BIODIVERSITY COMPONENTS AND CONSERVATION OF MEDITERRANEAN HEATHLANDS IN SOUTHERN SPAIN

Biodiversity is a complex issue which has frequently been extremely si mplified both by equating it with species richness, and by addressing it at the level of regional floras or faunas. In this paper we carry o ut a detailed assessment of biodiversity for conservation of Mediterra nean heathlands and related woodland understoreys on acidic 'islands' in the Gibraltar Strait region which are remarkable for their high spe cies richness, high endemism and low ratio of species per genus. The r elationship between the cover of woody plant species and environmental variables was studied by multivariate (DCCA) analysis of 30 samples. Species richness shows a unimodal relationship along the main environm ental gradient primarily determined by physiological tolerance to low pH and ecological competition. Quercus suber woodland understoreys und er intermediate environmental conditions are highest in species richne ss. Woody plant species are assigned to one of seven types of geograph ic ranges, and distributional spectra of community samples are represe nted. Open heathlands on nutrient-poor soils on mountain ridges are hi ghest in endemism. Species distinctness was estimated as the inverse o f the average number of species per genus ('taxonomic singularity') wi thin the Mediterranean Basin, Ibero-North African and Southwestern Spa in ranges. Quercus canariensis woodland understoreys on more fertile s oils on valley bottoms present the highest taxonomic singularity. The analysis at the community level of the three proposed biodiversity com ponents (species richness, endemism richness and taxonomic singularity ) is interpreted with the aim of formulating sound conservation strate gies of the communities examined. Although we use communities in the G ibraltar Strait area as a particular case study, we suggest that this methodology would help conservation efforts in other areas.