Exploring some of the myths of land use change: Can rural to urban migration drive declines in biodiversity?

Forest transition theory describes a reversal in land-use trends for a given area, from a period of net forest area loss, to a period of net forest area gain. Some assume that such forest gain necessarily equates with biodiversity conservation. We question this assumption, based on research conducted in Oaxaca, Mexico. In Oaxaca's northern highlands, low intensity forest use and rotational (milpa) agriculture have led to pronounced spatial heterogeneity in forest structure and composition, and created a high-biodiversity forest–agriculture mosaic. In the Zapotec community of San Juan Evangelista Analco and the Chinantec community of Santiago Comaltepec, as across much of Oaxaca, fewer people are farming; farmers are cultivating less land, working closer to settlements, and growing fewer crop varieties. Widespread agricultural abandonment has initiated unprecedented changes in ecological succession, patch size, and edge effects, which we speculate will be having an impact on the biodiversity of the landscape mosaic. Our work suggests that the decline of land use activity may result in a gradual loss of the forest–agriculture mosaic, leading to localised declines in biodiversity, despite (or because of) extensive forest resurgence. These findings support the view that indigenous cultures in Oaxaca and Mexico should not be seen as an environmental constraint but rather as an agent of landscape renewal that allows for both cultural and biological diversity to flourish, a reality that national and international conservation bodies need to more fully recognise and incorporate into policy.

► Discusses how rural landscapes are impacted by rural depopulation in Oaxaca, Mexico.
► Widespread agricultural abandonment has initiated a process of ecological succession on a scale unheard of previously.
► Changes in ecological succession, patch size and edge effects are impacting wild and agricultural biodiversity.
► Hypothesises that extensive forest resurgence will result in a gradual loss of forest–agriculture mosaic and localised declines in biological diversity.
► Indigenous culture in Oaxaca is not an environmental constraint but rather an agent of landscape renewal that allows for both cultural and biological diversity to flourish.