Fragmentation limits the natural regeneration of tropical forests

Although natural regeneration is more cost-efficient and ecologically beneficial, it’s not always feasible. Quantifying the point at which the natural recovery of forests becomes unrealistic and intervention is needed can help improve the way we plan for forest restoration.

A recent simulation study aims to quantify the potential for natural regeneration in tropical forests by looking at frugivorous birds and their movements in the highly fragmented Atlantic Forest in southeastern Brazil. Individual-based models were used to look at the potential for seed dispersal from a range of bird species in open areas across a gradient of forest fragmentation. These models provided outputs that explored how forest fragmentation and isolation, along with species traits, impact seed dispersal and the potential for carbon storage.

The results show that the amount that frugivorous birds contribute to potential seed rain and carbon storage restoration changes along the fragmentation gradient. Increasing forest cover led to greater seed deposition and greater potential above ground biomass. Increasing forest isolation led to the opposite effect. When comparing seed deposition across the fragmentation gradient, landscapes with higher fragmentation had the potential to hold almost 40% less carbon than those that had less fragmentation.

Fragmentation also affected bird species differently. Large birds contributed more to seed dispersal in open areas, although their movements were more limited once the forest cover dropped below 40%. While smaller birds were likely to disperse more seeds, especially in highly fragmented landscapes, they tended to disperse seeds of species that have lower carbon storage potential.

Since tropical ecosystems are highly dependent on seed dispersal by animals to regenerate, these results highlight how important it is to keep tropical forests connected. Maintaining a forest cover of greater than 40% is the limit of what some animals may need to contribute effectively to natural forest regeneration and help boost carbon storage. In a more fragmented ecosystem, active restoration by human intervention is likely needed to help forests regrow.

Studies like these provide targets for determining whether tropical forest ecosystems can recover on their own from fragmentation. Identifying the composition and configuration of landscapes that help or hinder animals’ contribution to seed dispersal can lead to more successful restoration strategies. Targeting restoration for specific species that contribute most to restoration goals can help boost biodiversity and potentially mitigate climate change impacts. Maintaining forest connectivity, particularly in tropical regions, represents a key component of maintaining functional ecosystems into the future.

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