Amazonian secondary forests are greatly reducing fragmentation and edge exposure in old-growth forests

Restoration of tropical landscapes through the expansion of secondary forests is crucial for climate change mitigation and offers co-benefits for biodiversity. However, the strength of these benefits is influenced by the position of these secondary forests within the landscape. Recovery of both carbon stocks and biodiversity in secondary forests are enhanced by proximity to old-growth forests, and old-growth forests may benefit from secondary forests in return through buffering of edge effects and reduced fragmentation. However, to date there has been no biome-wide assessment of secondary forest location relative to old-growth forests. We mapped Amazonian secondary forests and explored their proximity to old-growth forests of different conditions. We then calculated the extent to which secondary forests buffer old-growth edge forest (<120 m from an edge) and the influence of secondary forests on fragmentation. In 2020, 41.2% of Amazonian secondary forest was directly adjacent to old-growth forest and 94.1% was within a fragment connected to old growth. However, adjacency and connectedness fell to 20.1% and 57.4% respectively when only considering extensive structurally intact old-growth forest. Secondary forests buffered 41.1% of old-growth edge forest and, when acting as corridors, reduced the total number of old-growth fragments by 2 million. Our results reveal the importance of understanding spatial context when examining the potential benefits of increasing secondary forest cover. Improved understanding of the benefits of locating secondary forests next to old-growth forests could support the development of more effective climate change mitigation and restoration strategies.