Background:

The genus Quercus has a keystone role in the temperate forests in the northern hemisphere; thus this offers an interesting opportunity to use it as a model to know altitudinal species richness patterns which could be used in further studies and projects in biodiversity conservation.

Questions:

It is possible to detect an altitudinal gradient based on the genus Quercus distribution? What climatic variables are most important in the altitudinal distribution of the genus Quercus?

Study site:

The physiographic province of Sierra Madre del Sur (SMS) located southwest of Mexico.

Methods:

Based on 3,267 herbarium registers of 61 species, a data matrix was created with the presence/absence of each species in altitudinal intervals of 100 m. Then a similarity matrix was obtained using the Sorensen-Dice index in the R software. Through a discriminant analysis, we evaluated for environmental differences among the altitudinal zones previously obtained through a cluster analysis.

Results:

We found three altitudinal zones, each one defined by exclusive species, and two important species turnover points. The species richness distribution showed a hump-shaped pattern along the altitudinal gradient. The overall model was highly significant, evidencing the existence of different temperature and precipitation regimes throughout the altitudinal distribution of oaks species in SMS.

Conclusions:

The altitudinal distribution of oak species in the SMS is not homogeneous and is restricted mainly due to differences in the precipitation and temperature regimes. The altitudinal distribution pattern found in this study could be explained considering ecological and historical factors.