Birds and bats sow tropical seeds

September 13, 2005

Restoring the rich diversity of trees that once characterized expansive tracts of tropical rainforest gets a helping hand from native birds and bats. Just how big a role these winged gardeners play is a question ecologists from the University of Illinois at Chicago and several Latin American universities are about to find out by setting up essentially a living laboratory in Mexico's gulf coast state of Veracruz.

Henry Howe, a noted authority in restoration ecology and a professor of biological sciences at UIC, will lead the multi-year test, funded initially by a five-year, $500,000 grant from the National Science Foundation. Co-investigators include Christina Martinez-Garza, a biologist on the faculty of the Autonomous University of Morelos in Mexico, and a former doctoral student of Howe's at UIC; Martin Ricker, director of the biological station in Los Tuxtlas, Veracruz and a former UIC student; and Rodolfo Dirzo, the Bing Professor in environment science at Stanford University.

The group will work closely with UNAM, the Universidad Nacional Autónoma de México, which owns and runs the Veracruz biological station.

"The point of the project is to restore diversity to agricultural landscapes," said Howe. "We'll test the proposition that immigration of trees into this tropical landscape, the remnants and forest fragments that still exist in it is dispersal-limited. That is, the seeds don't get there."

Howe said most tropical areas re-vegetate naturally after being abandoned, or by replanting a limited number of fast-growing trees that rely on the wind for seed dispersal. Replanting often leads to monocultures that support only a limited variety of animal species. Poor lands are more likely to be abandoned. Better land parcels get replanted.

But if nature had her way, more than 90 percent of replanted species would be dispersed by birds, bats and primates. That's less and less the case today in tropical areas worldwide, leading to a destructive cycle of land fragmentation, habitat loss and -- even with replanting using wind-dispersed trees -- species loss.

Howe and his colleagues will lease 16 land parcels in Veracruz located near or adjacent to forest remnants or UNAM's protected rainforest to observe what trees grow, and why. Some tracts will be planted with 12 species of animal-dispersed trees, which will ultimately provide living bait with crops of bat- and bird-dispersed fruits.

Birds and bats living in nearby forests will fly to the bait to eat the fruit and will likely drop seed from forest species they carried. Fruit will be available all year, so a seasonal progression of seeds from longer-living deep forest species should be carried with the bats and birds. Other tracts will be planted with wind-dispersed trees and will be far less likely to accumulate tree species from nearby forests.

"In the tropics, things grow fast," said Howe. "By the end of the first five years, we'll begin to see the influence of animal and wind dispersal. In 10 years, we'll see a very strong effect of seed fall, germination and establishment. Once these stands of animal-dispersed trees have grown up and start producing fruit, they'll be exporting their seeds to surrounding landscapes."

Over the coming years, tree growth in adjacent forest remnants will be studied. Howe suspects that evidence will support the hypothesis that birds and bats transport a rich mix of tree seeds, including the more enduring deep forest species.

"It's a way of providing connection between existing, isolated trees, remnants and fragments and large tracts growing along rivers in rain forests," he said.

"I think what it will show is that the replanting that almost everybody does in (tropical regions) is an extremely inefficient way to maintain and promote species diversity."

Howe hopes the project -- which he expects will run for 20 years or more -- will attract additional funding sources. And he predicts close academic collaboration between UNAM and U.S. ecology programs like UIC's.

"It will involve environmental issues which will occupy a great many students," he said. "These students will disperse through Mexico and the rest of Latin America. We hope they will carry the banner of experimental restoration of diversity into landscapes, wherever they go."
-end-


University of Illinois at Chicago

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