Surviving States of Primary Trees in Residual Areas Seven Years after Strip Clear-cutting in a Natural Laurel Forest in Okinawa, Japan

摘要

The effect of strip clear-cutting on surviving states of the primary trees 7 years post-cut in a subtropical laurel forest in Okinawa was studied. In the 3,600 m~2 study area, six permanent plots named A to F were established by sequence in January 1995. A tree census was conducted; all trees with height equal to or higher than 1.2 m in the study plots were numbered and recorded with species name, height, and diameter at breast height (DBH). Strip clear-cutting was conducted after the tree census inFebruary; the trees in plots A, C, E were clear-felled at the base at 20 cm height above the ground, versus the other trees in plots B, D and F, which remained. In the present study, a new tree census was performed in December 2002. The primary trees consisted of 51 tree species 550 tree stems in plots B, D and F were checked. Examined and measures were the surviving state, DBH and height. The current state of the primary trees was divided into seven types. The results showed the majority of stems (64.7) remained in regular state without obvious damage, while 35.3 of them were in disturbance, i.e. 15.8 of them were dead, 12.9 of them were living in standing state with breakdown at treetop or with withered tops, and 6.6 of them were living in falling state. The surviving states of primary trees differed by DBHs, life forms and tree species. The smallest DBH group (1-2 cm) had the highest mortality rate, versus the big DBH group (>12 cm) which had the highest rate of breakdown at treetop. Ardisiaquinquegona, a kind of nanophanerophyte species, had the majority of the dead stems, while the dominant species, Castanopsis sieboldii, had the low mortality (6.3), with most stems (71.9) in regular state.