Climatic and edaphic drivers of oak species (Quercus, Fagaceae) segregation along elevation gradients

Abstract

According to niche differentiation theory, plant species are adapted to thrive in specific segments of a heterogeneous environment, partitioning themselves along resource gradients. In this study, we analyzed the distribution patterns and the ecological importance of stand-forming species along an elevational gradient on two mountains within the Trans-Mexican Volcanic Belt (TMVB). While these mountains share a common pool of tree species, they differ in environmental conditions. First, we hypothesized that climate and edaphic factors will drive distinct species assemblages along the elevational gradients on both mountains. Second, we hypothesized that these groupings will be primarily influenced by the climatic variation along the elevational gradients. Thirty-three circular plots of 500 m 2 were characterized based upon edaphic and climatic factors. For each tree within the plots, we identified the species and recorded diameter at breast height (DBH) and height. Plots located at the lower end of the elevation gradient (below 2700 m) were warmer and drier compared to those at the upper end. Along these environmental gradients, seven oak associations were identified, each characterized by distinct habitat features including temperature, precipitation, soil bulk density ( BD ), cation exchange capacity ( CEC ), organic matter ( OM ) and phosphorous ( P ). Our results suggest that: (1) oak species segregate along axes of water and soil nutrient availability, showing maximum dominance at levels where conditions favor them; (2) species from the Quercus section prefer dry and warm habitats, while those from the Lobatae section thrive in wet and cool environments. Furthermore, our results indicate that tree height is a key trait facilitating niche partitioning, especially on smaller scales. We conclude that niche differentiation is a multiscale process facilitated by environmental heterogeneity.

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