Divergent trajectories of crop simplification and diversification in the United States, 1840–2022

Long-term agricultural change in the United States is often described as a uniform process of crop simplification driven by modernization and specialization. However, the long-term regional pathways through which crop diversity has simplified or diversified remain poorly understood. We analyze county-level crop composition data from the U.S. Agricultural Census spanning 1840–2022 to examine long-term spatiotemporal changes in crop diversity. Given the multiple dimensions of crop diversity, we characterize crop diversity using compositional complexity, crop variety, and crop area evenness. These dimensions are examined using temporal breakpoint detection, spatial autocorrelation analysis, and unsupervised trajectory classification methods. National trends do not indicate consistent simplification across the three diversity dimensions but reveal a mid-twentieth century shift toward agricultural systems with fewer major crops and more even crop area shares. By contrast, at the county-level, crop diversity trajectories did not converge toward a single outcome. Instead, eight distinct integrated trajectory classes were identified: simplification pathways accounted for 63.72% of counties, while diversification pathways accounted for 36.28%. These pathways exhibit strong spatial structure, few intermediate outcomes, and long-lasting regional differentiation, suggesting path-dependent crop diversity dynamics shaped by historical specialization and spatial context. Our findings show that changes in U.S. crop diversity are temporally discontinuous, spatially divergent, and structurally complex. The integrated trajectory framework helps identify regional simplification and diversification pathways within agricultural land-use systems and provides a screening tool for regionally differentiated crop diversification policy.