Selective cutting of woody species in a Mexican tropical dry forest: Incompatibility between use and conservation

A major challenge of forest management is to maintain the biodiversity and integrity of the forests while at the same time satisfying human needs through productive activities. While selective extraction of natural resources has less severe consequences on biodiversity and ecosystem function than complete removal of vegetation, such consequences need to be evaluated in detail. "Varas" or stems cut from small trees of tropical dry forests (TDF) in the Pacific Coast of Mexico have been used as plant support stakes in horticultural fields (mainly tomato crops) since the middle of the last century. In this study, we evaluated the effects of selective cutting of plant support stakes on the diversity of woody vegetation of a TDF in northwestern Mexico. Stakes were cut by local harvesters before our assessment of cutting effects. In each of three cutting treatments (T-0 = uncut, T-1 = one cut event, and T-2 = two cut events), we established three sampling plots each consisting of ten 50 m x 2 m parallel transects. All woody plants (stems >= 1.0 cm diameter at 1.3 m height, DBH) were identified and measured on each transect. Species richness (S) decreased as the number of cuts increased (T-0 = 65 species, T-1 = 50 species, and T-2 = 38 species). The Simpson (C) and the Shannon (H') diversity indices, as well as the rarefaction curves and non-parametric estimates of diversity (Chao1 and ACE) confirmed this tendency of change. Comparison of dominance-diversity curves showed that the woody plant community loses equitability with every additional stake cutting event. The total number of stake providing species did not vary notably across treatments (T-0 = 8 species, T-1 = 9 species, and T-2 = 7 species), but four species reduced their dominance considerably in T-2, while Croton septemnervius, the most used species, increased its abundance and relative basal area with each additional stake harvest, reaching a representation of more than 59% of total number of stems in T-2. The reduction in species diversity, changes in patterns of dominance, and the proliferation of species associated to disturbed sites suggest that current practices of selective cutting require adjustments to make this forest management application more consistent with local conservation of woody plant species diversity and community structure. (C) 2008 Elsevier B.V. All rights reserved.