LIVESTOCK EFFECT ON FLORISTIC COMPOSITION AND VEGETATION STRUCTURE OF TWO DESERT SCRUBLANDS IN NORTHWEST COAHUILA, MEXICO

摘要

Microphyllous and rosetophyllous desert scrub plant communities dominate large parts of the state of Coahuila, Mexico, yet differences in how livestock grazing impacts these two plant communities are not well documented. In order to address this knowledge gap, we assessed livestock impact on plant species composition and vegetation structure in microphyllous and rosetophyllous desert scrublands in this northwestern Mexican state. We collected plant density, frequency, and cover data from sites with and without livestock grazing pressure that were otherwise similar in plant composition. We quantified intersite differences using the importance value index (IVI) and the Bray-Curtis similarity index. The species with the highest IVI for microphyllous scrubland were lechuguilla (Agave lechuguilla), honey mesquite (Prosopis glandulosa), and creosote bush (Larrea tridentata); however, in sites with presence of domestic herbivores, desert willow (Chilopsis linearis) and spiny hackberry (Celtis pallida) also showed high values. Plant species with the highest IVIs in rosetophyllous scrublands were lechuguilla, creosote bush, mariola (Parthenium incanum), and blue grama (Bouteloua gracilis) for both land use types. The Bray-Curtis similarity index between microphyllous desert scrub and rosetophyllous desert scrub was 62%. Moreover, microphyllous scrub with and without livestock had 48% similarity, whereas rosetophyllous scrub sites with and without livestock were 65% similar. Results indicate that livestock grazing significantly modifies plant species composition and vegetation structure in both types of the studied desert scrublands.