Assessing drought sensitivity across the shortgrass steppe biome
Date
2024
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Abstract
Net primary productivity (NPP) of grassland ecosystems is dependent on many biotic and abiotic factors. However, water availability is generally considered the primary determinant of NPP, as well as being key for defining grassland community structure, and thus it is imperative to understand how grasslands respond to drought in a climate where droughts are expected to become more frequent and severe. There is a well-documented negative relationship, described by the Huxman-Smith model, between drought sensitivity and mean annual precipitation (MAP) at spatial scales that span multiple biomes. In other words, drier ecosystems are usually more sensitive to drought than more mesic ecosystems. While this cross-biome pattern has been independently confirmed with a variety of research approaches, there is limited research that has explored how patterns of drought sensitivity vary with MAP within a single biome where the dominant species do not vary. My goal was to determine if this negative relationship is evident within a regionally extensive grassland biome generally dominated by a single grass species (Bouteloua gracilis or blue gramma). I characterized the spatial pattern and relationship between drought sensitivity and MAP across the shortgrass steppe biome of the North American Great Plains using satellite-derived Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) data (from 2000-2022) as proxies for vegetation productivity. Gridded annual precipitation data were obtained at a comparable spatial scale. I found a negative relationship between drought sensitivity and MAP within the shortgrass steppe biome, indicating that the Huxman-Smith model is also supported within a single biome. Thus, my results suggest that while changes in the dominant vegetation may contribute to the patterns observed between MAP and drought sensitivity at large spatial scales that include multiple biomes, gradients in MAP within a biome can also drive this negative relationship. As a result, directional changes in annual precipitation amounts have the potential to alter drought sensitivity directly, even if the dominant plant species do not change.