Species richness in relation to phosphorus and competition in a Mediterranean dwarf-shrub community

Changes in species richness and productivity in a Mediterranean dwarf-shrub community were documented during 5 years following treatments intended to improve soil fertility and reduce shrub cover. Five treatments, replicated five times, were tested: (a) shrub cover reduction by selective herbicide application; (b) application of medium levels of phosphorus; (c) application of high doses of phosphorus; (d) a combined herbicide and phosphorus application; (e) an untreated control. Species were classified into nine functional groups according to life cycle, growth form and taxonomy: trees, shrubs, climbers, geophytes, perennial and annual grasses, annual legumes, perennial and annual forbs. The perennial and annual grasses, climbers, perennial forbs and geophytes showed no significant response to any treatment. Phosphorus application significantly increased the productivity and the richness of annual legume species, while herbicide treatment significantly reduced the frequency and richness of shrubs and increased those of annual forbs. Greater biomass production did not lead to a decrease in species richness; on the contrary, it was positively related to greater species richness, especially of the legume component.