highlights the need for landscape scale monitoring of vegetation phenology across the Greater Yellowstone Ecosystem (GYE). Phenology is directly related to vegetation biomass and forage quality, and is known to be a driver of ungulate migration patterns. Satellite-derived Normalized Difference Vegetation Index (NDVI) has gained attention as a tool for monitoring landscape scale vegetation phenology and biomass, but is limited by a lack of validation in varying land uses, elevations, and throughout the entire growing season. While widely used, NDVI is often limited in areas of high soil exposure, senescent vegetation, high biomass, and has only recently been linked to forage quality. In order to better understand the utility of NDVI, this study aims to validate the relationship between MODIS-derived NDVI and grassland phenology, biomass, and forage quality using field data from varying land uses, elevations, and periods of the growing season in elk summer migratory ranges the Upper Yellowstone River Basin of the GYE. Preliminary results suggest a strong relationship between NDVI and biomass, phenology, crude protein, digestibility and chlorophyll concentration in all land uses and elevations at the beginning of the growing season. Validated results will provide managers with information on the utility of NDVI as a proxy for phenology, biomass, and forage quality critical for monitoring the effects of climate and land use change on vegetation dynamics important for ungulate populations in the GYE.