Historical State

Yifan Yu

Tropical dry forest mainly consists of deciduous trees with low to medium sizes and has a sharp contrast between its desolateness in dry seasons and exuberance in its rainy seasons (Becerra, 2005) There are little direct information about the origin of Mexican tropical dry forest, yet based on a research on temporal and spatial changes of Bursera, a dominant member of this ecosystem, scientists infer that tropical dry forest in Mexico probably originated between 30 and 20 million years ago and initially mainly appeared in the west part of Mexico and lately gradually expanded to south and central parts. (Becerra, 2005) Besides, according to Rzedowski, historically tropical dry forest may have occupied an area of nearly 270 000km², which means covering about 14% of the Mexican territory(as cited in Trejo& Dirzo, 2000). 

The colored part in the following picture show the distribution of original Mexican tropical dry forest according to Rzedowski’s analysis of potential vegetation. 

The status of conservation (sensu Oropeza et al., 1995) of seasonally tropical dry forest (SDTF) in relation to its potential distribution area (sensu Rzedowski, 1990)

source: Trejo & Dirzo, 2000

Additionally, Castillo, Magana, Pujadas, Martinez and Godinez (2005) point out that the history of tropical dry forests in the Chamela-Cuixmala region, a major area of this ecosystem in Mexico, can roughly be categorized into four distinct periods, which may provide us with a general idea of how the whole Mexican tropical dry forests interact with human through the years. In their view, until around 1800, tropical dry forest remained intact without much human disturbance and in the late 19th century, human began to exploit this ecosystem for cultivation and domestication, while the impacts resulted were relatively small. However, around 1950 with supportive policies from the administration, huge areas of tropical dry forest were conversed into agriculture fields and livestock pastures, resulting in seriously negative impacts on forests. Such large area of  transformation lasted for nearly 30 years and until around 1990, situation started to slightly improve.