Drivers and ecological impacts of deforestation and forest degradation in the Amazon

Abstract

Deforestation (the complete removal of an area’s forest cover) and forest degradation (the significant loss of forest structure, functions, and processes) are the result of the interaction between various direct drivers, often operating together. By 2018, the Amazon forest had lost approximately 870,000 km2 of its original cover, mainly due to expansion of agriculture and ranching. Other direct drivers of forest loss include the opening of new roads, construction of hydroelectric dams, exploitation of minerals and oil, and urbanization. Impacts of deforestation range from local to global, including local changes in landscape configuration, climate, and biodiversity, regional impacts on hydrological cycles, and global increase of greenhouse gas emissions. Of the remaining Amazonian forests, 17% are degraded, corresponding to 1,036,080 km2. Forest degradation has various anthropogenic drivers, including understory fires, edge effects, selective logging, hunting, and climate change. Degraded forests have significantly different structure, microclimate, and biodiversity as compared to undisturbed ones. These forests tend to have higher tree mortality, lower carbon stocks, more canopy gaps, higher temperatures, lower humidity, higher wind exposure, and exhibit compositional and functional shifts in both fauna and flora. Degraded forests can come to resemble their undisturbed counterparts, but this depends on the type, duration, intensity, and frequency of the disturbance event. In some cases this may impede the return to a historic baseline. Avoiding further loss and degradation of Amazonian forests is crucial to ensuring that they continue to provide valuable and life-supporting ecosystem services.