Abstract

Principles of vegetation dynamic modelling in the successional time scale are discussed. Global models of biosphere predict shifts of bioclimatic zones in response to climate changes by means of corresponding shifts in global space of climatic indices designed in a special way. On the contrary, The localization principle lays a local geobotanic knowledge into the foundation of the models, namely, the knowledge of conceptual scheme for, and regularities in those plant succession which proceed in the area under study. The Markov-property principle (postulate) arises once a particular scheme of succession is determined, thereafter random Markov chains serve a convenient tool to describe in formal terms how phytocoenoses change in time. The ergodicity principle (hypothesis) is used whenever the behaviour of a temporal (successional) series is judged from the analogy with that of the spatial (ecological) one or vice versa, and this kind of reasoning is generalized in the fundamental mathematical notion of ergodicity. The homogeneity principle, i.e. independence of time in the transition probabilities of the chain, gives rise to a mathematical property in common of such models, namely, convergence to a stable limit distribution, thus meeting the major paradigm of succession theory: regular movement from pioneer stages to the stable (poly) climax one. However traditional time-homogeneous models (with constant transition probabilities) accept actually the hypothesis environmental invariance, which can hardly be accepted when the matter is about long-term prediction in the successional time scale. Models of new generation, the inhomogeneous chains, in which the transition probabilities are designed as functions of key factors of environment influencing the course of succession, now loose the algebraic elegance of their homogeneous prototypes but gain sensivity to real (climatic, in particular) parameters of the environment. The problem to model successions under global changes is thus reduced to the task to scale the global climate scenario down to the level of local key factors. In the gnosiological perspective, these models signify a move from phenomenology to the causality principle, which the homogeneous description has been a priori ruling out. The theoretical principles are exemplified with a practice in modelling successions in forest-steppe zone.