The scale dependency of spatial crop species diversity and its relation to temporal diversity

Abstract

Increasing crop species diversity can enhance agricultural sustainability, but the scale dependency of the processes that shape diversity and of the effects of diversity on agroecosystems is insufficiently understood. We used 30 m spatial resolution crop classification data for the conterminous United States to analyze spatial and temporal crop species diversity and their relationship. We found that the US average temporal (crop rotation) diversity is 2.1 effective number of species and that a crop’s average temporal diversity is lowest for common crops. Spatial diversity monotonically increases with the size of the unit of observation, and it is most strongly associated with temporal diversity when measured for areas of 100 to 400 ha, which is the typical US farm size. The association between diversity in space and time weakens as data are aggregated over larger areas because of the increasing diversity among farms, but at intermediate aggregation levels (counties) it is possible to estimate temporal diversity and farm-scale spatial diversity from aggregated spatial crop diversity data if the effect of beta diversity is considered. For larger areas, the diversity among farms is usually much greater than the diversity within them, and this needs to be considered when analyzing large-area crop diversity data. US agriculture is dominated by a few major annual crops (maize, soybean, wheat) that are mostly grown on fields with a very low temporal diversity. To increase crop species diversity, currently minor crops would have to increase in area at the expense of these major crops.

Crop genetic erosion: understanding and responding to loss of crop diversity

“…A particularly important methodological hurdle that, if overcome, would generate a deeper understanding of the implications of crop diversity change is the integration of temporal and spatial trends (Bonneuil et al ., 2012; Aramburu Merlos & Hijmans, 2020; Fenderson et al ., 2020). The research to date provides much more information on appearance/disappearance and numbers (richness) of varieties than it does on changes in their geographic extent.…”

Crop diversification in Idaho’s Magic Valley: the present and the imaginary

“…Based on prior analysis of national-level data (Burchfield et al 2019 ), Idaho’s Magic Valley is ranked as one of the most agro-diverse regions in terms of the number and types of crops grown in the US. Recent research corroborates these findings, identifying southcentral Idaho as a place with high temporal diversity (Aramburu Merlos and Hijmans 2020 ) and high spatial diversity with exceptionally high yields for major commodities (Nelson and Burchfield 2021 ; Burchfield and Nelson 2021 ). In addition to its diverse crop production, we selected this region for its strong commercial agribusiness; agribusiness contributes to over half of the region’s jobs and annual revenue (Hines et al 2018 ).…”

“…By using qualitative methods in this study to contextualize and interrogate the quantification of crop diversity from prior studies (Burchfield et al 2019 ; Aramburu Merlos and Hijmans 2020 ), we find that the implementation of certain crop diversification strategies within a landscape—and locating places and farmers currently engaged in strategies of diversified cropping—does not inherently promote or enact agroecological transformation. In the ways that agroecology cannot be reduced to a set of practices, the accumulation of crop diversification practices across a landscape may not inherently lead to pathways of sustainable change.…”

“…First, diversified farming lacks a clearly defined and accepted conceptual framework, and, thus, what differentiates it from non-diversified farming is often unclear (Hufnagel et al 2020 ). This has obfuscated discussions and implementation of diversification strategies, particularly the differences between temporal and spatial diversity (Aramburu Merlos and Hijmans 2020 ). Second, perceptions of agricultural biodiversity differ between researchers and farmers: researchers may hold idealistic views of the value of diversification, whereby farmers may not view those same processes positively (Maas et al 2021 ).…”

Product Diversification, Adaptive Management, and Climate Change: Farming and Family in the U.S. Corn Belt

“…Crop diversification is a critical definition whose implications for climate mitigation and adaptation are direct. Diversifying land covers can support biodiversity while potentially building soil and reducing pest pressures and farmers' chemical applications to their production systems (Bradshaw et al, 2004;Roesch-McNally et al, 2018;Merlos and Hijmans, 2020;Prokopy et al, 2020). Diversification via livestock and crop integration is another major approach to diversification (Garrett et al, 2017).…”