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Humans, Not Climate Change, Had Larger Impact on Segment of Amazon Forest

New Research Studied 7,000-Year-Old Tropical Forest in Peru

MELBOURNE, FLA. — How do human disturbances and climate change affect tropical forests? An international research team, including ecologists from Florida Institute of Technology and University of Amsterdam, looked into the 7,000-year history of a tropical Amazonian forest and found that human disturbance, more than climate change, affected the species composition of tropical forests over the last millennia.

The results, including important implications for forest management, were published March 18 in Ecology Letters in the paper, “A 7000-year history of changing plant trait composition in an Amazonian landscape; the role of humans and climate.”

Humans and climate change both affect the species composition and productivity of tropical forests, with consequences for biodiversity and carbon storage potential. The characteristics of species that determine how much carbon they store, how fast they grow, or how hard their wood is are known as plant functional traits. Tracking how plant functional traits have changed in Amazonia, which alone stores the equivalent amount of carbon each year as all vehicles emit, is an important piece in the global warming puzzle.

The new study now links the functional plant trait data with a 7,000-year-old fossil pollen record of forest dynamics in Lake Sauce in the Peruvian Amazon.

“We expected that the trait composition of tropical forests would respond strongly to both climate change and human disturbances. To our surprise, the community trait composition responds more strongly to human disturbances than to climate change,” said Masha van der Sande, tropical ecologist at the University of Amsterdam Institute for Biodiversity and Ecosystem Dynamics and at Florida Tech and lead author of the study. “We found that human-induced erosion increases the relative abundance of tree types that demand fewer resources, with dense wood, while human-induced fire enhanced the relative abundance of tree types that can survive or escape fire, like tall species with large seeds.”

The results indicate that forest management decisions to reduce and regulate human influence will be important for protecting tropical forest ecosystems. Other studies have shown that human influence strongly decreased after European arrival, leaving the forests to recover and sequester large amounts of carbon from the atmosphere. Current and predicted increases in human disturbance, however, may reverse this effect and expose the forest to strong changes in composition and carbon sequestration capacity.

Mark Bush, a biology professor at Florida Tech and co-author of the paper, said, “Understanding that human actions and decisions can have such a large role in Amazonia’s carbon budget, and therefore on global warming, is encouraging. We have identified that this portion of global climate change can be addressed through policy and education.”

The article is available at https://onlinelibrary.wiley.com/doi/10.1111/ele.13251.

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