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

The increasing need for the risk assessment on 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. As well, there is an agreement in the northward migration of TC disturbance in Far East Asia in the future when meteorological changes accompanying with global warming are considered together. Therefore, this study assessed the canopy height damage by the historic typhoon Songda in 2004 in the perspective of the relations with topography, wind traits, and forest canopy types in northern Hokkaido, Japan. We found 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 leeward aspects. It was noted that canopy height damage of hardwood and mixed forests showed the threshold pattern at around 14 m in canopy height, whereas conifer was not the case. Strong causal relations were not observed between canopy damages (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 intermingled various 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 been rarely visited by typhoons but is projected to be more affected by increasing number of intense typhoons should be regarded as a high priority from this time forward for the sustainable forest management.