MODELS OF FOREST DYNAMICS BASED ON ROLES OF TREE SPECIES

A linkage between the two major modeling approaches to forest dynamics , transition Markovian models and JABOWA-FORET type simulators, is gen erated by developing a compact model of forest dynamics. This patch tr ansition model utilizes functional roles instead of species. The roles or types are based on the regeneration and mortality characteristics of tree species; specifically, the requirements of canopy gaps for reg eneration and the capacity to create canopy gaps upon death. A gap-siz e plot can be assigned to each of a set of states defined according to dominance of one of the roles. Transition probabilities among these s tates and mean holding times in each transition lead to semi-Markovian analytical calculations of the stationary state probabilities. Forest dynamics, as the proportions of total canopy space occupied by each r ole in a collection of gap-size plots, can be analyzed and simulated u sing a chain of first-order differential equations to emulate the dist ributed time-delays. Additional fixed time-delays in the transition of every pair of states is also included to account for long latencies. In addition to simplifying the simulations, the resulting model can al so utilize available results of the theory of semi-Markov processes; a nd therefore, can provide analytical guidance to the simulations, the feasibility of direct exploration of hypothesis and the possibility of fast computation from closed-form solutions and formulae. These advan tages can especially be useful in the simulation of landscape dynamics and species-rich tropical forests.