The Plant Community Distribution Patterns And Its Driving Forces Of Typical Wetland In Northwestern Yunnan Plateau, China

Wetlands in northwestern Yunnan plateau, situated in the upstream of the Yangtze river and Mekong River, are unique plateau wetlands in China, which play key roles of adjusting the water and biodiversity conservation for middle-lower reaches of the rivers; Meanwhile, for its lying the transition region of farming and grazing and noted as beauty spots, where yarded up many minority such as Tibetan, wetlands were regarded as the strategic resources for local economic development and society stabilization.Wetland plants are focus of structure-function of the wetland ecosystem and sensitive indicator of the changing wetland environment. With non-wise using wetland resource, as a reaction to changed wetland environment, the distribution patterns of wetland plant communities have also altered, which affect the functions of wetland ecosystem and endanger ecological security of middle-lower reaches of Yangtze river and Mekong river and peripheral regions. Napahai, typical degraded wetland in northwestern Yunnan plateau, has been choosed as studying plot, and been divided into primary marsh, swampy meadow, meadow and reclaimed wetland during the succession process of wetland according to its hydrology, plant types and human disturbance. Using 3S technology and plant community research methodology, the temporal-spatial substitution methodology was applied to study the distribution patterns of wetland plant communities, analyze its relationships with the changed wetland environment and its main driving forces, discuss the ecological process and succession principle of its distribution patterns, and provide the scientific theory for wetland plant resource conservation decision, wise use and degraded wetland ecosystem restoration.The results showed that Napahai Wetland has 115 species, belonging to 38 families and 82 genera, including 3 submerged plant communities, 2 floating-leaved plant communities, 6 emergent plant communities and 4 meadow plant communities. For the primary swamp there were 25 species, belonging to 16 families and 17 genera, including 3 submerged plant communities, 2 floating-leaved plant communities. For the swampy meadow, there were 36 species belonging to 19 families and 26 genera, including 6 emergent plant communities. For the meadow, there were 64 species belonging to 28 families and 55 genera, including 4 meadow plant communities. For the reclaimed wetland there were only 4 species belonging to 4 families and 4 genera. The distribution patterns of plant communities have changed with the wetland succession from primary swamp to swampy meadow, meadow and reclaimed wetland, the number of communities increased firstly and decreased latterly , community structure become complex, the companying species increased and the dominant species decreased. Aquatic plant communities mainly distributed, Submerged plant communities mainly distributed in northwestern limited deep water area of wetland, emergent plant communities distributed in shallow water area or interval inundation area, floating plant communities distributed in limited area of the mouth of spring and sinkage, meadow and reclaimed plant communities took up the largest area of around the wetland. Submerged plant communities, floating plant communities and emergent plant communities stratified notability, while the meadow and reclaimed wetland plant communities did not, compared with the aquatic plant communities 24a before, the types and numbers of aquatic plant communities changed, and pollution-tolerant, nutrient-loving plant communities flourished while primary aquatic plant communities shrank or disappeared. the number of aquatic communities has increased from 9 to 12, with two new emergent plant communities and one new floating-leaved plant community. The increase in emergent plant communities was most marked. The current distribution area of emergent plant communities, 528.42hm2, is the largest; submerged plant communities cover 362.50hm2; and the distribution area of floating-leaf plant communities is the smallest, covering 70.23hm2. The distribution pattern and change in Napahai wetland's plant communities is a reaction to the change in the wetland environment. The species richness and the pant diversity index increased as primary swamp changed to swampy meadow and meadow, the highest species richness occurred in the meadow and the lowest was in the reclaimed wetland, the diversity kinds have changed; with wetland succession from primary swamp to swampy meadow to meadow, soil organic matter, total N declined, soil enzymic activity of Catalase,Protease,Invertase increased while Urase declined. Plant species diversity of Simpson index and Shannon-Weiner index all increased successively. There existed negative correlation between Catalase,Protease,Invertase and soil organic matter,total nitrogen; Urase positively correlated with organic matter and total N. Index of Simpson,Shannon-Weiner negatively correlated with organic matter and total N; Simpson,Shannon-Weiner index positively correlated with Catalase,Protease,Invertase, negatively correlated with Urase, the correlation between plant species diversity and Invertase was the most evident. species composition,community coverage and accompany species negatively correlated with organic matter,total N and Urase, positively correlated with Catalase,Protease,Invertase; With the deflected succession of aquatic ecotype plant functional group the dominance of mesophytes and xerophytes increased while the dominance of aquatic and hygric plants decreased However, there are only planting crops in the reclaimed wetland. In the composing of plant biotype functional group the hydrophytes reduced quickly with the deflected succession and the dominance of perennial herbs is mostly marked and there are only annual herbs in reclaimed wetland; The landscape have changed from primary swamp, swampy meadow to meadow and reclaimed wetland gradually, the spatial distribution variation of landscape diversity of plant communities in different succession stage is of wetland responses to human disturbances. That reflects the changes of aquatic environment and the function status of the wetland and the type and intensity of the human disturbance. Through analyzing the ecological formative process of plant communities distribution patterns in Napahai Wetland and its mode of wetland resource use, the main disturbances are drainage, reclamation, unmanaged tourism, overgrazing in the wetland and vegetation destruction in watershed.The wetland plant community distribution pattern is the one of main indicators of degraded wetland ecosystem, showed its changed structure and its retrogressive functions. With the study, to protect the wetland ecosystem and restore the degraded wetland is to strengthen management of human activities, restore the wetland hydrology and achieve the wise use for the wetland resources.