As the UN climate talks draw to a close in Egypt and biodiversity talks begin in Montreal, attention turns to restoring forests as a solution to the twin evils plaguing our planet. Forests absorb atmospheric carbon dioxide while creating habitat for organisms. So far, efforts to help forests recover from deforestation have typically focused on increasing one thing—trees—above all else. But a new report uncovers a powerful but largely overlooked driver of forest recovery: animals. The study, by an international team from the Max Planck Institute for Animal Behavior, the Yale School of the Environment, the New York Botanical Garden and the Smithsonian Tropical Research Institute, examined a series of regenerating forests in central Panama over a period of 20 to 100 years after the abandonment. The unique long-term dataset showed that by carrying a variety of seeds into deforested areas, animals are key to restoring the richness and abundance of tree species to old-growth levels after only 40-70 years of regrowth. The article published in Philosophical Transactions of the Royal Society Bis part of a themed issue focused on restoring forest landscapes as part of the UN Decade on Ecosystem Restoration.
“Animals are our greatest allies in reforestation,” says Daisy Dent, MPI-AB tropical ecologist and lead author of the study. “Our study encourages rethinking reforestation efforts to go beyond establishing plant communities.”
The report also notes that locating regenerating forests near patches of mature trees and reducing hunting encourages animals to establish and establish themselves. “We show that considering the broader ecosystem as well as landscape features improves restoration efforts,” says Sergio Estrada-Villegas, a biologist at Universidad del Rosario (Bogotá, Colombia) and first author of the study.
Seed dispersal by animals is key to forest expansion. In the tropics, over 80% of tree species can be spread by animals transporting seeds across the landscape. Despite this, forest restoration efforts remain focused on increasing tree cover rather than restoring the animal-plant interactions that underpin ecosystem functioning. “Finding out how animals contribute to reforestation is prohibitively expensive because you need detailed information about which animals eat which plants,” says Estrada-Villegas.
The forest at the Barro Colorado Nature Monument (BCNM) in the Panama Canal offers a unique solution to this problem. In one of the best-studied tropical forests in the world, generations of scientists have documented frugivore interactions to understand which groups of animals drive out which tree species.
In the present study, the team led by Estrada-Villegas and Dent examined this unique long-term data set to determine the proportion of plants spread by four groups of animals — flightless mammals, large birds, small birds and bats — and how The proportion varied over a century of natural recovery.
Their results provide the most detailed data on animal seed dispersal recovery over the longest period of natural recovery. “Most studies examine the first 30 years of succession, but our 100-year data gives us a rare insight into what happens in the late phase of the restoration,” says Dent.
The study found that young regeneration forests consisted mostly of trees scattered by small birds. But as the forest aged, trees driven away by larger birds increased. Surprisingly, however, the majority of plants were distributed by terrestrial mammals across all forest ages – from 20 years of age to old age. “This result is quite unusual for post-agriculture regenerating forests,” says Dent. “It is likely that the presence of large areas of protected forest near our secondary stocks, coupled with low levels of hunting, has allowed mammalian populations to thrive and bring an influx of seeds from neighboring patches.”
Estrada-Villegas says, “We hope this information can help practitioners structure their restoration practices by empowering frugivorous species to support the restoration process and accelerate forest recovery.”
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