Restoring tropical diversity: beating the time tax on species loss

Background

Remnant tropical forests are being deforested at approximately the same rates as cleared lands revert to secondary forest, leading to a fragmented or patchwork landscape. Small patches of remnant forest may remain, but these inevitably lose species to local extinction. Despite forestation rates that may appear relatively stable on paper, vegetation matrices are rapidly changing from a diversity of old-growth species to a much smaller number of early-successional and non-native species that dominate natural-regeneration and reforestation sites.

Research goals & methods

This review article discusses the concept of a ‘time tax’ delaying recruitment of diverse species on cleared sites. While other authors have discussed the time delay in recruitment caused by soil degradation (Lugo 1988), this paper focuses on the ‘time tax’ of a pioneer vegetation matrix, causing local or extensive loss of deep-forest species. Deep-forest species are often unable to recruit into a pioneer matrix due to distant seed sources or incompatible structure. However, some deep-forest species can establish in cleared land with survival rates >70%. Bypassing early domination of pioneer trees in regenerating matrices, or enriching matrices with animal-dispersed forest trees, may stem the loss of species from forest fragments and accelerate succession far from the edges of old forest.

Conclusions & takeaways

Planting disperser-limited trees that establish in open ground may bypass 30–70 years of species attrition in isolated remnants by attracting animals that encourage normal processes of seed dispersal into and out of the fragments. Development of criteria for selection of persistent, reasonably rapidly growing, animal-dispersed species that are mixed with planted or naturally arriving pioneers will be an important component of enrichment planting.