Spatiotemporal Dynamic IVlodels of Plant Populations and Communities

TCre idea of relating spatial patterns and temporal processes in plant community dynamics is not new, 6ut its transform-ation into realistic spatiotemporal models is the result of quite recent methodological developments. There are now two classes of analytical model and a broad class of simulation models pertaining to the role of spatial structure in vegetation dynamics. They indicate that any community-dynamical theory intended to be predictive should not omit the spatial aspects of plant population dynamics, Gecause these may radically change the conditions of persist-ence and coexistence. The sedentary nature of higher plants has important consequences for vegetation dynamics, for at least two obvious reasons. First, a sessile organism has no chance to change its own environment by simply moving away from temporarily un-favorable habitats; second, it has no contact with individuals outside a limited area of its neighbourhood-that is, the interaction of an in-dividual with others is always local’. These spatial aspects are not in-cluded in the assumptions of the many different versions of classi-cal Lotka-Volterra mode1s2J, which are often conceptual and formal analogues of the kinetic equations of homogeneous chemical reac-tions. At the moment, there are three major, biologically more-inclusive classes of population-dynamics model that do not entail spatial mixing of popu-lations and overall environmental homogeneity, namely: ( I) reaction-diffusion models; (2) island or patchy-environment models; and (3) neighbourhood models. All three types of spatiotemporal model, when applied to vegetation dynamics, address the same prob-lem in a broad sense, namely the spatial aspects and conditions of either the persistence of a single population, or the coexistence o