Dry Tropical Forests in the Caribbean and Latin America under Threat

Inventory of woody plants reveals loss of plant diversity

Inside the dry tropical forest of the Mona Island Natural Reserve, Puerto Rico. Photo by Humfredo Marcano-Vega, U.S. Forest Service.
Inside the dry tropical forest of the Mona Island Natural Reserve, Puerto Rico. Photo by Humfredo Marcano-Vega, USFS.

The climate and fertile soils of the dry tropical forests of Latin America and the Caribbean have been important to humans as areas to grow crops since pre-Columbian times. Because of this and more recent use for intensive cultivation and cattle grazing, many of these forests have been cleared, with less than 10 percent of original dry tropical forest remaining in many countries.

Even though they support a wide diversity of species found nowhere else in the world, few dry tropical forests are currently protected, according to a study recently published in Science by scientists in the Latin America and Caribbean Seasonally Dry Tropical Floristic Network (DryFlor). U.S. Forest Service research biologist Humfredo Marcano-Vega, based in San Juan, Puerto Rico, contributed to the article.

“We define tropical dry forest as having a closed canopy, distinguishing it from more open, grass-rich savannas,” says Marcano-Vega, who works for the Forest Service Southern Research Station Forest Inventory and Analysis unit. “These seasonally dry forests grow on fertile soil where the rainfall is less than 70 inches a year, with a period of 3 to 6 months of less than 4 inches per month during which most vegetation shows deciduousness — leaf drop — as a special adaptation to water scarcity.”

Using data from 1602 inventories that cover 6958 woody species that occur in dry tropical forests from Mexico and the Caribbean to Argentina and Paraquay, the researchers evaluated the patterns of plant diversity in remaining areas of dry forest, highlighting those areas with the highest diversity and endemism (species confined to a unique location). They also looked at floristic turnover, the rate at which woody species are replaced by new ones across the geographic range of neotropical dry forests.

They found that the variation in woody species composition among inventories defined 12 dry floristic groups and that the remaining dry forests in Latin America and the Caribbean are fairly different from one another — 23 to 73 percent of the species found in each forest are distinct to it – and that there was a high level of floristic turnover across the region. This indicates that remaining dry tropical forests in all of the 12 floristic groups in the region should be protected to prevent the loss of major species diversity.

The DryFlor scientists found the current levels of protection for these forests “woefully inadequate.”

An example is the Andean dry forests, some in small patches, whose species compositions are distinct from one another and from the dry tropical forests of the rest of the region. Some of the distinct floristic groups within these forests currently have no formal protection at all and are under pressure from high local populations who clear them for agriculture and fuelwood.

“It is our hope that our data set for Latin American and Caribbean dry forests and the results shown here can become the basis for future conservation decisions that take into account continent-level floristic patterns and thereby conserve the maximum diversity of these threatened forests,” the authors write in conclusion. “Interdisciplinary viewpoints that recognize the needs of local communities and the effects of management decisions on people are also fundamental for the success of dry forest protection proposals within the region,” adds Marcano-Vega.

Read the full text of the article.

For more information, email Humfredo Marcano-Vega at hmarcano@fs.fed.us.

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