Control of snow cover duration in geomorphologic and biogeographic dynamics in Mediterranean mountains: Manzanares valley head, Sierra de Guadarrama (Spain)

摘要

This article examines the relationship between landforms, erosion, vegetal associations and yearly snow cover distribution and permanence. A study site was chosen near the source of the Manzanares River in the watersheds of two mountain streams, Condesa and Valdemartin, that merge at 1795 in altitude. The maximum altitude is Cabeza de Hierro Menor (2373 in, at 40 degrees 47' 56 '' N and 3 degrees 56' 10 '' W). The geomorphologic units, active erosion areas and vegetation associations were mapped. Weekly photographs of snow distribution were taken from 1996-2004 and provided data for snow cover mapping. ArcGis software was used for mapping and statistically comparisons of these data and the topographical data of the watersheds. The analyzes show that snow cover duration conditions the degree of erosive instability and phytoinstability, as indicated in simple correlation coefficients of 0.91 and 0.82, respectively. Furthermore, orientation (classified according to exposure to leeward winds) influences the amount of snow accumulation and is a determining factor in 70% of the snow cover duration. These findings were used to characterize and delimit the areas strongly influenced by lingering snow patches, and the results show that periods of >= 220 days/yr snow cover severely curtail growth in plant species with limited phytostabilizing capacity, and are associated with the acceleration of erosion processes.