Forest Structure and Maintenance Mechanisms of Montane Riparian Forests Under Extreme Snowfall in the Cool‐Temperate Zone of Western Fukushima, Japan

ABSTRACT To clarify the characteristics of montane riparian forests in extreme snowfall areas, the community composition, forest structure, and growth of dominant tree species in dwarf montane riparian forests, established in extreme snowfall environments (maximum snow depth of 5 m), were compared with those of tall‐tree montane riparian forests in heavy snowfall environments (maximum snow depth of 2 m) in the Tadami region of Japan. The dominant species in both forests were high‐sprouting Pterocarya rhoifolia and low‐sprouting Aesculus turbinata , which are representative of Japan's cool‐temperate montane riparian forests. In the tall‐tree montane riparian forest, both species exhibited single‐trunk forms with a maximum height of about 30 m, whereas in the dwarf montane riparian forest, P. rhoifolia had a maximum bent trunk length of about 18 m and a height of 10 m, and produced more and smaller sprout trunks, which appeared to contribute to stool persistence, whereas A. turbinata produced a single trunk in creeping form, with a maximum trunk length of 30 m and a height of about 5 m. Thus, although P. rhoifolia and A. turbinata were dominant in forests with both heavy and extreme snowfall, they had different survival strategies in terms of sprouting, dwarfing, and layering in response to extreme snowfall. In dwarf riparian forests, Acer nipponicum , which is common in heavier snow environments, dominated after P. rhoifolia and A. turbinata . These findings suggest that montane riparian forests under extreme snow conditions are maintained by tree species that are adapted to severe snow accumulation.