Julio Muñoz Jiménez

Plant colonization in Condesa nivation hollow, Sierra de Guadarrama (Spanish Central System).

Abstract. The purpose of this study was to determine plant distribution at a nivation hollow located in a Mediterranean high mountain area and to analyse the effects of snow cover, wind exposure, proximity to moisture and the characteristics of the substrate on the vegetation. We analyse these factors and interpret concurrent effects due to recent climate change. The nivation hollow, called Ventisquero de la Condesa, is located at 2258 m a.s.l., 40°47′10″N and 3°58′35″W, in the Sierra de Guadarrama (Madrid, Spain). We established 579 small sample plots in the study area, and grouped them into 29 transects where snow duration, wind exposure, availability of meltwater, geomorphologic instability and surface rockiness were examined directly and indirectly. The types of plants and the number of individuals per species were registered for each plot to establish ecological affinities among the 28 distinguishable species. Six showed the highest level of chionophily while nine showed the lowest adaptation to snow cover duration. A statistical study incorporating other variables applied in the research revealed that wind exposure, moisture capture and the intensity of geomorphologic dynamics have a highly significant correlation with nivation, while surface rockiness is a virtually independent factor. Due to environmental changes caused by recent global warming, several plant species, especially adapted to survival in snow conditions, coexist in the hollow with saxicolous plants that have invaded the site from adjacent grass and shrublands.

Transformaciones ambientales y paisajísticas en el borde occidental del área metropolitana de Ciudad de México.

La sierra de Las Cruces, Monte Alto y Monte Bajo, que, con direccion NW-SE, forma el limite occidental de la cuenca de Mexico, es un ambito geoecologicamente muy bien dotado y diversificado, que hasta hace algunas decadas pudo sostener una importante riqueza forestal. Sin embargo, desde mediados del siglo XX sus rampas de piedemonte y sus faldas orientales han sido alcanzadas por los suburbios de la Ciudad de Mexico, emplazandose de esta forma en ellas un acelerado proceso de ocupacion y cambio de usos. Como consecuencia de ello se han ocasionado grandes alteraciones e impactos en el medio fisico, que se traducen en evidentes modificaciones de la configuracion paisajistica de la montana