Patterns of vegetation along contrasting elevation gradients in Oaxaca and Veracruz, Mexico

Abstract

Elevation gradients have been widely documented, but few studies have compared patterns of variation between contrasting transects. Our objective was to compare vegetation structure and tree species composition of forest communities on 2 extended gradients located along the Pacific coast (Oaxaca, 0-3,600 m), and the Gulf of Mexico coast (Veracruz, 70-4,000 m), Mexico. We established 21 one-ha plots on each gradient. A total of 4,229 trees were measured and identified. Results showed that with increased elevation, basal area decreased unimodally in Oaxaca, and increased monotonically in Veracruz, whereas taxa richness decreased non-linearly in both gradients. Oaxaca was warmer and drier than Veracruz, however, richness was higher in Oaxaca (260 species) than in Veracruz (210 species). A multinomial classification model identified 58 species as Oaxaca specialist and 41 as Veracruz specialists, but only 12 species were generalist in both gradients. Canonical correspondence analyses for species, genus, and family consistently separated dry forests related to temperature and potential evapotranspiration from high elevation conifer forests. Mid-elevation montane forest differed between gradients. We conclude that climate is differentially important in vegetation structure and taxa distribution, but geographical location and disturbance history should be discussed for each gradient.