Mexico is a land of many biomes. The Tropic of Cancer makes a division of the country into tropical ,subtropical, temperate semi arid and desert biomes. There is forest, with about 70 percent in the tropical category and 30 percent in the subtropical category.
Between 1990 and 2005, Mexico lost over 11 million acres of forest for various reasons, but with conversion to agriculture and grazing as the leading causes. In some areas, classic overgrazing along with ways that water drains in mountainous regions has contributed to soil erosion, which leads to desertification.
The State of Tabasco, for example, was predominantly tropical forest in the 1940's. In the 1980s the state had less than 10 percent that was tropical forest, with most of the forest replaced by pasture.
Most of the land in the North and Northwest is seriously accellerating in erosion or is completely degraded. In an area that is already arid or semi arid, overgrazing and watering with more than normally saline water has compounded the problems.
In the tropical rainforests, deforestation and overgrazing are aggravated by high seasonal rainfall which further erodes the soil, making it unable to support the plants that keep it stable.
Overpopulation in Mexico is mainly confined to the major urban areas, but conversion of land to farming and grazing is required to sustain the huge population. Also, Mexico has an unusual and limited river system that leads to water diversion and desertification. The alternative is to support massive migration into the US, but that option is becoming increasingly untenable while the US is in international, political, environmental and economic crisis. One estimate is that around 700,000 people migrate from the deserts during the dry season every year.
Climate change is having an impact on land that is already desertified or in progress of desertification. Extended periods of drought are not helping matters, but when the soil is so depleted that there are no nutrients to sustain plants, more must be done to lower levels of pollution which are out of control in some highly populated major urban areas, such as Mexico City. The pollution of the major population centers plays a role in desertification from acid rain, which damages the plants that hold soil together.
Mexico has not been ignoring the issue of desertification. Since the 1980s, there has been much work to study deforestation, water diversion and management, climate change, overgrazing and other issues that have contributed to desertification since the 1980s. For 2010, Mexico is working to craft a new environmental law, a forest law and technical assistance programs are being developed.