Fallen trees support river flow and aquatic habitats: The deep relationship between riparian forests and river organisms

by the Tohoku University Graduate School of Life Sciences
August 18, 2026

What kind of topography and water flow did Japan’s natural rivers originally have, and how did living things utilize those areas? A research group led by Associate Professor Hiromi Uno of Tohoku University, in collaboration with Professors Negishi and Kishida of Hokkaido University and the University of Tokyo, conducted a study using the Butokamabetsu River, which flows through the Uryu Research Forest of the Hokkaido University Northern Biosphere Field Science Center in northern Hokkaido, where a near-pristine mountain floodplain remains, as a model to link the topography and water flow of riparian forests and rivers with aquatic organisms.

As a result, they found 631 fallen trees along approximately 10 km of the river, and diverse water bodies such as stagnant pools and ponds were distributed in areas with many fallen trees. Many aquatic organisms mainly utilize the environment unique to floodplains, such as stagnant pools and ponds, and it was found that the complex river water flow shaped by fallen trees plays an important role in the coexistence of diverse aquatic organisms. Furthermore, it was revealed that even for adult char and huchen, which are found in the main river currents, the majority of juvenile fish actually utilize environments such as stagnant waters and ponds, demonstrating that complex water flow is essential for many organisms living in rivers.

It was found that riparian forests have not only direct effects such as providing hiding places, shade, and food sources for fish, but also indirect effects such as creating complex water flow by complicating the river’s topography, thereby providing habitats for diverse organisms. These results will serve as important foundational information for setting goals in natural restoration projects.

Keep reading (in Japanese): https://www.lifesci.tohoku.ac.jp/date/research/detail—id-53416.html

Read the Ecosphere paper: https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecs2.70700