Sustainability of an isolated beech-dwarf bamboo stand: analysis of forest dynamics with individual based model

The beech Fagus crenata forest on Mt. Jippo in southwestern Japan has been reduced to small fragments by past human activity. The forest floor is covered by dense dwarf-bamboo, Sasa, which is an inhibitor of beech regeneration. One of the ecological features of Sasa is that it withers synchronously over a large area once every several decades. An individual based model (IBM) was developed to evaluate the sustainability of such a fragmented beech stand considering the dynamics of Sasa. The model has three submodels for beech individuals: growth, mortality and seed production. The parameters of these submodels are estimated from field measurements. By using this model together with Sasa dynamics, we can evaluate the adverse effect of Sasa on enhancing the risk of extinction of a single fragmented beech stand over 500 years. The results obtained by Monte Carlo simulations are: (1) Sasa has a strong impact on the sustainability of a isolated beech stand; (2) the effects of two parameters for Sasa life history, the longevity and the recovery time, can be statistically separated from each other; and (3) the probability of extinction of a beech stand depends much more strongly on the parameters of beech mortality than those of growth rate.