Non‐equilibrium dynamics of a wave‐regenerated forest subject to hierarchical disturbance

Questions How do strong windstorms affect the dynamics of a wave‐regenerated forest, long thought to be a shifting‐mosaic steady‐state system? Can large‐scale disturbance lead to non‐equilibrium dynamics in such a forest? Location A wave‐regenerated Abies forest in northern Yatsugatake, Japan. Methods We analysed the motion of a ‘regeneration wave’ using aerial photographs (1947–2012) and field surveys (1954–2012). Long‐term stand dynamics were surveyed along a transect established in 1954. Results The motion and structure of the regeneration waves indicated that the canopy was heavily disturbed by the typhoon in 1959. In 1954 (i.e. before the typhoon), the forest comprised stands of varying age based on a census along the transect. Older stands with high above‐ground biomass and high canopies disappeared after the typhoon. Consequently, the post‐typhoon forest mainly consisted of stands established around 1959. Thus, the typhoon caused a gradual change in age class distributions and in the above‐ground biomass of the forest. Species composition also varied considerably across census years, clearly indicating the influence of large‐scale disturbance. Conclusions The study forest changed drastically in structure after a major typhoon, and it continued to change during the subsequent 50 yr. The large‐scale disturbance clearly affected species composition, potentially contributing to the co‐existence of two Abies species. Our results suggest that, in combination, frequent small‐scale disturbance and infrequent large‐scale disturbance produce a non‐equilibrium state with respect to forest structure and species composition.