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NIEVES-HERNANDEZ, Gregorio et al. Small-scale environmental gradients in a pine-oak forest community in Nueva Colonia, Mezquitic, Jalisco, Mexico. Polibotánica [online]. 2009, n.27, pp.31-52. ISSN 1405-2768.

We explored environmental variables related to pine-oak forest community structure at one locality in Jalisco, Mexico. We used an NMS ordination in conjunction with the Sørensen distance to identify the major small-scale community gradients along 25 contiguous quadrats (25 m x 25 m, 400 m2 each) of pine-oak forest in Nueva Colonia, Mezquitic, Jalisco, Mexico. The main matrix (25 stands x 7 tree species) included basal area data, and the environmental matrix consisted of 19 quantitative environmental variables. Community structure, through sociological ordination, showed a direct correlation with the vertical altitudinal gradient and apparent soil density, as well as with slope inclination across the horizontal gradient; it also showed an inverse correlation with cation exchange capacity, Ca + Mg, Mg, and altitude across the horizontal gradient. Direct gradient analyses showed an increase of cation exchange capacity, Ca+Mg, Mg and K with decreasing altitude along the vertical gradient (from north to south). Total nitrogen increased with decreasing altitude across the horizontal gradient (from west to east). In addition, we identified three main community groups using UPGMA cluster analysis; however, groups were weakly related to the ordination results and to the physical space. At the 1-hectare scale, species composition and basal area of pine-oak forest in Nueva Colonia can be explained by niche partitioning of altitude and soil gradients. The relevance of nitrogen for this community could be the result of habitat specialization or disturbance history.

Keywords : calcium; magnesium; environmental gradients; habitat differentiation; niche partitioning.

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