Researchers identify human activities as factors in biodiversity decline in central Mexico reserves

New research shows that the diversity of plant and animal life in 14 tropical reserves in Mesoamerica has fallen since 1990 as roads and cattle ranches have expanded into protected areas. Large mammals, birds and reptiles are disappearing, while disease-carrying insects and rodents are increasing.

Even these highly protected areas see the range of plant and animal life following a now global trend in which a few groups thrive and proliferate in human-altered landscapes where most groups decline.

“We had the idea that this was happening on a global scale. What’s surprising is how pervasive this phenomenon of winners and losers is in tropical areas,” said the lead author of the paper. study, Rodolfo Dirzo, professor of biology at the Stanford School of Humanities and Sciences, and of earth system science at the Stanford Doerr School of Sustainability. “This is crucial because tropical rainforests constitute the most important reserves of biological wealth on the planet.”

The research is based on surveys of more than 60 tropical ecologists who, like Dirzo, have spent decades studying reserves in central Mexico. The 14 reserves studied, part of a biodiversity hotspot that stretches across Mesoamerica, were each designated as part of a UNESCO program aimed at establishing a scientific basis for improving the means livelihoods and safeguard ecosystems.

In and around many protected areas, the authors found that new roads continued to rise and trees fell between 1990 and 2020, as people cleared the forest for timber or livestock grazing. The abundance of long-lived, shade-tolerant tree species – those that make old-growth forests one of our planet’s greatest carbon sinks – has declined by an average of more than 25% in all reserves.

“What’s left are just little pieces of forest, and a lot of disturbance around them,” said the study’s lead author, Daniel Auliz-Ortiz, who worked on the research as part of his doctoral thesis at the Universidad Nacional Autónoma de México in Morelia. Mexico.

According to the study published on January 22 in the Proceedings of the National Academy of Sciences, the fragmented and depleted habitats that remain no longer support populations of primates, many butterflies, raptors, reptiles, amphibians and large predators like jaguars in the numbers they once did. In their place, small, fast-breeding animals like rats and mice and weedy, light-loving vines thrived.

A global challenge

The ongoing changes in tropical forest reserves in central Mexico illustrate a reality of protected areas around the world: deforestation is rarely completely eliminated, with major negative consequences for ecosystems and humans.

Small rodents carry many infectious diseases that can spread and prove dangerous to humans. As prolific seed growers, they can also change where and how various plants become established in an ecosystem, added Dirzo, a senior scientist at the Stanford Woods Institute for the Environment and the Bing Professor of Environmental Science. “We’re positioning them to be the winners in these ecosystems,” he said.

Also among the winners are fast-growing pioneer plants that need abundant light and can benefit from disturbed or clear-cut landscapes, but which store far less carbon than shade-tolerant tree species that they replace. This replacement “can significantly limit global carbon storage,” the authors write.

Expand opportunities

To prevent further deforestation, researchers call for expanding opportunities for people to earn a living around protected areas by means other than livestock farming. They found that rates of forest loss were lower and human well-being higher in regions where economies revolve around alternatives such as environmentally friendly tourism, public programs that compensate local communities for the environmental services provided by intact forests, or the cultivation of multiple crops such as coffee and coffee. cocoa in the shade of a forest cover.

In the absence of these opportunities, researchers have found that local communities often turn to intensive livestock farming or monoculture and are forced to cultivate more and more land to remain profitable.

“Protection is not a panacea,” Dirzo said. “We need to ensure that the areas we have set aside are not just reserves on paper, but that they effectively protect biodiversity within landscapes where the livelihoods of local people are also meaningfully supported.”