Community Character And Eco-hydrological Function Of Subalpine Meadow In Wolong Nature Reserve

The subalpine meadow and eco-environmental conditions at the source area of Wolong Nature Reserve were investigated. By the means of Detrended Correspondence Analysis (DCA) ordination and Two Way Indicator Species Analysis (TWINSPAN ) classification the ecological relationship among the communities and between the community and the environmental factors were studied. On the basis of the subalpine meadow mechanism of water-conserving,the hydrological process of canny layer and soil layer for vegetations and characteristics for water conservation function have been analyzed. The evaluation index system of water-conserving function has been put forward to. Conclusions are as follows: (1) There are 139 species of plants in this subalpine zone. They belong to 30 families and 108 genera, which are dominated by Compositoe, Liliaceae, Orchidaceae, Pleurosperum, Scrophulariaceae, Polygonaceae, Ranunculaceae and Gramineae. Based on the field investigation of 114 sampling plots in Wolong Nature Reserve, the species composition and community structure of subalpine meadow communities were analyzed. The two-way indicator species analysis and the detrended correspondence analysis were employed to classify and ordinate subalpine meadow communities from 114 sampling plots in order to understand key influencing factors determining the structure and distribution pattern of subalpine meadow communities. The subalpine meadows were classified into 12 types through TWINSPAN analysis. There are Deyeuxia scabrescens+Anaphalis bulleyana+ Polygonum viviparum,Deyeuxia scabrescens+Polygonum viviparum+Pedicularis davidii, Stellera chamaejasme+Polygonum viviparum, Parnassia delavayi+Polygonum viviparum+ Deyeuxia scabrescens, Deyeuxia scabrescens+Polygonum viviparum, Taraxacum lugubre+ Stellera chamaejasme, Stellera chamaejasme+Taraxacum lugubre, Caltha palustris+ Polygonum sphaerostachyum, Kobresia sp.+Stellera chamaejasme+ Caltha palustris, Caltha palustris+Trollius ranunculoides+Taraxacum mongolicum, Iris delavayi+Deyeuxia scabres-ens, Caltha palustris+Pteris bakerianum. (2) DCA ordination of those communities demonstrated that Axis2 indicated a significant relationship between meadow distribution and soil humidity; while Axis1 indicated an important relationship of meadow distribution with altitude, along the gradient of which the communities were distinct from each other. The result of DCA ordination was similar to that of TWINSPAN classification, which reflected the relationship among the communities and between the community and the environmental factors. The quantitative analysis method not only provided the interpretation to the communities and the environmental gradients but also objectively elucidated the relation between the communities and the environmental factors. The analysis results showed that the importance of environmental factors affecting the structure and distribution pattern of subalpine meadow communities were soil moisture and altitude. The communities at this zone play very important roles in improving the conditions of soil and climate, conserving water and maintaining ecological balance. (3) Based on the data from field survey species richness ,αdiversity and βdiversity of the subalpine meadow in Wolong nature reserve ,Sichuan Province, we are analyzed in this paper .The results were as follows: Species richness index was the highest at mid-altitude. Αdiversity indices (Shannon-Wiener index and Simpson index) increased firstly ,then decreased with altitude increasing . Pielou evenness index increased with altitude increasing obviously. βdiversity indices (Cody index and Wilson-Schmida index),increased with increasing altitude. (4) The saturated water-holding capacity of leaves in different communities ranged from 1.00mm to1.40mm,Stellera chamaejasme community was the largest. The available water-holding capability of leaves rate which was the same as saturated water content rate were Stellera chamaejasme community(1.26mm), Deyeuxia scabrescens community(1.06mm), Caltha palustris community(1.10 mm)and Iris delavayi community(0.86mm) (5) There are better physical attributes and high water-holding capability in subalpine meadow soil. The maximum water storage of Caltha palustris community, Stellera chamaejasme community, Deyeuxia scabrescens community and Iris delavayi community were 3242 t/hm2,3193t/hm2, 3213t/hm2,2704t/hm2 in 45cm depth respectively. (6) The initial infiltration rate of Caltha palustris community, Stellera chamaejasme community, Deyeuxia scabrescens community and Iris delavayi community were 16.89 mm/min, 12.57mm/min, 7.33 mm/min and 2.36 mm/min;stable infiltration rate were 9.03 mm/min, 10.37 mm/min, 4.72 mm/min and 1.26 mm/min;cumulate infiltration content in 30mins of Caltha palustris community was higher than other subalpine meadow,time of reaching stable seepage of Iris delavayi community was the shortest. So, the soil infiltration property of Caltha palustris community and Stellera chamaejasme community were superior and the function of regulating the water during the process were marked. We concluded that rainfall intensity was not reach or overrun the stable infiltration rate in all subalpine meadow communities, so surface runoff over infiltration state seldom occured. (7) The soil water varied with time, flatuating during the growing season. The vetical variation of soil moisture indicated to different patterns among the three spatial layers.(8) The method of Analytic Hierarchy Process was applied to establish the hierarchy structure model and evaluation index system of vegetation community .The method of expert assessment and integrative grades were applied to assess the water-holding function of vegetation community. The index value ranges from 2.8 to 8.0. The water-conserving function of community shows as follows: Stellera chamaejasme community> Caltha palustris community> Deyeuxia scabrescens community>Iris delavayi community...