The leaves of this forest used to fall into the water and become mulch, protecting the stream. The fish eat insects which come to feed on and break down the fallen leaves, so that the presence of the trees insures a plentiful food supply for the salmon. Moreover, the brook masu salmon does best in water which is "clear but not too clear, muddy but not too muddy."
溪流兩岸的闊葉樹林，落葉掉落水面後，化作春泥更護溪，櫻花鉤吻鮭的食物﹘﹘石蠶等水生昆蟲會簇擁而來分解枯枝落葉，魚兒食物也就不虞匱乏。