Study On The Shrub-grass Communities In Dry Warm Valley Of Jinsha And Lancang River

The climate characteristics of the dry valley in southwestern China are dry and hot or dry and warm,and the main vegetation type is shrub-grass community.The dry valley is one of the typical area with fragile ecology which are easily disturbed by human factors in Yunnan Province.The dry valleys distributed along the upper reaches of Jinsha River and Lancang River are the typical dry warm valleys.A large amount of research works in the past mainly focused on the middle and lower reaches of the river and few studies on the dry valleys in the upper reach,and there is no comparative analysis of vegetation and environmental factors in the dry warm valleys between Jinsha River and Lancang River.Deqin County belonging to Diqing Tibetan Autonomous Region is located in the most northwest part of Yunnan Province,and the population inhabited in Deqin County overlaps with the dry valleys.The shrub-grass community is the main vegetation type in the valley area,and is more susceptible to human activities.This study uses shrubs-grass communities in the dry warm valleys of Jinsha River and Lancang River in Deqin County as research objects to analyze the vegetation characteristics and the environmental factors.Vegetation data were obtained through field surveys,combining with the comprehensive analysis of climatic data and soil data.The results showed that:(1)The dry valleys of the Jinsha River and Lancang River reflect the climatic characteristics of the dry warm valleys,and the temperature and precipitation decrease along the river from the bottom up.The dry warm valleys in the Jinsha River have high temperatures and abundant heat,and the dry warm valleys of the Lancang River are relatively humid.The soils of both rivers are alkaline,and the nutrient content rises along the elevation,showing different patterns of changes along the river basin.The soil nutrient level in dry warm valleys of the Lancang River is higher than that of the Jinsha River.(2)A total of 48 species of plants were found in the dry warm valleys of the Lancang River.A total of 40 species of plants were found in the dry warm valleys of the Jinsha River.The species richness of the Lancang River was higher than that of the Jinsha River,and Gramineae were dominant in both rivers.The shrubs in community were dominated by smaller leaf plants.The herbaceous layer was dominated by grass.Vitex negundo var.microphylla,Bauhiniabrachycarpaare,Eragrostis pilosa,Cymbopogon distans are the dominant species shared by the two valleys.(3)The species diversity of dry warm valley in Jinsha River decreases with elevation,and increases from bottom to top along the river.The species diversity of dry warm valley in Lancang River decreases with elevation,and increases from bottom to top along the river and then decreases.(4)The shrubs with wide niche in the Jinsha River are Sophora davidii,Lespedeza fasciculiflora v.Hengduanshanensis,Potentilla anserina.The herb with wide niche are Eragrostis pilosa,Cynodon dactylon,Selaginella pulvinata.The shrubs with wide niche in the Lancang River are Bauhinia brachycarpa,Osteomeles schwerinae,Cotoneaster microphyllus,The herb with wide niche are Cymbopogon distans,Heteropappus altaicus var.Hirsutus,Eragrostis pilosa,Arthraxon hispidus.Eragrostis pilosaan has an advantage in the niche breadth of the two valleys.For the niche overlap,the degree of niche overlap in the Lancang River is higher than that in the Jinsha River.