- Tropical forests can regrow within decades, with species abundance and diversity recovering quickly, but full ecological recovery—especially the return of original species composition—takes much longer.
- Many mobile species such as birds, bats, and bees persist or return early, helping drive regeneration by dispersing seeds and pollinating plants, while slower-moving or long-lived species lag behind.
- Forests may regain high numbers of species relatively fast, but the specific mix of old-growth species takes decades or longer to reassemble, meaning a regrown forest is not the same as the one that was lost.
- Recovery depends on time, prior land use, and proximity to intact habitat, suggesting that protecting and allowing secondary forests to regenerate can be a practical and cost-effective path for restoring biodiversity.
A tropical forest can regrow quickly. What is harder to see is how long full ecological recovery takes. A pasture left to regenerate may, within a few decades, resemble a forest again. But resemblance can be misleading. Beneath the canopy, recovery proceeds at different rates across species, shaped by how species persist through disturbance and return afterward.
A recent study of a lowland rainforest in Ecuador offers a detailed account of this process across a wide range of organisms. Drawing on data from 62 plots spanning active agriculture, secondary forest, and old-growth stands, the researchers examined how biodiversity recovers following land use. Their analysis extends beyond trees to animals and microbes, treating forests as systems of interaction rather than collections of species.
The findings, published this week in Nature, point to a mixed picture. Secondary forests—those regrowing after clearance—now account for roughly 70% of tropical forest area. Their role in conservation has often been overlooked. The study finds that these landscapes can regain much of their biological richness within a few decades, provided they are allowed to recover.
Measured in terms of abundance and species diversity, recovery is relatively fast. Many groups return to levels close to those found in old-growth forest within 30 years, and in some cases much sooner. Pollinators such as bees, along with birds and bats, show particularly rapid gains. These species move easily across fragmented landscapes, allowing them to recolonize regenerating areas early.
Species composition changes more slowly. A forest may regain its numbers without recovering its identity. While abundance and diversity can exceed 90% of old-growth levels within three decades, similarity in species composition reaches only about three-quarters of that benchmark over the same period. Full recovery, where the assemblage of species resembles that of undisturbed forest, can take much longer—often several decades, and in some cases centuries.
This matters because ecosystems depend not only on how many species are present, but on which ones. The delayed return of old-growth specialists suggests that regenerated forests may lack certain interactions for extended periods, even when they appear structurally intact.
The study separates recovery into two components: resistance and return rate. Resistance refers to how much of a community persists during disturbance. Return rate captures how quickly species re-establish afterward. The two do not track together. Some species remain present during agricultural use but recover slowly once lost; others disappear quickly but return rapidly when conditions improve.
Mobile animals such as fruit-eating birds, bats, and bees tend to score highly on both counts. Many remain present, or nearby, even during active land use. Their mobility allows them to re-enter regenerating forests early, where they have an outsized effect relative to their numbers. By dispersing seeds and pollinating plants, they help set the course of regeneration. Their presence reinforces the process: as vegetation returns, it provides resources that attract more animals, which in turn sustain regeneration.
Trees recover more slowly. They are typically removed during land conversion and return over longer timescales, constrained by long generation times and limited dispersal. Many old-growth species are rare, so even as species numbers rebound, the mix that defines an old-growth forest takes much longer to return.
Not all groups recover at the same pace. Soil bacteria show high resistance but little evidence of return, with communities remaining altered long after above-ground systems begin to resemble forest again. Leaf-litter arthropods and other less mobile organisms also recover slowly, in part due to limits on dispersal and habitat continuity.
Recovery also depends on prior land use. Forests regenerating from former cacao plantations tend to recover more quickly than those from pasture. Cacao systems, even when intensively managed, retain more structure and resources than open pasture, providing a better starting point for recolonization.
Across all groups, return rates play a larger role than resistance in determining recovery time. Recovery also depends on the surrounding landscape. Forests near intact habitat are more likely to receive a steady influx of species, which speeds regeneration. In more degraded settings, recovery may slow or stall.
Natural regeneration, which receives less attention than active restoration, can be an effective and cost-efficient strategy. But it depends on time. Many secondary forests are cleared again before they mature, limiting their value as reservoirs of biodiversity.
Old-growth forests remain irreplaceable, particularly for species that depend on long-established conditions. At the same time, in landscapes that have already been altered, allowing forests to regenerate remains one of the most practical ways to restore biodiversity.
Banner image: Scarlet macaw in Costa Rica. Frugivores are important seed dispersers. Photo by Rhett Ayers Butler
Citations:
- Metz, T. et al (2026). Biodiversity resilience in a tropical rainforest. Nature, April 8, 2026. https://doi.org/10.1038/s41586-026-10365-2
- Pain, A., Marquardt, K., Lindh, A. & Hasselquist, N. J. What is secondary about secondary tropical forest? Rethinking forest landscapes. Hum. Ecol. 49, 239–247 (2021). https://doi.org/10.1007/s10745-020-00203-y
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