Evolution of disturbed oak woodlands: the case of Mexico City's western forest reserve

Mexico City is the largest city in population and area in the world. In the last 30 years it has expanded its area westwards to include the mountains of the Sierra de las Cruces. These mountains contain the nearest forest reserve for the citizens of Mexico City. Deforestation and severe ecological degradation resulting from the destruction of the natural environment; air, water and soil pollution; and hydrological and geomorphological imbalances, limit the capacity of these areas to support forest regeneration. This study focuses on the geo-ecology of the climax oak woodlands found in the Sierra de las Cruces. Based on morpho-structural evidence, bioclimatic type, degree of human intervention and general geo-ecological considerations, three territorial systems have been differentiated in which the oak woodlands exist in different climax facies: a) oak woodlands developed in very humid and cool environments located on low mountain slopes; b) disturbed oak woodlands developed in humid and cool environments located on high piedmonts; and c) highly disturbed oak woodlands developed in subhumid and temperate environments, located on low piedmonts. A comparative study of the content, structure and functional relationships of the secondary facies associated with these climax communities, allowed conclusions to be drawn on the way oak woodlands respond to human intervention, and the risky situations to which these communities are subjected, particularly the most sensitive facies that deserve immediate protection.