Climatic trends, disturbances and short-term vegetation dynamics in a Mediterranean shrubland

Fire and erosion are two major disturbances affecting Mediterranean ecosyst ems. Both of them are closely related to climate. There is evidence of decr easing precipitation in the Mediterranean, particularly during summer. Ther e are also indications of an increased variability in the rainfall distribu tion. Climatic changes, though show high heterogeneity at a local scale. Ba sed on these observations, we have evaluated the following hypotheses for t he Region of Valencia (East Spain). (1) During the past three decades, clim atic conditions have become more favourable for wildfires and high erosivit y rainfall events. We have used 30-year climate records from 97 meteorologi cal stations to examine this. Results indicate that in general the hypothes is is true, although trends are spatially dependent. (2) The effect of high intensity rain on burned land may substantially affect short-term ecosyste m composition and function, and thus successional trajectories. Based on a plot scale study, we have assessed nutrient and vegetation dynamics after b urning a pyrophytic community dominated by gorse (Ulex parviflorus). Erosio n following high intensity rainfall affects physicochemical soil properties . As a consequence, plant cover is reduced and specific composition affecte d, changing the previous relationship between obligate seeder and resproute r species. (C) 2001 Elsevier Science B.V. All rights reserved.