| Tsuga longibracteata is the rare specie of China , which is precious andendangering because of destroy and difficult regeneration. So it had been classified as protecting plant in the second class. The scientific cognition for community structure and discipline of dynamic regeneration is the pivotal thing for continuance keeping of Tsuga longibracteata. The study of forest gaps is very important for natural regeneration and dynamic changes of Tsuga longibracteata community.Forming characteristics of gaps among the Tsuga longibracteata forest were preliminarily studied through the size distribution of gaps, gap-forming manner and the characteristics of gap makers in the essay. The results showed that for the quantity percentage, the size of canopy gap(CG) and that of expanded gap(EG) centralized at 50~100 m2 and 100~300m2, respectively, and the percentage were 42.62% and 34.43% respectively; for the quantity percentage, the size of canopy gap(CG) and that of expanded gap(EG) centralized at 150~200m2 and 200~300m2, respectively, and the percentage were 34.15% and 33.97% respectively. The ratio of the CG area vs the EG area centralized at 0.2-0.4.The main manners of gap formation in the forest were standing death and stem breakage at trunk, which percentage are 54.11% and 34.25%, respectively. Most of the gaps in the forest were formed by 2 gap makers, and the percentage is 36.07%, averaging 2.39 trees per gap. The area of EG and CG formed by one gap maker were 85.43 m2 and 12.61 m2 , respectively. Most of gap makers are Tsuga longibracteata, Castanopsis carlesii, Cyclobalanopsis myrsinaefolia, Rhododendron simiarum, Michelia maudiae, Castanopsis reyri, Schima superba, Cunninghamia lanceolata and pinus massoniana, and of which most are Tsuga longibracteata, and it is most possible for them to create gaps in the manner of tree-fall or standing death when they are 20-40 cm in D.B.H. and >20 m in height. The percentage of gaps at Prophase, Metaphase and Anaphase are 21.31%. 45.54% and 31.15%, respectively.The species diversity and community stability of gaps and non-gaps in Tsuga longibracteata were studied by using Margalef richness index (R), Shannon-Wiener index (H), Pielou evenness index (E), evenness-dominance-abundance index (Z),ecological dominance( ), community dominance(C) and Zheng yuanrun's M.Godron method. The results showed that the R, H and E calculated by individuals numbers in gaps are 16.16,3.86 and 0.71, respectively, which were higher than that of non-gaps, which wree:7.33,3.46 and 0.88 .respectively. The H and Z calculated by importance value of gaps were also higher than that of non-gaps. While the and C of gaps were lower than that of non-gaps. It suggested that species diversity of the community increased and stabilitydecreased due to the existence of gaps formed by natural disturbance. The results of community stability caculated by M method are accord with this. The whole forest community is in typical metastability state.Simpson diversity index (D), Shannon-Wiener diversity index (H) and Pielou evenness index (E) were used to calculate a diversity in gap gradient .While the Sorenson index, Bray-Curtis and Moristia-Horn index were used to study P diversity. The results showed that species a diversity of the arbor layer and shrub layer gradually decreased from gap centre to the non-gap area, and the species evenness was high on edges and low in the center. The least P diversity of arbor layer was appeared at area from near center to expanded gap, and the P diversity was gradually increased in transition area from gap center to near center.expanded gap to gap border and gap border to non-gap, While the least B diversity of shrub layer was at area from gap center to near center, and the other three transition areas had no great difference. Six aggregate indices(C,I, 1, M*,PAI, k) were used to analyse spatial distribution pattern of Tsuga longibracteata seedling in gaps of different develop phase and different size. The results showed that the seedling were clumped in early phase gaps and... |
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