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Tropical biodiversity faces intersecting threats

25 July 2019

As the world warms and land use changes, many rainforest species could struggle to find new habitats.

Over the past half century, the Amazon rainforest has lost some 20% of its area, mostly to livestock farming. Other tropical forests around the world have suffered a similar fate. Rainforests are home to an estimated 50% of Earth’s terrestrial plant and animal species, including unknown numbers that have yet to be discovered. As deforestation continues, those species could be lost.

A sloth in a tree
A sloth in Puerto Viejo, Costa Rica. Credit: Nacho Such/

That’s not news, of course: Rainforest conservation movements have been around for more than 30 years. But now, as part of her PhD research at the University of Sheffield, Rebecca Senior has worked with colleagues to probe the problem from a new angle: the intersection of deforestation, climate change, and species migration.

As the world warms, species will find themselves increasingly ill adapted to their current homes. Although reptiles and amphibians are especially threatened by the changing climate because they rely on their environment to regulate their body temperature, they’re not the only ones at risk. Species may be able to cope by moving to cooler habitats—either farther from the equator or uphill—but only if they can find an unobstructed path to get there.

By combining maps of tropical forest cover, current climate, and future climate projections, Senior and colleagues calculated the best available paths to cooler climates from starting points throughout the world’s rainforests. They found that under a scenario with an average worldwide warming of 4 °C, less than two-fifths of rainforest area is connected, within the bounds of the forest, to a region with an analogous future climate. Most species can do no better than to migrate to regions that are 2.2–2.9 °C warmer than their current habitats. Moreover, those numbers have gotten worse just since the year 2000.

As any researchers do when they attempt to predict the future, Senior and colleagues had to make some assumptions. For example, they used average annual temperature as their sole measure of local climate. That’s not because other variables, such as temperature extremes and precipitation, aren’t important, but because they’re so difficult to project with sufficient precision.

The analysis ends on an optimistic note. Although human land-use patterns are part of the problem in tropical species’ future, they can also be part of the solution. Preserving relatively small but carefully chosen areas of rainforest could do a lot to help connect species with their new habitats. (R. A. Senior, J. K. Hill, D. P. Edwards, Nat. Clim. Change, 2019, doi:10.1038/s41558-019-0529-2.)

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