The breakdown of ecosystem functionality driven by deforestation in a global biodiversity hotspot

The pace of deforestation in tropical forests has achieved unprecedented rates, requiring effective and achievable conservation mitigations that are also easily understood by society and policy makers. In this context, we report the outcomes from a large-scale project located in the threatened Atlantic Forest (SISBIOTA network) to understand how deforestation affects ecological patterns and processes in human-modified landscapes. In particular, we compiled data from 28 studies that evaluated habitat quality, biodiversity maintenance or ecological processes and scrutinised their responses along the gradient of forest loss. After a decade of research effort, we provide evidence of key changes in forest quality, species diversity and ecological processes that are ultimately affecting forest functioning of the remaining patches. As deforestation progresses, we unveiled a clear retraction of local vegetation structure, in which forests become similar to secondary forests, as are characterised by retaining shorter and thinner trees, higher foliage density and increased canopy openness. Besides being hotter, patches embedded within deforested landscapes present reduced quality, evidenced by low fruit production and quality. Such changes cascade to disruptions in biodiversity maintenance and ecological processes. Specifically, forest-specialist species exhibit reduced diversity (e.g., juvenile and adult trees, birds and mammals) and for some groups, are compensated by the increase in habitat-generalist species. Furthermore, forest patches immersed in deforested landscapes experience strong alterations in nutrient cycling and carbon stocks, increase of leaf herbivory, reduction of frugivory, and finally, a simplification in bird-plant interactions. Preventing deforestation is imperative, but restoration and rewilding are also required to safeguard forest-dweller species and, consequently, enable ecological functionality.