TRANSITION AND GAP MODELS OF FOREST DYNAMICS

We describe and apply a correspondence between two major modeling appr oaches to forest dynamics: transition markovian models and Sap models or JABOWA-FORET type simulators. A transition model can be derived fro m a gap model by defining states on the basis of species, functional r oles, vertical structure, or other convenient cover types. A gap-size plot can be assigned to one state according to dominance of one of the se cover types. A semi-Markov framework is used for the transition mod el by considering not only the transition probabilities among the stat es, but also the holding times in each transition. The holding times a re considered to be a combination of distributed and fixed time delays . Spatial extensions are possible by considering collections of gap-si ze plots and the. proportions of these plots occupied by each state. T he advantages of this approach include: reducing simulation time, anal ytical guidance to the simulations, direct analytical exploration of h ypothesis and the possibility of fast computation from closed-form sol utions and formulae. These advantages can be useful in the simulation of landscape dynamics and of species-rich forests, as well as in desig ning management strategies. A preliminary application to the H. J. And rews forest in the Oregon Cascades is presented for demonstration.