AN ISOZYME STUDY OF CLONE DIVERSITY AND RELATIVE IMPORTANCE OF SEXUALAND VEGETATIVE RECRUITMENT IN THE GRASS BRACHYPODIUM-PINNATUM

We asked whether differences in abundance and seed production of Brach ypodium pinnatum after 16 yr of four different experimental land use r egimes were reflected in differences in vegetative dispersal distance, clone diversity, clone area, and the proportions of sexual and vegeta tive recruitment. Mean vegetative dispersal distance was 5.5 mm yr(-1) . Electrophoresis of 5 polymorphic isozyme loci of 20 tillers sampled at defined positions in each of twelve 1 x 6 m sampling areas (3 per t reatment) revealed considerable clonal diversity. Per sampling area we found on avarage 9.98 enzyme phenotypes (clones), mean Simpson index was 0.825, and mean Shannon index 0.801. The mean ratio of sexual vs v egetative recruitment was about 1:32 000. Despite this low ratio, clon al diversity within the population of B. pinnatum was higher than repo rted for other clonal plant populations, possibly because of its high ramet densities. Mean clone area was 5.73 m(2), i.e. mean clone radius was 1.35 m. None of the 10 pairwise correlations between abundance an d seed production on the one hand, and number of clones per plot sampl e, plot Simpson index, plot Shannon index, ratio of vegetative vs sexu al recruitment, and clone area on the other, was significant. Mean clo ne radius was 245 times larger than the mean distance of yearly vegeta tive dispersal which suggests old ages and low turnover rates of clone s. The time scale of the inert response of clonal diversity of B. pinn atum to changes in land use appears to largely exceed the experimental period of 16 yr.