The chaparral vegetation in Mexico under nonmediterranean climate:: The convergence and Madrean-Tethyan hypotheses reconsidered

A comparative study between an unburned evergreen sclerophyllous vegetation located in south-central Mexico under a wet-summer climate, with mediterranean regions was conducted in order to re-analyze vegetation and plant characters claimed to converge under mediterranean climates. The comparison considered floristic composition, plant-community structure, and plant characters as adaptations to mediterranean climates and analyzed them by means of a correspondence analysis, considering a tropical spiny shrubland as the external group. We made a species register of the number of species that resprouted after a fire occurred in 1995 and a distribution map of the evergreen sclerophyllous vegetation in Mexico (mexical) under nonmediterranean climates. The Tehuacan mexical does not differ from the evergreen sclerophyllous areas of Chile, California, Australia, and the Mediterranean Basin, according to a correspondence analysis, which ordinated the Tehuacan mexical closer to the mediterranean areas than to the external group. All the vegetation and floristic characteristics of the mexical, as well as its distribution along the rain-shadowed mountain parts of Mexico, support its origin in the Madrean-Tethyan hypothesis of Axelrod. Therefore, these results allow to expand the convergence paradigm of the chaparral under an integrative view, in which a general trend to aridity might explain floristic and adaptive patterns detected in these environments.