Many studies have focused on how climate change leads to biodiversity loss—but MIT researchers have now shown that the reverse is also true: declining biodiversity can undermine one of the planet’s strongest natural defenses against climate change.
In a paper published in PNAS, the team found that naturally regenerating tropical forests with thriving populations of seed-dispersing animals can store up to four times more carbon than similar forests where those animals are scarce.
New Insights into Biodiversity’s Role in Strengthening Tropical Forest Carbon Storage
Since tropical forests serve as the world’s largest land-based carbon sinks, the research offers new insight into how biodiversity helps combat climate change.
“These findings highlight the critical role animals play in sustaining carbon-dense tropical forests,” says lead author Evan Fricke, a research scientist in MIT’s Department of Civil and Environmental Engineering. “If populations of seed-dispersing animals fall, we risk reducing the ability of these forests to mitigate climate change.”
Fricke’s co-authors include MIT’s César Terrer and Charles Harvey, along with Susan Cook-Patton from The Nature Conservancy.
The study integrates extensive data on animal biodiversity, movement patterns, and seed dispersal from thousands of species, along with carbon storage measurements from numerous tropical forest sites.
According to the researchers, their findings offer the strongest evidence to date that seed-dispersing animals significantly influence forests’ capacity to capture carbon. The results emphasize the importance of viewing biodiversity loss and climate change as interconnected challenges within a complex ecological system—not as isolated issues.
“While it’s well known that climate change threatens biodiversity, this research reveals how biodiversity loss can, in turn, intensify climate change,” says Fricke. “Recognizing this two-way relationship helps us better understand these intertwined crises and how to address them. Protecting biodiversity and combating climate change aren’t mutually exclusive—this study shows that advancing one can directly support the other.”
Connecting The Dots
The next time you watch a monkey or bird nibble on fruit, remember they’re doing more than just snacking—they’re performing a key ecological service. Research shows that by consuming fruit and later depositing the seeds elsewhere, these animals support plant germination, growth, and long-term survival.
Fricke, who has spent nearly 15 years studying animal-driven seed dispersal, has previously found that trees without animal help face reduced survival rates and struggle more to adapt to changing environments.
“We’re increasingly exploring how animals might influence the climate through seed dispersal,” Fricke explains. “In tropical forests—where over 75% of trees depend on animals to spread their seeds—a drop in seed dispersal doesn’t just threaten biodiversity. It also weakens the forest’s ability to recover from deforestation. And globally, animal populations are declining.”
While reforesting is widely promoted as a strategy to combat climate change, the role of biodiversity—particularly the presence of seed-dispersing animals—in boosting forests’ carbon absorption has been largely overlooked, especially on broader scales.
Comprehensive Analysis Reveals How Human Impact Alters Seed Dispersal in Tropical Forests
For their research, the team drew on data from thousands of individual studies and applied new methods to quantify complex, interrelated ecological processes. After examining over 17,000 vegetation plots, they chose to focus on tropical regions, analyzing where seed-dispersing animals live, how many seeds each species disperses, and the impact of that activity on seed germination.
They also factored in data on how human activity affects the movement and presence of these animals—finding, for instance, that animals tend to travel shorter distances when consuming seeds in areas with significant human disturbance.
Using this information, the researchers developed a seed-dispersal disruption index, which revealed a clear link between human activity and reductions in animal-driven seed dispersal. They then examined how this index correlated with long-term carbon accumulation in naturally regrowing tropical forests, while accounting for variables like drought, fire frequency, and grazing.
“Bringing together data from so many field studies to map disruptions in seed dispersal was a major undertaking,” Fricke says. “But doing so allowed us to move beyond identifying which animals are present—we were able to measure their ecological functions and see how human pressures interfere with those roles.”
The researchers acknowledged that limitations in the available data on animal biodiversity introduce some uncertainty into their conclusions. They also pointed out that other ecological factors—like pollination, seed predation, and competition—affect seed dispersal and may influence how forests regenerate. Nonetheless, their results align with recent estimates in the field.
“What sets this study apart is that we’re now able to quantify these effects,” Fricke explains. “The fact that disruptions in seed dispersal account for a fourfold variation in carbon uptake across thousands of tropical forest regrowth sites highlights the significant role seed-dispersing animals play in regulating forest carbon.”
Measuring Carbon Loss
In forests identified as suitable for natural regrowth, the researchers found that declines in seed dispersal were associated with an average yearly reduction of 1.8 metric tons of carbon absorbed per hectare—representing a 57% drop in regrowth potential.
Their findings suggest that natural forest recovery is most effective in areas where seed-dispersing animals remain relatively undisturbed. These include recently deforested regions, places near well-preserved forests, or landscapes with substantial existing tree cover.
“When comparing tree planting with natural regrowth, the latter is essentially free, while planting is costly and often results in less diverse ecosystems,” says Terrer. “Thanks to these findings, we can now better identify areas where natural regrowth is likely to succeed because animals are ‘planting’ seeds on their own—and where, due to animal decline, active tree planting becomes necessary.”
To help maintain healthy populations of seed-dispersing animals, the researchers recommend strategies like protecting habitats, creating wildlife corridors, and regulating wildlife trade. They also suggest reintroducing lost species or planting tree species that attract seed dispersers to restore their ecological role.
“Failing to account for the effects of disrupted seed dispersal could lead to overestimating natural regrowth potential in some regions and underestimating it in others,” the authors note.
Findings Highlight Urgency to Study Declining Carbon Uptake in Tropical Forests
The team sees their findings as opening new directions for research. “Forests offer a massive climate benefit by absorbing around one-third of human-generated carbon emissions,” says Terrer. Tropical forests are the world’s most vital carbon sink, yet their carbon uptake capacity has declined in recent decades.
Our next step is to investigate how much of that drop is due to increasing droughts and wildfires versus the loss of animal-driven seed dispersal.
More broadly, the researchers hope this work deepens understanding of the intricate relationships that sustain Earth’s ecosystems.
“When we lose animals, we’re dismantling the ecological framework that supports the health and resilience of tropical forests,” Fricke adds.
The study was funded by the MIT Climate and Sustainability Consortium, the Government of Portugal, and the Bezos Earth Fund.
Read the original article on: MIT
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