From the island’s coasts to its sloping mountain ranges, Puerto Rico’s tropical forests teem with biodiversity. But these forests are even more diverse than they appear at first glance: When it comes to how they use water, trees in Puerto Rico are surprisingly individualistic.
A study published on 12 August in Nature reveals that in these forests, two trees belonging to the same species can vary wildly in how they transport, manage, and store water, depending on how dry it is in their specific habitats. The findings suggest Puerto Rico’s tropical forests may be more resilient to drought than once thought and point toward better ways to model forests’ responses to future climate change.
“Populations are indeed able to adjust to drier conditions,” says Jordi Martínez-Vilalta, a forest ecologist at the Autonomous University of Barcelona who was not involved with the research. That insight changes “the way we interpret the vulnerability of different populations within species.”
Tropical forests are essential havens for many of the world’s species, and they also hold on to enormous amounts of carbon that would otherwise go into the atmosphere as greenhouse gases. Scientists have grown concerned about drought in many tropical areas. But previous research on these forests’ resilience to that stressor tended to examine a diverse range of tree species—without necessarily assessing the variation within any given species.
To test how variable individual tree species could be, the team picked six forest sites across Puerto Rico that fell along a natural rainfall gradient. The driest site, the Guánica Dry Forest, receives only 85 centimeters of rain each year, whereas the site on the other end of that spectrum, the Luquillo rainforest, gets 450 centimeters. The team studied 18 tree species across the sites, analyzing 290 trees in total.
