DEMOGRAPHIC TRAITS OF UNDERSTORY TREES AND POPULATION-DYNAMICS OF A PICEA-ABIES FOREST IN TAISETSUZAN NATIONAL-PARK, NORTHERN JAPAN

The size structure transition matrices of Picea jezoensis, Picea glehn ii and Abies sachalinensis of a sub-boreal forest in Hokkaido, norther n Japan were constructed based on the demography of each species (Fire d jezoensis and Picea glehnii were dealt with together as Picea) durin g a 4-year period. Two types of matrices, density-independent and dens ity-dependent population dynamics models, were investigated for evalua ting the 'waiting pattern' between Picea spp. and A. sachalinensis. Fo r the density-dependent model, it was assumed that the demographic tra its of understory trees, the recruitment rate, the understory mortalit y rate and the transition probability from the understory to canopy st ages, were regulated by the one-sided competitive effect of canopy tre es. The observed size structure of Fired was almost consistent with th e stationary size structure obtained in both the density-independent a nd the density-dependent models, whereas the observed size structure o f A. sachalinensis was not realized in the two models. The effects of both the transition probability from the understory to canopy stages a nd the recruitment rate on the dynamics of canopy trees were investiga ted. For Picea, two parameters - recruitment rate (e(i)) and transitio n probability from the understory to canopy stages-exponentially affec ted the dynamics of canopy trees. In contrast, for Abies sachalinensis , the two parameters affected linearly the dynamics of canopy trees. I n conclusion, the population dynamics of Picea and A. sachalinensis wa s determined by the parameters of the recruitment rate and the transit ion probability from the understory to canopy stages, relating to wait ing patterns of understory trees for future gap formation. In Picea, t he demographic parameters of understory trees intensively regulated th e dynamics of canopy trees if compared with A. sachalinensis, suggesti ng that the performance of understory trees plays a key role in the po pulation dynamics of Picea. This reflects the growth pattern of unders tory trees in the regeneration of the two species.