The Eastern Arc Mountains in Tanzania and the Atlantic Forest of Brazil are two of the most fragmented tropical biodiversity hotspots. Species-area relationships predict that their fragments will experience a substantial loss of species. Most of these extinctions will occur over an extended time, so reconnecting fragments could prevent species losses and allow locally extinct species to recolonize former habitats. An empirical relaxation time-area relationship for tropical bird communities estimates the time it takes to lose species. It also estimates the increase in species persistence by regenerating a forest connection one kilometer in width among the largest and closest fragments at eleven locations.
In Eastern Arc Mountains, regenerating 8,474 ha of forest would create >322,000 ha in total of restored contiguous forest. More importantly, it would increase the persistence time for species by a factor of 6.6 (range, 2.6 – 20.3) per location or ~2,293 years, on average, relative to individual fragments. In the Atlantic Forest, regenerating 6,452 ha of forest would create >251,000 ha in total of restored contiguous forest and enhance species persistence by a factor of 13.0 (range, 10.9 – 15.1) per location or ~5,102 years, on average, relative to individual fragments. Rapidly regenerating forest among fragments is important because mean time to first determined extinction across all fragments is 7 years. We estimate the cost of forest regeneration is $21 - $49 million dollars. It could provide one of the highest returns on investment for biodiversity conservation worldwide.