New method developed for estimating biodiversity based on tree cover

Researchers at Stanford University in the United States have used tree cover maps and on-the-ground observations to measure biodiversity in Costa Rica, generating a method of modeling biodiversity across tropical landscapes.

Over a series of three- to six-month field sessions across 10 years, a team of 15 researchers hiked across the hilly tropical agricultural landscape of Coto Brus, an area in Costa Rica, making a total of 67,737 observations of 908 species, comprised of understory plants, non-flying mammals, bats, birds, reptiles and amphibians.

The Stanford team plotted their plant and animal observations on detailed, fine-scale maps from Google Earth aerial photographs, and then analyzed the results, recognizing that for four of the six species groups, namely plants, non-flying mammals, bats and birds, there was significant increase in the number of species with increasing tree cover visible on the maps.

At a single point, the new model predicts biodiversity in the region within a 30- to 70-meter radius and demonstrates how the number and kind of species change. Analysis showed that adding a single tree to pasture could boost the species number of bird from near zero to 80. After the initial sharp increase, adding trees continues to add new species, but more gradually. As the tree cover approaches 100 percent, endangered and at-risk species like wildcats and deep forest birds begin to appear.

"All the animals agreed: trees are great," said Chase D. Mendenhall, a postdoctoral research fellow in biology at Stanford and a lead author in a study published this week in the Proceedings of the National Academy of Sciences.

While the researchers found strong relationships between trees and species in Coto Brus, the question of greater applicability remained. To address this, Mendenhall and his colleagues compared their results to 90 similar studies across Latin America, finding that there were similar relationships between biodiversity and tree cover.

Calling it "a win-win situation for planting trees and reforestation," Mendenhall said the researchers are "giving people a way of measuring biodiversity, so that they can place their own value on it."

"Biologists all work with different animals. Some view the world through birds, some through bats. I'm trying to get a consensus that one thing all biologists can recommend to policymakers interested in halting climate change, protecting water, and safeguarding biodiversity is to plant, preserve and regenerate trees in the warm, wet areas of the world where most biodiversity exists," he was quoted as saying in a news release from Stanford. Endit