The future of tropical forest species

Deforestation and habitat loss are widely expected to precipitate an extinction crisis among tropical forest species. Humans cause deforestation, and humans living in rural settings have the greatest impact on extant forest area in the tropics. Current human demographic trends, including slowing population growth and intense urbanization, give reason to hope that deforestation will slow, natural forest regeneration through secondary succession will accelerate, and the widely anticipated mass extinction of tropical forest species will be avoided. Here, we show that the proportion of potential forest cover remaining is closely correlated with human population density among countries, in both the tropics and the temperate zone. We use United Nations population projections and continent-specific relationships between both total and rural population density and forest remaining today to project future tropical forest cover. Our projections suggest that deforestation rates will decrease as population growth slows, and that a much larger area will continue to be forested than previous studies suggest. Tropical forests retracted to smaller areas during repeated Pleistocene glacial events in Africa and more recently in selected areas that supported large prehistoric human populations. Despite many caveats, these projections and observations provide hope that many tropical forest species will be able to survive the current wave of deforestation and human population growth. A strategy to preserve tropical biodiversity might include policies to improve conditions in tropical urban settings to hasten urbanization and preemptive conservation efforts in countries with large areas of extant forest and large projected rates of future human population growth. We hope that this first attempt inspires others to produce better models of future tropical forest cover and associated policy recommendations.