STRUCTURE AND DYNAMICS OF VEGETATION IN A CHILEAN ARID THORNSCRUB COMMUNITY

The structure and dynamics of vegetation in a Chilean arid thorn-scrub community within Parque Nacional Fray Jorge (30-degrees 38'S, 71-degr ees 40'W) were analyzed for a period of three years (1989-1991). These years differed markedly in annual precipitation; 1989 was a year of a verage rainfall (89 mm), 1990 was an extremely dry year (32 mm), and 1 991 was a comparatively wet year (233 mm). Rainfall had a noticeable e ffect on the cover of annual herbs, especially species that are restri cted to areas under bushes, but it had little effect on the cover of p erennial shrubs and herbs, except for the summer drought-deciduous spe cies. Shrub cover in the study site has remained about the same (60%) for almost 50 years.