OFR and the FRG were once a single old-growth
forest. However, large parts of the forest were clear-cut
from the 1960s to the 1980s and converted into evergreen
conifer plantations, secondary forests, golf courses,
and agricultural lands (pastures and vegetable or
paddy fields), which now surround the two forests
(Fig. 1). OFR was preserved as an old-growth temperate
broad-leaved forest (Miyamoto and Sano 2008),
whereas the FRG remains as strips of forest ranging
from 5 to 200 m in width and 500 to 1500 m in length,
primarily along the river and ridges. Such deforestations,
followed by the establishment of evergreen conifer
plantations, have been a very common human activity
throughout Japan since the 1970s (Suzuki 2002). The
FRG is connected to the main forest by a small connecting
corridor, but since this corridor is very narrow
(a minimum of 2 m), it is unlikely that this corridor has
a substantial function in relation to bird dispersal.