The Effects Of Human Disturbance On Characteristics Of Woody Debris Of Subtropical Forests In Gutian Mountain

Woody debris is one of important componets of forest ecosystem, and play great roles in the structure and functioning of forest ecosystems. Currently, most of forests have been degraded into secondary or plantation forest under severe human disturbances. With global climate change and rapid extinction of biodiversity, it is worthwhile to evaluate the effect of human disturbance on the woody debris of forest ecosystem, for effective conservation of biodiversity and understanding the response of different forest ecosystems to climate change.This study investigated the woody debris in the four types of subtropical forests with different human disturbances:plantation forest (PL), secondary forest suffering from human disturbance twice (S2), secondary forest suffering from human disturbance once (S1) and primary forest (PR). Long-transect and quadrat sampling were used in this study. The objective was to look into the effect of human disturbance on the components, structure, storage of woody debris in forest ecosystems, and the correlation of this effect with environmental variables. The main results were as follow:(1) The fine woody debris mainly consisted of standing dead trees in the forests PL and S2, while fallen dead trees in the forest S1and PR. The mass of fine woody debris decreased with human disturbance from20.199(PR),15.67(S1),4.049(S2) to1.342t/ha (PL), and the volume decreased as well from40.956(PR),36.657(S1),12.568(S2) to5.415m3/ha (PL). The coarse woody debris mainly consisted of fallen dead trees in the forest PR, S1and PL, with decrease in the mass from12.383,15.506to0.774t/ha, and in the volume from33.98,46.182to4.705m3/ha. However, the stump dominated the coarse woody debris in the forest S2. (2) The woody debris differed in their diameter structure among different forests. The majority of fine woody debirs was between2and10cm in diameter in the forest PL and S2, mainly as a result of standing dead trees, accounting for94and76%of the mass of total fine woody debirs, and96and73%of the volume. By contrast, majority of fine woody debris was between5and20cm in diameter in the forest PR and S1, accounting for82and87%of the mass of total fine woody debris, and81and85%of the volume, and mainly resulting from fallen dead trees. The coarse woody debris were dominant in diameter between40and50cm for the forest PL and S2, accounting for43and92%of the mass of total coarse woody debris; while between20and30cm for the forest PR and S1, accounting for78and67%of total coarse woody debris mass. The mass of large coarse woody debris (40-50cm in diameter) declined with human disturbance from2.218(PR),0.163(S1),0.308(S2) to0.342t/ha (PL); the corresponding volume decreased as well from6.661,0.415,0.081to2.251m3/ha.(3) The woody debris differed in decaying degree among different forests. The most of fine woody debris were less decayed and at the class1, thus presented half U-shape, to which standing dead trees contributed a lot. By contrast, the most of fine woody debris more decayed and at class2in the forest PR and S1, and exhibited a reverse U-shape, to which fallen dead trees contributed a lot. The coarse woody debris showed a decrease in the mass and volume of well-decayed debris with human disturbance. For the class4, the mass and volume of woody debris were0.451t/ha and1.152m3/ha in the primary forest, while were zero in the other forests. For the class5, the mass of woody debris was0.423,0and0.002t/ha for the forest PR, S1and S2respectively, and the corresponding volume was1.090,0and0.009m3/ha.(4) The woody debris also differed in species composition among different forests. The woody debris was dominated by Cunninghamia lanceolata in the plantation forest, by Castanopsis carlesii, Castanopsis eyrei&Pinus massoniana in the forest S2, by Pinus massoniana&Castanopsis carlesii in the forest S1, and by Castanopsis eyrei&Schima superba etc. in the primary forest.(5) In the four types of forests, the mass of woody debris was larger at lower elevations and slopes. In the plantation forest and two types of secondary forests, the mass of woody debris was larger on the south-facing slope than on the north-facing slope. However, in the primary forest, the woody debris mass was greater on the north-facing slopes.