Clonal plant species in a dry-grassland community: A simulation study of long-term population dynamics

An individual-based spatially explicit grid-based model is developed to simulate the simultaneous development of two clonally growing grassland plant species. The model is based on long-term permanent-plot observations in a low-cover Thymo-Festucetum grassland community which is characterized, besides of some low-abundant ('sparse') species, by the interaction between the perennial tuft grass Festuca cinerea and the stoloniferous rosette plant Hieracium pilosella. The grid-based model includes rules for seedling recruitment, diaspore exchange, mortality, tuft growth and rosette establishment, local interactions, and considers the dependence of population parameters on environmental factors (weather). The simulations give the characteristic spatial features of the community (aggregations of grass tufts and of rosettes) and the highly fluctuating species abundances, They allow the assessment of the importance of different factors which control the abundances in the community: reproduction modes, intra- and interspecific interactions, dependence of life-history processes on weather conditions, and overall climatic conditions. The mechanisms of the spatially explicit model are concentrated by averaging over local interactions into analytical models (stochastic difference equations) which form a basis for a general insight into community dynamics and for a large-scale study of heterogeneous grassland communities containing clonal plant species. (C) 1997 Elsevier Science B.V.