Growth process of Alnus japonica forest in Sengokubara basin, eastern Japan

Abstract

Alnus japonica is one of the representative species found in the riparian forests in Japan. However, excluding Hokkaido, currently not so many stands of A. japonica are in good condition. Since its habitat is wet and flat, large percentage of stands have been converted to rice fields. As such, our objective was to describe the growth process of individual A. japonica tree, changes of stand structure, forest floor vegetation and the dynamics of A. japonica forest in Sengokubara basin. This area is designated as a special protection area of Fuji-Hakone-Izu National Park. The number of individual trees had reduced gradually, while the canopy of the remaining trees had expanded to occupy the gaps in 28 years. The tall tree layer consisted of large number of A. japonica with a few Magnolia kobus 28 years ago. Since then, no other species have appeared, and no other individuals of A. japonica grew in tall tree layer during our observation period. Typically A. japonica is an early successional species, and seedlings cannot survive under the closed canopy. Due to the absence of young Alnus trees, possibilities prevail for dominant species to change following the disappearance of current forest.