Tropical forest in Brazil

Tropical forest in Brazil. Photo: Alexander Lees

A large and expanding part of today’s tropical forest cover consists of secondary forests that have regenerated on previously deforested land. These secondary forests play a pivotal role in the carbon cycle and as potential habitat for forest biota. Nevertheless, their capacity to regain the biotic attributes of undisturbed primary forests remains poorly understood.

This article gives a comprehensive assessment of secondary forest recovery, using extensive tropical biodiversity, biomass, and environmental data sets. These data, collected in 59 naturally regenerating secondary forests and 30 adjacent primary forests in the eastern Amazon, cover more than 1600 species of large‐ and small‐stemmed plants, birds and dung beetles, and a variety of forest structure, landscape context and topoedaphic predictors.

After up to 40 years of regeneration, the secondary forests showed a high degree of biodiversity resilience, with different taxa recovering on average 88% of the mean species richness and 85% of mean species composition found in the undisturbed primary forests. During the first 20 years of succession, the period for which the authors had accurate age data, biomass on in secondary forests recovered at 1.2% per year, equivalent to a carbon uptake rate of 2.25 Mg/ha per year, while species richness recovered at 2.6% and composition at 2.3% per year on average. For all taxonomic groups, biomass was strongly associated with species distributions in secondary forest. However, other variables describing habitat complexity – canopy cover and stem density in the forest understorey – were equally important occurrence predictors for most taxa. Species responses to biomass revealed a successional transition at approximately 75 Mg/ha, marking the influx of forest species of high conservation value.

Overall, the results show that naturally regenerating secondary forests can accumulate substantial amounts of carbon and support many forest species. However, the surveyed secondary forests did not to return to a typical undisturbed primary forest state, underlining that secondary forests are not a substitute for undisturbed primary forests.