Canopy height damage by Typhoon Songda in Northern Hokkaido, Japan, in 2004

Abstract The increasing need for the risk assessment of disastrous wind disturbance, especially by tropical cyclones (TCs), has been emphasized because the number of intense TCs is projected to increase due to global warming, though there are some discrepancies across oceanic basins. There is also an agreement of the northward migration of TC disturbance in Far East Asia in the future, when meteorological changes accompanying global warming are considered together. This study assessed the canopy height damage caused by the historic Typhoon Songda in 2004 from the perspective of the relations with topography, wind traits, and forest canopy types in northern Hokkaido, Japan. We found that the order of canopy height damage was consistent along every single aspect and every canopy height class with conifer-canopied forest > mixed-canopied forest > hardwood-canopied forest and higher damage on windward aspects than on leeward aspects. It was noted that the canopy height damage to hardwood and mixed forests showed a threshold pattern at around 14 m in canopy height, whereas for conifer forests, this was not the case. Strong causal relations were not observed between canopy damage (outcomes) and wind severity, inclination of slope, or canopy height (causes), though the causal relations were highly significant between wind severity or canopy height (mediators) and altitude or inclination of slope (causes) for all the studied canopy types. Given typhoon-induced forest damage is the consequence of the interactions among various intermingled biotic and abiotic causes and that areas affected by intense typhoons are anticipated to extend northward, more case studies in regions such as Hokkaido in Japan and the further north, which have rarely been visited by typhoons but are projected to be more affected by increasing number of intense typhoons, should be regarded as a high priority from this time forward for sustainable forest management.