TOWARDS GREATER UNIFORMITY OF SPECIES-DIVERSITY STUDIES IN MEDITERRANEAN-TYPE ECOSYSTEMS

Understanding of inter- and intra-continental patterns of plant specie s diversity in a variety of ecosystems has been hindered by several co nceptual and methodological shortcomings. In this paper two major area s of concern are identified and general guidelines for improving speci es diversity studies in Mediterranean-type ecosystems are suggested. A primary suggestion would be to standardize sampling techniques whenev er possible. An example would be to include progressive nesting of qua drats at various scales within a 0.1 ha sample plot. Plots should be a dequately stratified to represent the full range of environmental and disturbance gradients that occur within the overall study area. In add ition, each habitat and/or disturbance type should be adequately repli cated to ensure statistical validity of any comparisons undertaken. Sa mpling should take place during spring months when flowering and pheno logical activity is maximized. Secondly, greater uniformity in the ana lysis and presentation of diversity data would facilitate interstudy c omparisons. Use of the nested quadrat approach permits analysis of spe cies richness trends at scales ranging from 1 m2 to 1000 m2 or greater . Preference should be given to those diversity models and indices rec ognized as best depicting proportional abundances of species. In addit ion, identifying components of structural diversity contributed by var ious life- or growth-forms as well as native versus non-native element s would lead to fuller understanding of the data.