Helping animals to reforest the tropics

Daisy Dent on why restoration efforts in the tropics might be missing the forest for the trees

June 29, 2022

As biodiversity loss and climate change roil our planet, countries are turning to forest restoration as a solution to these twin evils. Forests not only create habitat for organisms, they also soak up atmospheric CO2. In the tropics, where forest growth rates are higher than elsewhere in the world, restoring these ecosystems can lead to particularly rapid carbon uptake. As a result, many tropical countries have made voluntary commitments to restore forests over millions of hectares of degraded land.

Yet forests are complex ecosystems, which means it is still not possible to predict how fast they will regenerate—and hence their ability to mitigate climate change . Daisy Dent, an Alexander von Humboldt Fellow at the Max Planck Institute of Animal Behavior (MPI-AB) and an expert in tropical forest ecology, thinks that it’s a problem of perspective. “When people think of restoration they usually think of planting more trees, but a forest is more than its trees,” says Dent. In July, Dent and fellow ecologists Drs. Carolina Bello (ETH-Zurich) and Sergio Estrada-Villegas (Yale University) are leading a symposium at the Association for Tropical Biology and Conservation annual meeting (ATBC 2022), where they seek to bring into focus a previously overlooked player in tropical reforestation: animals.

On the International Day of the Tropics, Dent speaks to MPI-AB about how animal communities drive forest re-assembly and why, if they are left out of the picture, restoration efforts risk missing the forest for the trees.

Why is reforestation not just about trees?
There is massive impetus for forest restoration in the tropics, from the global Bonn Challenge to regional initiatives. These campaigns tend to focus on plant communities and simply planting trees, but trees alone don’t make a forest. We need to shift the focus away from planting trees and onto ecosystem recovery and how to encourage other groups of organisms to colonise and establish in regenerating forests. By doing so, reforestation efforts will generate environmental outcomes that go beyond carbon storage, like increased biodiversity and reduced soil erosion.

How can animals help reforestation?
Trees are stationary, but animals are mobile and functionally connect fragmented landscapes. As animals move, they transport biologically important items like seeds, pollen, and even mycorrhizal fungal spores. In the tropics, over 80% of tree species are dispersed by animals. This means that fruit-eating animals carry seeds across the landscape, which is hugely important when it comes to restoring natural forests. Moreover, approximately 90% of flowering plant species are pollinated by animals. When pollinators move among fragments, they bring pollen from diverse locations to restoration sites, which increase reproduction success, adaptation to local conditions, and resistance to pathogens. Therefore, promoting free movement of pollinators in restored areas is fundamental for plant reproduction and population viability. Finally, large vertebrates can influence plant recruitment and growth in recovering forests by bringing mycorrhizal fungi from the forest. Mycorrhizal fungi are ubiquitous symbionts of all terrestrial plant species. They absorb nutrients and water from the soil and transfer them to the roots promoting faster and taller growth.

A recent study showed that connectivity among protected areas is low. To boost protected areas’ connectivity, we must encourage restoration and especially animal movement inside restored areas.

How will it work?
We want to understand how to use animals to support restoration, and how to structure the landscape to enable animal movement. For example, if you plant a forest next to an existing patch, you get higher rates of diversity recovery because you have an influx of seeds from the neighboring forest. But an isolated forest is not visited by seed dispersers, and so it regenerates slowly. We want to understand how to structure restoration plantings that promote connectivity so the animals can move among the forest patches.

The most important next step is to feed this information through to restoration practitioners so they develop planting and management strategies that enable frugivorous species and pollinators to help the process. In tropical reforestation, however, the challenge goes beyond just planting the right trees in the right place. It’s also about working with the local communities to balance the benefits of reforestation with deeply rooted cultural practices.

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