IMPACTO DEL CAMBIO DE USO DEL SUELO E INCENDIOS EN LA ESTRUCTURA DE TRES COMUNIDADES FORESTALES

Abstract

The focus of this study was to evaluate the effect of land-use history and fires on forest structure in two mountain ranges of the southwestern United States of Northamerica (Animas Mountains) and northern Mexico (Sierra los Ajos). Three forest com'11unities in each mountain range were examined: (1) Pseudotsuga menziesii / Quercus gambelii found on northern aspects above 2,200 m; (2) Pinus strob,"formis / Pinus leiophylla I Pinus ponderosa found below 2,200 m, and (3) Pinus disco/ar/ Juniperus deppeana I Quercus sp. at elevations lower than 2000 m, bordering grasslands. Although size and age-class distributions far individual species were highly variable within a mountain range, they indicated that Pseudotsuga menziesii, Pinus strobiformis, and Pinus disco/ar are maintaining or increasing dominance in sorne stands in Animas Mountains, apparently as consequence of fire suppression and other land uses. In contrast, a less aggressive and usually less effective fire suppression policy in Sierra Los Ajos may have contributed to a continued dominance of the shade-intolerant Pinus ponderosa.