Quantitative and structural characteristics of fallen woods in a secondary forest in Nanpan River basin
Fallen wood is an inevitable product during forest succession,which plays an important role in maintai-ning the stability,balance,and biodiversity of forest ecosystems.Many studies have explored the formation and de-composition process of fallen woods,but few referred to their quantity and structure.In this study,we investigated fallen woods in three plots with an area of 80 m×80 m,100 m×60 m and 80 m×70 m in a pine-oak mixed forest in the Nanpan River basin,Southwest China,.Fallen woods were divided into five grades(DCs-Ⅰ,DCs-Ⅱ,DCs-Ⅲ,DCs-Ⅳ and DCs-Ⅴ)according to their decay statuses.Species richness,abundance,and volume were esti-mated and the characteristics of spatial structure were analyzed with the stand spatial structure parameters(i.e.,uniform angle index,W;mingling,M;Dominance,U).Trees had many species,but with few individuals,which greatly contributed to volume.Shrubs had many individuals belonging to a few species,and accounted for a small part of volume.The abundance and volume of fallen woods increased directly or first increased and then decreased with increasing decay grades.Species markedly differed from each other in decay.Middle-and small-sized woods constituted the main body of fallen woods,and large-sized ones accounted for a small amount.On the whole,fallen woods were at a state of medium-low mixing(M=0.38-0.62)and slight aggregation(W=0.55-0.58),and had a balance of size differentiation(U=0.49-0.50).With the increases of decay grades,the size differentiation of fallen woods became large.These results clearly demonstrated the characteristics of species composition,quantity and spa-tial structure of fallen woods in a secondary forest in the Nanpan River basin,and indicated that the decay of fallen woods was closely related to species identity,their quantitative and spatial attributes,providing a basis for the sci-entific management of coarse woody debris.
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