A measure for spatial heterogeneity of a grassland vegetation based on thebeta-binomial distribution

A method is proposed to estimate the frequency and the spatial heterogeneit y of occurrence of individual plant species composing the community of a gr assland or a plant community with a short height. The measure is based on t he beta-binomial distribution. The weighted average heterogeneity of all th e species composing a community provides a measure of community-level heter ogeneity determining the spatial intricateness of community composition of existing species. As an example to illustrate the method, a sown grassland with grazing cows was analysed, on 102 quadrats of 50 cm x 50 cm, each of w hich divided into four small quadrats of 25 cm x 25 cm. The frequency of oc currence for all the species was recorded in each small quadrat. Good fits to the beta-binomial series for most species of the community were obtained . These results indicate that (1) each species is distributed heterogeneous ly with respective spatial patterns, (2) the degree of heterogeneity is dif ferent from species to species, and (3) the beta-binomial distribution can be applied for grassland communities. Tn most of the observed species spati al heterogeneity is often characterized by species-specific propagating tra its: seed-propagating plant species exhibited a low heterogeneity/random pa ttern while clonal species exhibited a high heterogeneity/aggregated patter n. This measure can be applied to field surveys and to the estimation of co mmunity parameters for grassland diagnosis.