Fewer People = Less Biodiversity?

Across South and Central America, forests are reclaiming large swathes of countryside as rural residents move to the city. The migration trend is often seen a boon for biodiversity, as fewer people can mean less hunting, fishing, logging and land clearance. A provocative new study from Mexico’s southwestern highlands, however, argues that fewer people could be bad for biodiversity.

Researchers often assume that “forest gain necessarily equates with biodiversity conservation,” James P. Robson and Fikret Berkes of the University of Manitoba, Canada, write in Global Environmental Change. Their field work in two small traditional farming communities in the Mexican state of Oaxaca, however, have caused them to “question this assumption.” Both communities – San Juan Evangelista Analco and Santiago Comaltepec – sit in the rugged ridges and steep valleys of northern Oaxaca , and both have seen extensive “outmigration” of residents to the United States and Mexican cities. To better understand the consequences of these shifts, the researchers extensively surveyed residents and land-use changes in the two communities.

Overall, they found that local farmers have abandoned many fields, allowing forests to regrow. Today, “as across much of Oaxaca, fewer people are farming,” they write. “Farmers are cultivating less land, working closer to settlements, and growing fewer crop varieties.” That has triggered “unprecedented changes in ecological succession,” they note, including changes in the size of forest and grassland patches, and the availability of “edge” habitats favored by many organisms.

Although they did not collect specific data on the region’s biodiversity, they “speculate” — based on work in other parts of Mexico showing that traditional farming practices have helped promote diverse ecosystems — that the changes could result in the “gradual loss of the forest–agriculture mosaic, leading to localized declines in biodiversity, despite (or because of) extensive forest resurgence.”

They concede that the idea “goes against the grain of conventional conservation thinking,” and write that more research is needed to flesh it out. But it “adds a layer of complexity to how we perceive forest transitions in tropical country contexts…. (T)he relationship between population and the environment is neither linear nor deterministic.”

The indigenous cultures in Oaxaca “should not be seen as an environmental constraint,” they add, “but as an agent of landscape renewal and source of heterogeneity that generates biodiversity. The fact that indigenous landscapes exist in Mexico that allow for both cultural and biological diversity to flourish is something that national and international conservation bodies need to more fully recognize and incorporate into future policies and initiatives.” David Malakoff | May 23, 2011

Source: Robson, J., & Berkes, F. (2011). Exploring some of the myths of land use change: Can rural to urban migration drive declines in biodiversity? Global Environmental Change DOI: 10.1016/j.gloenvcha.2011.04.009

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