Question: How do wind and snow disturbances affect the successional replacement of Picea glehnii by Abies sachalinensis in a sub-alpine coniferous forest?

Location: Cool temperate, northern Japan.

Methods: Tree demography (growth, mortality and recruitment rates) was determined by repeated measurements of stem diameter and height, and multiple censuses in four Picea-Abies stands undergoing succession. Above-ground stand biomass, residence time and tree growth trajectories of the component species were estimated to examine successional changes in structure and dynamics. Individual based simulations were used to examine the effects of disturbances that slowed down succession. Multiple regression analyses were used to determine the relative importance of disturbance frequency and intensity on species composition during succession.

Results: Above-ground biomass was larger in P. glehnii than in A. sachalinensis stands, whereas residence time, a proxy of productivity, was much shorter for A. sachalinensis than for P. glehnii populations. During successional replacement, both species increased in initial growth rate and decreased in size-dependency of growth in canopy gaps. These plastic growth responses were more prominent in P. glehnii than in A. sachalinensis. Disturbance frequency was the most important predictor of species composition in the simulations, and wind-storms were more important than snowfall in terms of disturbance intensity.

Conclusions: The frequency of natural disturbances does not have the potential to initiate stand dynamics but it does, however, slow down succession. When disturbance is locally frequent because of the direction and pitch of the topography, early-successional P. glehnii stands may persist for thousands of years.

Abbreviations: AS = Abies sachalinensis; PG = Picea glehnii; RGR = Relative growth rate.

Nomenclature: Hayashi et al. (1985).