抄録
Toward improving riparian forest management, we studied blowndown caused by Typhoon Songda in 2004 in riparian forests along the Ishikari River. Two kinds of riparian forests grow along this river: those within the embankments (“bankside forests” of predominantly Salix), and those in channel cutoffs outside the embankments (“cutoff forests” of predominantly Ulmus davidiana and Fraxinus mandshurica). Whereas blowdown in bankside forests was severe, blowdown in cutoff forests was minor. In bankside forests there was little damage to immature trees, but extensive branch and trunk breakage to mature trees (age‹20 years, H/D* ratio›85) and extensive uprooting to overmature trees (age‹30 years, H/D ratio›65). In cutoff forests there was little typhoon blowdown -even of mature trees -because the trees there are tall and thick enough to resist strong winds. Trees in the cutoff forests range in age from 60 to 190 years, and the H/D ratio for the trees of those ages ranges from 25 to 75. In view of windfall damage control, logging is needed every 20 years to maintain the bankside forests. However, if those forests are replanted with species found in the cutoff forests, then the logging can be greatly reduced in frequency -or possibly eliminated. Such replanting will also improve the discharge capacity and biodiversity. It is desirable to replant bankside forests with cutoff forest species.*height-diameter
