Limits to agricultural land for retaining acceptable levels of local biodiversity

Several studies have proposed maximum allowable areas of cropland (12.6–15.18% of terrestrial area) as environmental sustainability requirements, yet none have so far considered the minimum biodiversity levels required to support ecosystem functioning at acceptable levels. Here, we use a decision tree-based optimization model to estimate the maximum area of cropland and pasture that would meet—or come closest to meeting—the acceptable levels of local biodiversity proposed in the literature (90% local species abundance and 80% local species richness compared with an undisturbed baseline). We model four scenarios under which we vary two key sources of uncertainty: the maximization function and the potential of secondary vegetation to maintain biodiversity. The model finds that a maximum of 4.62–11.17% of the global ice-free land can be allocated to cropland (and 7.86–15.67% to pasture) to meet these biodiversity constraints—a lower level than was suggested in previous studies. The results are very sensitive to the minimum acceptable biodiversity values and the biodiversity response factors used, but the size of the disparity between current cropland area and our results suggests that actions to limit or reduce the area dedicated to agriculture should feature more prominently in policy discussions.