Habitat fragmentation can either increase or decrease with habitat loss

Context: A key aspect of the fragmentation debate in conservation biology is whether fragmentation effects on biodiversity should capture the combined or separate effects of habitat loss and fragmentation, i.e., breaking apart of habitat into multiple patches. A common argument for treating loss and fragmentation as a single phenomenon is that human-caused habitat loss almost always leads to fragmentation. Objectives: Here we assessed whether forest loss consistently results in fragmentation, at a global extent and across spatial scales commonly considered in landscape ecology. Methods: We evaluated how often forest loss resulted in a decrease versus increase in fragmentation for 150,000 randomly-selected forest locations. We delineated landscapes of six sizes (radii of 0.25 to 10 km) at each location. For the subset of landscapes that lost forest between 2000 and 2020, we estimated the change in fragmentation using four different measures of fragmentation. Results: A decrease in forest fragmentation was a common outcome of forest loss. Across four measures of fragmentation, six landscape sizes, and all forested biomes, we found forests were more fragmented after forest loss 51% of the time and less fragmented 44% of the time. Conclusions: Our results show that the fact that fragmentation often results from habitat loss does not mean that fragmentation is the inevitable consequence of habitat loss. Effects of habitat loss on biodiversity often differ from those of fragmentation separate from habitat amount (fragmentation per se). Thus, understanding the effects of fragmentation per se on biodiversity is not only feasible, it is fundamental for developing effective habitat conservation plans to address biodiversity loss.