Study On Quantity Characteristics And Species Composition Of Three Vegetation Patches In Alpine Meadow On The Northeast Range Of Tibet Plateau

The formation and evolution of vegetation patches is one of main researches in the grassland ecology,which affects its successional dynamics and development direction.This study on quantity characteristics and species composition of grassland vegetation patches will reveal the ecological mechianism of vegetation changes and community succession of grasslands.We analysed the quantity,area,size,shape,and vegetation composition and soil nutrients of Leontopodium nanum,Kobresia humilis and Kobresia pygmaea patches under two grazing intensities alpine meadows on the Tibetan Plateau,and revealed the chage characteristics of this three vegetation patches and their adaptive strageties for the microsites and nutrient resource utilizations in this research.The main results were as follow:1)Under two grazing intensities grasslands,the number of Leontopodium nanum and Kobresia humilis patches was middle grazing intensity pasture(MG)﹥heavy grazing intensity pasture(HG),the individual size of patches was MG﹤HG,but the grazing intensities had no signicacant effect on the number and size of Kobresia pygmaea patch.Animals grazing can reduce the big vegetation patches proportions and increase the small vegetation patches proportion in the two grasslands.2)The shape of Leontopodium nanum patch occupied mainly by polygon,with a low stability but high expandability and recuperability habitat characteristic,which belonged to the survival strategy of first possessing resources and then using them.While the shapes of Kobresia humilis patch exhibited by circle and annulus and the Kobresia pygmaea patch largely composition by the circle,triangle and gourd-shaped,respectively,and this two patches had a high stability but low expandability and recuperability habitat characteristic,which belonged to the survival strategy of spoliating resources.Kobresia humilis patch had a strong resources occupying ability,so it can prevent the other species invading.3)The number of species,Gleason index and Whittaker index of this three vegetation patches were Patch ﹤ Patch-CK and CK.Eexcept the Mountford similarity index of Kobresia pygmaea patches,the Jaccard,Sorenson and Mountford similarity indeices of Leontopodium nanum and Kobresia pygmaea patches were patch/patch-CK=patch-CK﹥patch/CK,while the Jaccard,Sorenson and Mountford similarity indeices of Kobresia humilis patches were patch/CK=patch-CK /CK﹤patch/ patch-CK.4)The biomass composition difference of this three vegetation patches mainly reflected in gramineae,cyperaceae,leguminosae and asteraceae.The contents of soil mineral nutrition exhibited some differences among the patch types,patch sites and mineral nutrition types.The difference of K contents of Leontopodium nanum or Kobresia humilis patches,and the N,P and K contents of Kobresia pygmaea patch was significant in different patch sites.The soil Cu、Fe and Zn contents were susceptible to vegetation patches formation,while it was no susceptible for the soil Mg and Mn contents.The soil N,K,Cu,Fe,Mg,Mn and Zn contents had significant difference in different patch sits.Animals grazing could encourage the vegetation patches miniaturization and fragmentation,and the vegetation patches formation can break the coexistence pattern of multiple species.The difference in shape of the three patches suggests that they have an adaptive selection for different microhabitats and nutrition resource utilization.