Altitudinal patterns of plant diversity, cover, and life forms in a warm arid mountain: Insights from Sierra de Velasco, Argentina

Abstract

Mountains are important reservoirs ofbiodiversity and endemism on a global scale, but littleis known about the altitudinal configuration of thisdiversity and its driving factors in arid mountains. Weexplored variations in composition, diversity, cover,and life forms of vascular plants along a completealtitudinal gradient (1300-4000 m a.s.l) in Sierra deVelasco, an arid mountain in northwestern Argentina.We evaluated the influence of environmental variableson plant diversity and cover. Field sampling wasconducted in the northern sector of the Sa. de Velasco,on the western slope in eight 50 m wide altitudinalbands at 400 m elevation intervals. We usedrectangular plots (20 x 4 m; n:10/altitudinal band) toregister the vascular plants of all the growth forms, andlinear transects (20 m long.; n:30/altitudinal band) toquantify the vegetation cover using the point interceptmethod. Diversity was calculated using hill numbers.Data analysis included non-metric multidimensionalscaling (NMDS), indicator species analysis,generalized linear models (GLMs), and variancepartitioning analysis. A total of 232 species from 51families and 158 genera were registered. Speciescomposition showed greater similarity at intermediateelevations. Plant diversity and cover exhibited aunimodal distribution, peaking at intermediateelevations (2100-2500 m). In contrast, life forms´distribution showed divergent patterns. Therophytesand succulents predominated at low altitudes,phanerophytes and hemicryptophytes at mediumaltitudes, and chamaephytes and geophytes at highaltitudes. The altitudinal patterns of plant diversityand cover were primarily driven by climatic factors.Conservation efforts in the Sierra de Velasco shouldfocus on the middle and upper zones due to their highbiodiversity and vulnerability to climate change.