Environmental correlates of tree and seedling-sapling distributions in a Mexican tropical dry forest.

摘要

Bray and Curtis ordination was used to explore which environmental variables explained importance values and the presence-absence of tropical tree seedlings, saplings and adults in La Escondida-La Cabana, Sierra de Manantlan, Jalisco, Mexico. The diameters of trees >=2.5 cm DBH and the presence and height of seedlings and saplings were measured in nine 0.1 ha sites. Four matrices including presence-absence data and importance value indices for trees and seedlings and saplings were analyzed through Bray and Curtis ordination. The matrices were based on density, frequency, and dominance of adult trees as well as seedlings and saplings. The environmental matrix consisted of 18 variables, including elevation, slope, canopy gaps, disturbance, and soil variables. We recorded 63 tree species and 38 seedling and sapling species in the nine sites. The ordination explained 70.9% of the variation in importance value data for trees and 62.6% for seedlings and saplings. The variation explained in presence-absence data for trees was 67.1 and 77.4% for seedlings and saplings. The variance in the ordination axes of seedlings and sapling presence-absence data was poorly explained by the number of gaps in the tree, shrub, or herb layer, suggesting little light specialization by seedlings and saplings. Habitat specialization for soil nutrients appears to be important in explaining the presence-absence of seedlings and saplings. Seedling and sapling specialization along different soil microsites could promote species coexistence in this forest, while heterogeneity in light conditions may instead determine differences in growth and, thus, importance value of trees. We hypothesize that in tropical dry forest in Jalisco, Mexico, a habitat specialization for soil resources is likely more importance at early stages in tree life histories than in later life history..