Population Diversity Of Plant Community In Hexi Mountain Oasis Desert,Gansu,China

This paper mainly search for the fundamental characteristics of population diversity in plant communities occurring in the multi-ecosystem consisted of the north Qilian mountain, Zhangye oasis and desert. Some related theoretical issues were also discussed. 1 General features of ecological geography and major types of plant communities The sampling area consists of three geographic sections, i.e. midsection of the northern Qilian mountain forestry grassland section, Zhangye desert-oasis section and Dongdashan mountain forestry grassland section. The altitude ranges from 1450m-4200m.The climate variation trend over the last 50 years is relative lower temperature with richer precipitation in the area. Accordingly, the glacier in Qilian mountain would be stable or advance . The runoff dynamics of Heihe river has the same trend with the precipitation. The main plant community types in the sampling area are mountainous desert grassland, typical grassland, Picea cra.csifolia forest ,Sahina przewal.ckii forest ,Caragana juhata桽ahx oritrepha shrubland, Salsola passerifla desert , Svrnpegma regelii desert and Reaumuria soogorica desert. There are total 1064 vascular plant species in this area.The floristic characteristics of Zhangye desert is quite different from that of Qilian mountain and Dongdashan mountain . The former has a relative old origin ,however, the latter has young and derivative floristic characteristics. There are 5 types of plant life spectra, i.e., Hemicryptophytes , Phanerophytes, Therophytes ,Cryptophytes and Chamaephytes. Hemicryptophytes is the dominant plant life spectra. 2 The changes of population diversity along the altitudinal gradient The change of both richness and diversity in Potent Ella fruticczsa shrubs shown the same trends along the altitudinal gradient. The highest richness and diversity occurred in the mid- altitudes area from 2580m to 2650m. The lowest is at the altitude of 3590m. However, the highest evermess index occurred in the altitude scope of 3200m to 3590m. The richness of Picea crass~folza forests decrease with increased altitudes. The changes of diversity shown a hump-backed curve along the altitudinal gradient. Among the 3 P,cea crass~folia forest series~ shrub -s- Picecz crass ~folia forests have the highest richness and diversity, the middle is 5 Carex sp. + Picea crass~folia forests and the lowest is Abietinella sp,+Picea crass~fo(ia forests. The evenness is higher in the mid-altitudes ranges. The richness and diversity is higher at the mid-altitudes in the grassland communities. The changing trend represented by grassland types is montane typical grassland (2350m-2950rn) > montane desert grassland (lSOOm-2350m) > subalpine grassland (2950m-3700m) > desert grassland (1 500m-l SCOrn) . The evenness indices shown much fluctuations within the entire ranges of altitude. 3 The changes of population diversity in different layer of a given plant community The change trends of richness in 3 layers of Sob ma przewalskii forests was herb layer> shrub layer> tree layer. No distinct trends were observed in the change of diversity in three layers. The Picea crass~folia forests vertical distributes with a larger scale of altitudes. The change trends of richness in 3 layers of shrub + Picea crass~folia forests and Abietinella sp.+ Picea crass~folia forests was shrub layer >herb layer> tree layer and herb layer> shrub layer>...