Temperate plant communities in the Sierra Juárez, Oaxaca: altitudinal levels and implications associated with climate change

Abstract

Biodiversity was estimated and characterized in four temperateecosystems in Sierra Juarez, Oaxaca, Mexico: an oak-dominated chaparral,two oak forests, and a pine-oak forest (from low to high elevation).Although, the a diversity was relatively low, particularly for neespecies, species turnover was very high even between nearby stands, asindicated by the significant contribution of the 13 diversity (richness.Shannon) to total diversity. The lowest diversity of trees was found atthe lowest elevation, whereas the diversity of shrubs decreased withelevation. Tree basal area increased as the shrub cover diminished.Canopy cover, soil litter cover, and tree basal area increased withelevation where humidity is higher, suggesting that humidity is limitingbiomass. A deficit of trees in the smallest DBH class coupled with lowdensity of seedlings and small-sized individuals in all sites suggestslow recruitment in recent times. On the basis of an estimated shiftupwards of the actual rainfall levels of 175 m in altitude by 2030, wepredict the expansion of chaparral at the expense of temperate forestand the extinction of high-altitude species. Such predictions appear tohe consistent with the observed differences among study sites in sizestructure, density of saplings and standing dead trees. It is possiblethat in the near future the sierras in Oaxaca will not have the currentclimatic conditions to sustain the high altitude vegetation. Werecommend to examine the costs and benefits of active conservation inthis sierra, such as assisted migration, and genetic improving,particularly for high-altitude species.