Effects of typhoons on leaf fall in hinoki cypress (Chamaecyparis obtusa Endlicher) plantations in Shikoku Island

摘要

Leaf fall was measured for 5 years (2002-2006) in adjacent thinned and unthinned plantations of hinoki cypress (Chamaecyparis obtusa Endlicher) at two different elevations in Kochi Prefecture, Shikoku Island, Japan. The region was hit by severe typhoons in 2004 and annual leaf fall in that year was1.17- 2.25 times greater than that in the pre-typhoon period (2002-2003). The effect of the typhoons on annual leaf-fall was greater at the higher elevation. At each elevation, the effect was greater in thethinned plots than in the unthinned plot. Post-typhoon annual leaf-fall (2005-2006) was1.05-1.41times greater than that in the pre-typhoon period (2002-2003). Although the impact of typhoons was greater in the thinned plots, the recovery of leaf litterwas not different between the tmnned and unthinned plots. The time of leaf fall in the typhoon year became earlier in forests at the higher elevation. At the lower elevation, leaf-fall duration increased in 2004 but the time of leaf fall did not change.The results indicate that susceptibility to strong winds is different between higher and lower elevations: greater leaf fall occurs immediately after strong winds at higher elevations, whereas leaves do not fall immediately after strong winds and damagedleaves fall gradually at lower elevations. These results suggest that the annual leaf fall can be recovered rapidly and that new leaf production may increase substantially after typhoon disturbance.