Ecological Functions of Autumn Olives for Improving Vegetation Species Diversity and Habitat Conditions Supporting Their Growth: A Study of Tedorigawa River, Japan

ABSTRACT Thus far, no studies have quantitatively investigated the ecological functions of wood communities for increasing vegetation species diversity and promoting supportive habitat conditions for their growth. To fill this gap, this study investigates the ecological function of the autumn olive ( Elaeagnus umbellata var. umbellata ) community, a typical native wood community of Japan. We selected the Tedorigawa River, a representative rapid river of Japan, as a case‐study subject and conducted field surveys to investigate the relationships between the autumn olive, black locust, and oriental wormwood‐kawarahako communities (among six total vegetation communities) and their respective species compositions. Hydraulic simulations helped investigate significant differences in the cover ratio of native species that grow in rivers and alien species and, differences in the physical and environmental characteristics among the three typical vegetation communities in the river channel (native grass community, native wood community, and alien wood community). The results showed that autumn olives support the growth of native species that prefer wet conditions and control alien species' growth. This ecological function is supported by the characteristic hierarchical structure of autumn olives, including low‐density trunks and leaves and low height, which create bright light conditions in the community. The autumn olive community was also found to obstruct flood flow, which enhances the deposition of fine sediments and nutrients. These characteristics enhance wet conditions to support the growth of native species that prefer these conditions.