Dynamics of plant community traits during an 18-year natural restoration in the degraded sandy grassland of Hunshandak Sandland
Notice bibliographique
Résumé
One of the four largest sandlands in China, Hunshandak Sandland was once the flourish grassland, but now it is different, with shifting sand dune accounting for 50 % of the whole area. The percentage of shifting sand dune is 20 folds of that 50 years ago. Strong winds, occurring always in the winter and spring with an average speed of 4～5 m/s and the strongest 30 m/s, greatly intensify the degradation. Local people's survival has been threatened largely by sandland degradation. More seriously, heave windy storms threaten the ecological environments of Beijing and Tianjin owing to long-trem transportation of dust materials. So, it is an urgent task to restore the degraded ecosystems for the purpose of both ecological security and the survivals of local societies. It is well known that the law of vegetation succession should be well understood before any restoration measures to be conducted. Therefore, in this study, we investigated various aspects of plant community, e.g., the species richness, life form diversity and functional diversity. We designed our experiment through using the space series to replace time courses in degraded areas of Hunshandak Sandland which have been enclosed for 18 years (1985～2003). By doing so, was analyzed the relationship between restoration times and species diversity, above ground biomass, and community coverage, etc. The number of species, biomass and community coverage greatly increased at first stage, then maintained steady or decreased slightly along the 18-year restoration courses. Thirty-one species were recorded in all quadrats, among which 3 species occurred in shifting sand dunes and 21 species in fixed sand dunes. Based on the community characteristics, the restoration processes can be divided into 3 stages: (1) During the first two years of enclosing, the species richness increased 2 fold, from the 3 species to 6 species. Community coverage increased by 6 fold, while the species diversity increased slowly during this stage. Such stage could be regarded as a turn from shifting sand dune to semi-fixation sand dune. (2) From the 3~(rd) year to the 5~(th) year of enclosing, species richness and diversity greatly increased in spite of the coverage grew up slightly. The number of species increases from 6 to 21, suggesting a key process for succession restoration as indicated by the quick increase of species diversity. This could be considered as a turn from semi-fixation sand dunes to fixation sand dunes. (3) After the 6~(th) year of enclosing, the species diversity, species richness and community coverage maintained steady status or slight decrease. Such a result announces the community restoration has been successful. As far as the functional type are concerned, C_3 and C_4 plant occurred in the whole process of natural restoration. C_4 plant played an important role in the early stage, while the join of more C_3 species were necessary in stabilizing the community in the late stage. Legume species might be vital to the improvement of soil nutrients although they took up a small proportion in plant community. For life forms, annual plants predominated during the early stage, while the woody species dominated in the late stage of succession. This might indicate that the woody plant is vital in fixing the sand dunes. Generally, species diversity, coverage and aboveground biomass increased firstly, then maintain steady or decrease gently, with the correlations being a shape of parabola (P0.001). The specie diversity and above ground biomass were significantly and positively related (P0.001).
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|---|---|---|
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