Submitted to: Frontiers in Environmental Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2020
Publication Date: 5/27/2020
Citation: Goslee, S.C. 2020. Drivers of agricultural diversity in the contiguous United States. Frontiers in Environmental Science. 4(75):1-12. https://doi.org/10.3389/fsufs.2020.00075.
Interpretive Summary: Agricultural diversity is related to ecosystem services such as habitat for wildlife and pollinators, soil health, nutrient cycling, and it improves food security. The USDA Cropland Data Layer was used to measure crop diversity for the contiguous United States, and to relate crop diversity to temperature and water availability for twenty agricultural regions. Irrigation was very important, although it and other variables such as soil texture and growing degree days varied in importance regionally. Agricultural diversity could be improved across most of the United States, but the greatest increases would come with irrigation. Given declining aquifers and changing climate, this is infeasible, and agricultural diversity may instead decline in the richest areas unless new agricultural systems can be developed.
Technical Abstract: The spatial heterogeneity of vegetation types on a landscape has been linked to multiple ecosystem functions, including habitat for wildlife and pollinators, water and nutrient cycling, and human aesthetic values. Although agricultural land uses are sometimes combined, diverse cropping systems are a valuable alternative to near-monocultural croplands. The USDA Cropland Data Layer was used to characterize crop diversity across the contiguous US for 2008-2018. Percentage of each crop type, along with non-crop uses such as forest and development, were calculated for each 4km PRISM climate data grid cell. To better understand the drivers of crop diversity, Random Forest modeling was used to assess the importance of climate, soils, and irrigation for patterns of crop effective richness for the contiguous United States, stratified by USDA Land Resource Region. The models explained 57-89% of the variation in maximum crop diversity, with irrigation being by far the most important explanatory variable in regions where it was employed. The drivers of change from 2008 to 2018 were less clear. Random Forest models explained only 20-60% of the change in agricultural diversity over the eleven-year period; both soil and climate properties were important, with no clear dominant drivers. Potential crop effective richness was greater than actual across the entire region studied, but substantial increases would require irrigation. Major changes in agricultural systems and infrastructure may be necessary to increase agricultural diversity at large spatial extents, and declining availability of water for irrigation could threaten the agricultural systems that are now most diverse.