| Vegetational restoration after disturbance, especially grave and accident disturbances, is an important issue for the restoration ecology to strengthen the study of disturbed vegetation after large scale and disaster disturbances. In this paper, we investigated the plant communities that restored naturally from different disturbance intensity during the 1976's earthquakes. The objectives of this study were to recognize fully about the species composition, structure and diversity for the disturbed communities, to analyze the relationship between the community diversity and the environmental factors, the relationship between the number and abundance of species, to make clear the biomass allocation in restoration communities, to find out how much effects the earthquake on radial growth of Abies faxoniana. The results can help us to know the speed of natural succession after the grave earthquake, and can explain clearly the main environmental factors which limited the regeneration of plant community, and provide scientific foundation and reference for the vegetation recovery after the 2008 Wenchuan earthquake. The brief results are as followings:1. Based on the investigated plots, quantitative classification and ordination were conducted by TWINSPAN and DCA method for the disturbed communities in the landslides triggered by Songpan-Pingwu earthquake. The plots were classified into three communities by methods of TWINSPAN and DCA, they are the community recovered from intensive earthquake disturbance (Community E), the community recovered from intermediate earthquake disturbance (Community T), and the community recovered from slightly disturbed forest community (Community F). The first axis of DCA indicated clearly the tendency from intensive to slight disturbance caused by earthquake. The results of ordination by DCA also showed the basic relationship between plant communities and environmental factors. The community E was positively related to the coverage of exposed rock surface, and negatively related to the moss cover, while the community F was negatively related to the coverage of exposed rock surface, and positively related to the moss cover.2.The species composition and diversity were studied for communities that restored naturally from different disturbance intensities during the 1976's earthquakes. Some main results are as followings:the community recovered from the Community E was characterized by the lack of tree layer, and the shrub and herb layers were dominated by heliophilous and pioneer species. The species composition of tree layer in the the community T was similar to the community F, except that the pioneer species were observed in the community T. The community T and F have no significant differences in species composition for shrub and herb layers. The numbers of family, genus and species in the community E were significant lower than in the community T and F, and there were no significant difference between community T and community F.3.The relationship between the plant diversity and the environmental factors were analyzed through the plant communities recovered from earthquake. The main results by a correlative analysis showed that the number of species, Shannon-wiener index and Simpson index were significantly negative related with the coverage of exposed rock surface, while the number of species and Shannon-wiener index were positive related with water contents of soil, organic matter of soil, thickness and coverage of moss. The main factors which impacted the biodiversity of the disturbed communities were the water content and soils.4. To analyze the relationship between species and abundance, the fitness of the neutral model to the restoration community was tested by using the woody and herbaceous plant data investigated in the plant communities that restored naturally from different disturbances during the 1976's earthquakes. It has been found that the species-abundance pattern in community E and F fitted well the neutral model, however, the species-abundance pattern in the community T did not fit the neutral model. It has been suggested that heterogeneity of habitat is the important factors that affect the fitness of the neutral model.5.Biomass is an important parameter in characterizing a forest ecological system. In order to understand fully the biomass allocation in restoration community, some models were used about woody biomass and the investigated data about herbaceous plant biomass and allocation in restoration communities. The main results showed that the aboveground biomass of pioneer woody plant in the community E and T was significant higher than in the community F, while the aboveground biomass of climax woody plant community E and T was significantly lower than in the community F. The aboveground biomass of different organs for woody plant from high to low were the trunk, the branch and the leaf. The aboveground biomass of the 3 communities were all higher than the underground. The aboveground of Fargesia denudate in the community T and the community F were significantly higher than in the community E, while there was no significant difference between the community T and the community F.6. Trees are very sensitivity to the environmental change. In the present study, it has been analyzed that the effects caused by the 1976's earthquake on residual Abies faxoniana and compared with Abies faxoniana of forests. The results showed that radial growth of residual Abies faxoniana in earthquake remains has an obvious increase in 1980 by moving t-test, while there was no significant change in forest, in other words, earthquake has a significant effect on residual Abies faxoniana growth. The contrastive analysis for the tree ring index between residual Abies faxoniana and forest Abies faxoniana also showed that the average tree ring index of residual Abies faxoniana in 1971～1975 was significantly lower than of forest Abies faxoniana, while it was significant higher than forest Abies faxoniana in 1981～1985. |
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