Spatial Distribution Of Plant Communities And Environmental Interpretation In Minqin Oasis-Desert Ecotone

Due to the special role as connection corridor between oasis and desert, Oasis-Desert Ecotone was a key area to carry out research on ecosystem degradation andrecovery mechanism in arid region. In this paper, the plant communities in the Oasis-Desert Ecotone of Minqin (Minqin ODE) were selected as case study. Based on theinvestigation of typical desert plant communities and environmental factors, we studiedthe desert plant communities in Minqin ODE by the means of two-way quantitativeclassification and ordination in order to reveal the environment gradient of main plantassociation’s distribution. The preliminary results as follows:(1) The spatial difference of groundwater depths in Minqin is obviously. Groundwaterdepths of oasis plains areas are greater than the edge desert area. Two larger groundwaterfunnel shape are located near the city of Minqin in Baqu and Liujiadi in the Quanshanqu.In2010, the max groundwater depth is34.33m, the min is2.2m, and the mean is15.82m.(2) In Minqin ODE, the structure of vegetation communities is simple and the species ofplants have the characteristic of drought resistance and salt tolerance; According tospecies important value, there are12dominant species in Minqin ODE. That is:H.ammodendron, N.tangutorum, T.ramosissima, R.soongarica, K.foliatum, L.ruthenicum,A.arenaria, P.australis, A.squarrosum, H.glomeratus; The results of plant communitiesstructure analysis show that each of dominance species distributed in aggregative state.The species diversity indies of these communities were low and species diversity showedgradient change. The richness index followed the order: Baqu> Quanshanqu> Huqu.(3) Classification of vegetation is conducted by using two way indicator species analysis(TWINSPAN). The outcome of TWINSAN shows that the desert plant communities inMinqin ODE were composed of11plant associations. The main associations includingN.tangutorum+H.glomeratus, N.tangutorum+P.australis, N.tangutorum+K. foliatum,K.foliatum+L.ruthenicum etal. Meanwhile, the succession trends of Minqin ODE alsobe reflected spatially in the classification result. According to the principle of China PlantClassification, there are4vegetation types,5vegetation subtypes,10formation groups,20associations. (4) The samples of fixing vegetations in the picture of samples CCA ordination weredivided into5areas, named A, B, C, D and E, each of them corresponding to their sitetype and ecological conditions.The influences degree of environmental factors from theCCA ordination in N.tangutorum communities show that: SW> Sad> Sit> Cly> EC>AP> SOM> Dep> Alt> TN> pH> Dis. Obviously soilwater and soil texture are thedominant factors of distribution of fixing vegetation.(5) The artificial H.ammodendron communities were divided into3associations:H.ammodendron+B.dasyphylla, H.ammodendron+Calligonummongolicum+A.squarrosum, H.ammodendron+N.tangutorum+A.squarrosum. The statistical characteristicof environmental factors reflects the difference of3associations.The effects of obtainedenvironmental factors on the distribution of artificial Halxylon ammodendroncommunities are ordinated: Sad> Cly> Sit> SOM>SW> Dep> Dis> pH> EC> TN>Alt. Obviously, the dominant environment parameters are soil texture, soilwater and soilorganic matter.(6) The environmental conditions of N.tangutorum communities are the determinantfactors of the succession stages in the study areas. Combined the second levels ofTWINSPAN and the realistic and ecological features of samples, the N.tangutorumcommunities are divided into: N.tangutorum+P.australis, N.tangutorum+A.squarrosum,N.tangutorum+H.ammodendron+A.arenaria. Among3associations, the maxgroundwater depth is21meters and the min is7.07meters, corresponding to associationIII and I respectively. The ordination of soilwater in the3associations: ClassificationI(11.37%)> Classification II(8.9%)> Classification III(3.84%). The soil mechanicalcomposition in3associations is similar. The ordination of distance between samples andoasis in the3associations: Classification II (3.1Km)> Classification I (2.7km)>Classification III(2.6km). The influences degree of environmental factors from the CCAordination in N.tangutorum communities shows that: Dep> SW> pH> SOM> Dis> AP> Cly> Sad> Sit> EC> Alt. Therefore, Dep and SW are the determinant factors in thedistribution of N.tangutorum communities.