Jinyun Subtropical Evergreen Broad-leaved Forest Gap Dynamics

1. Forming characteristics of gap among the subtropical evergreen broad-leaved forest in Jinyun Mountain were preliminarily studied through the gap-forming manner, size distribution of gap and the characteristics of gap maker in the essay. The results show that the main manners of gap formation in the forest are uprooting, stem breakage and standing death. Most of the gaps in the forest were formed by 2 or 3 gap makers, averaging 2.88 trees per gap. The size of expanded gap (EG) and that of canopy gap (CG) centralize at 100～300 m2 and <150 m2, respectively; the ratio of the EG diameter vs. the gap height and that of the CG diameter vs. the gap height centralize at 0.6～1.4 and 0.2～0.8,respectively.Most of the gap makers are Pinus massoniana, Symplocos setchuanensis, Gordonia acuminata, Schima argentea, Engelhardtia roxburghiana and Castanopsis carlesii var. spinulosa, and it is most possible for them to creat gaps in the manner of tree-fall or standing death when they are 20～50 cm in D.B.H. and 15～25 in in height. The area of EG and CG formed by one gap maker average 76.8 m2 and 34.4m2, respectively. 2. The species diversity and community stability of the gap and non-gap stands in Jinyun Mountain were studied by using species richness index (dGL), Shannon-Weiner index (H), Pielou evenness index(J),Simpson index(D),ecological dominance( A), evenness-dominance-abundance index(Z) and community dominance (C).The results show that the dGL,H?J and D calculated by individuals numbers in gap are 12.14,4.62, O.70,13.32,respectively. The shrub layer plays agreater role than other layers. Indices of species diversity in non-gap stand are 6.32, 3.74,0.66 and 8.16, respectively, which are lower than that in gap, obviously. Evenness-dominance- abundance index (Z) of the plant community in gap was far higher than that in non-gap stand. However, ecological dominance and community dominance in gap are smaller than those in non- gap stand significantly. It suggests that species diversity of the community increases and community stability decreases due to the existence of gap formed by natural or man-made disturbance. The whole forest community is in typical metastability state. 3. The gap-phase trees replacement was studied in a secondary conifer-broad-leaved mixed forest distributed densely in Jinyun Mountain, Chongqing. And the succession tendency of gaps in the type of forest was predicted. The results show that the pious massoniana population performs intensively reciprocal replacement pattern. Gordonia acuminata , Symplocos setchuanensis and the other evergreen broad-leaved tree species display both self replacement and reciprocal replacement patterns. The current trees replacement process in gaps does not act to maintain the current community composition. The analysis of Markov transition martrix shows that the pious massoniana population will lose its predominant position in the future composition of the forest canopy. The whole community is in the succession process from the conifer-broadleaved mixed forest to the evergreen broad-leaved forest.