The effect of the type and speed of dominant land-cover transitions on patterns of tropical forest fragmentation

Abstract Context The speed and severity of tropical forest conversions to croplands and rangelands, give rise to distinct fragmentation patterns, altering species composition and ecosystem resilience. While the type of the surrounding land-cover can mitigate these impacts through landscape complementation, the role of specific land-cover transitions and their speeds in shaping forest fragmentation patterns remains poorly understood at the pan-tropical scale. Objectives We study how fragmentation dynamics vary by the type, speed and severity of the land-cover transition, while also accounting for the constraints imposed by the initial forest amount. We hypothesize that forest fragmentation patterns will vary by transition type, with rapid transitions producing compact forest patches with distinct geometric boundaries. Methods We analyzed fragmentation dynamics across 87,510 tropical forest landscapes of size 30.09 km 2 using global land-cover maps from 1992–2020. Results Our results show that: (1) grasslands exhibit a patchy and dispersed pattern of expansion, while croplands and shrublands exhibit threshold behavior—triggering rapid fragmentation once initial forest cover falls below 60%; (2) slower rates of cropland expansion contribute to increased fragmentation of tropical forests, while rapid rates of cropland expansion were associated with compact and aggregated forest fragments; and (3) intermediate transition speeds (12–15 years) minimize fragmentation for grassland transitions, and lead to increased aggregation in the case of shrublands. Conclusion These results highlight how patterns of forest fragmentation vary according to the type and speed of land-cover transitions, advancing our understanding of the underlying drivers of distinct fragmentation pathways in tropical forests.