玛曲高寒草甸沙化过程中群落结构与植物多样性研究

Abstract

Maqu alpine meadow is the important part of the Qinghai-Tibet Plateau and the main water conservation area in the upper reaches of Yellow River. But in recent years,the problems of the sandy desertification and soil erosion have become a serious threat to the ecological safety of the alpine meadow in the Qinghai-Tibet Plateau. To solve these problems,this paper examined the vegetation structure characteristics and the variation of α and β diversity on the potential,slight,moderate and serve desertification meadows in Maqu alpine meadows using sampling survey methods from July to September2008. The results showed that in the desertification processes of Mqu alpine meadows,1) the community coverage droppedgradually( 99. 216%,80. 078%,49. 895% and 36. 398%,respectively),the species number also reduced gradually( 53,32,14,13,respectively),community structure took a trend of simplification( the number of the dominant species were 28,16,10,8,respectively). The typical dominant and companion species of the alpine meadow also withdrew from the communities gradually,and the species adapted to the sandy environment occupied an important position in these plant communities. The typical Maqu alpine meadow ecosystem was gradually changing to the desertification alpine ecosystem,and experienced four stages,i. e.,Carex moorcroftii+Poa alpina communities→Carex moorcroftii +Saposhnikovia divaricata+Kobresia pygmaea communities → Kobresia pygmaea + Saposhnikovia divaricata + Carex moorcroftii communities → Leymus paboanus + Corispermum tibeticum + Carex moorcroftii + Saposhnikovia divaricata communities. 2) The species richness,Shannon-Wiener indexes and Simpson indexes were declining significantly. The Pielou evenness indexes and Alatalo evenness indexes showed a decreasing trend following the first increasing,and it reached the maximum in the slight desertification meadow,but their differences were not significant. The dominant index was increasing significantly,and there was extremely significant difference between the moderate desertification meadow and the slight one. 3) In terms of Whittaker index,there were extremely significant differences between the potential desertification meadow and other three ones,and there was significant difference between the moderate desertification meadow and the severe one,whereas there was no difference between the slight desertification meadow and the moderate one. 4) The community dissimilarity coefficient between the potential desertification meadow and other three ones were greater( the value in the range of 0.705—0. 937),while the community common indexes between them were lower( the value in the range of 0. 034—0. 173),and the trend between the slight desertification meadow and the severe one was similar. However,the community dissimilarity coefficients between the moderate desertification meadow and severe one and the slight desertification meadow and the moderate one were lower( the value in the range of 0. 545—0. 553),and the community common indexes were higher( the value in the range of 0. 293—0. 303). The analysis from all the results revealed that the slight and severe desertification stages were the most important phases in the desertification process of Maqu alpine meadow. So,the potential desertification meadow must be protected and managed scientifically in order to prevent desertification from occurring.Artificial measures,e. g.,enclosure,rotational grazing and tending were applied. However,in the sandy desertification meadows,vegetation restoration measures,such as turf transplantation,reseeding,fertilization as well as sand control measures must be taken to prevent the exacerbating and spreading of desertification.