Long-Term Site Potential Rangeland Fractional Component Cover and Deviation in Wyoming, USA

Monitoring rangelands by identifying the departure of contemporary conditions from long-term ecological potential allows for the disentanglement of natural biophysical gradients driving change from changes due to land uses and other disturbance types. We developed maps of ecological potential (EP) for shrub, sagebrush (Artemisia spp.), perennial herbaceous, litter, and bare ground fractional cover in Wyoming, USA. EP maps correspond to the potential natural vegetation cover expected by environmental conditions in the absence of anthropogenic and natural disturbance as represented by the best growing conditions and least disturbed period of the Landsat archive. EP was predicted using regression tree models with inputs of soil maps and spectral data associated with the 75th percentile of Normalized Difference Vegetation Index (NDVI) in the Landsat archive. We used contemporary (~2015) component cover maps on ecologically-intact sites with relatively low bare ground than expectations and with low amounts of annual herbaceous cover as training. We generated departure of vegetation cover by comparing the EP and contemporary (~2015) fractional cover. The departures represent land cover change from potential land cover and/or within state changes in 2015. Next, we converted EP and contemporary fractional cover maps into thematic land cover and evaluated departure to determine if it was great enough to result in land cover change. The contemporary conditions showed reduced shrub, sagebrush, litter, and perennial herbaceous cover and increased bare ground relative to EP. Known disturbances, such as energy development, fires, and vegetation treatments, are clearly visible on the departure maps, but not EP component maps. The most frequent departure from EP land cover was shrubland conversion to grassland. Land cover departures can be explained only in small part by known disturbance, such fire, and instead are ostensibly related to climate and land management practices. These drivers result in land cover departures that broadened the ecotone between shrubland and grassland relative to EP. Five EP layers are presented here; bare ground, perennial herbaceous, sagebrush, and shrub cover. Also available are two "crosswalked" (CW) land cover layers; 2015CW and EPCW. For more information see https://www.mrlc.gov/.