Modelling stem breakage caused by typhoons in plantation Cryptomeria japonica forests

Typhoon damaged plantation sugi (Cryptomeria japonica D. Don) forests were studied to mechanistically understand the stem breakage in relation to stand structure. In the study sites where most trees had been blown down, the tree dimensions of tree height, diameter at breast height, height and diameter at the point of stem breakage were measured for all trees in the plots. An expanded allometric relationship of tree height over DBH and a constant height to crown base for each tree were found at each site. Employing the Sawada model to simulate physical stresses in tree stems caused by outside forces, the predicted heights of maximum compression stress exhibited good agreement with the actual heights of stem breakage. It was suggested, however, from the distribution of the bending stress in a stem, that the height of stem breakage may oscillate around the predictions due to physical defects in wood, and that compression failure may occur along the stem even for the standing trees which survived the typhoon. The present simulation model can well describe the effects of tree form which directly affect the height at stem breakage. (C) 2000 Elsevier Science B.V. All rights reserved.