Diversity Of Shrubs And Grasses In The Valley Of The Middle Reaches Of The Yarlung Zangbo River And Its Application In Ecological Restoration

The Qinghai-Tibet Plateau is of strategic significance to the ecological security of China and even the whole Asia.With its vast territory and high overall altitude,the regional ecological environment is affected by terrain changes and elevation fluctuations,and its temporal and spatial patterns change greatly.Therefore,it is extremely vulnerable and more susceptible to disturbance than plain and other regions,and it is extremely difficult to restore.The development of the Qinghai-Tibet Plateau has always been carried out in harmony with the policy of protection and development.In recent years,due to the dual effects of climate warming and man-made activities,the Qinghai-Tibet Plateau has faced a series of ecological challenges,such as melting of glaciers and perennial snow and frozen soil,degradation of vegetation and forest communities,and soil desertification.As the main body of the Qinghai-Tibet Plateau,the ecological restoration of Tibet directly determines the success of environmental protection on the plateau.Under the background of rapid social and economic development,a series of development and construction projects represented by Lalin Railway,Lari Railway and Linla High Grade Highway have been carried out successively.In addition,hydropower facilities and mine production are also being carried out closely.In terms of the distribution of these projects,the middle reaches of the Yajiang River valley are the most concentrated.As the political,economic and cultural center of Tibet,the ecological environment is under greater pressure.At present,the ecological situation in the middle reaches of the Yarlung Zangbo River valley is generally declining,so it is urgent to carry out scientific research on the vegetation in the middle reaches of the Yarlung Zangbo River Valley.In this paper,shrubs and herbaceous plants in the middle reaches of the Yarlung Zangbo River valley were studied.Through field investigation,combined with community site conditions,the characteristics and quantitative relationship of plant communities in the study area were comprehensively analyzed,and the relationship between plant community types and environment in the middle reaches of the Yarlung Zangbo River was revealed.The aim is to provide theoretical basis for species diversity conservation and scientific and effective phytoremediation measures in the middle reaches of Yarlung Zangbo River Valley.Main research conclusions:(1)In the valley of the middle reaches of Yajiang River,there are 28 species of shrub plants,Leptodermis pilosa,Leptodermis pilosa,Elsholtzia ciliata,Leptodermis microphylla,Ceratostigma minus,Cotoneaster multiflorus,Chelonopsis albiflora,Buddleja alternifolia,Sophora moorcroftiana,Parapteropyrum tibeticum,Buddleja lindleyana,Jasminum officinale,Desmodium racemosum,Spiraea salicifolia,Rabdosia oresbia,Rosa sericea,Damnacanthus indicus,Potentilla fruticosa,Rabdosia grandifolia,Spiraea mongolica(important value>1%),belonging to 12 families and 20 genera,and herbaceous plants,including Artemisia desertorum,Phtheirospermum japonicum,Astragalus strictus,Oryzopsis munroi,Tripolium vulgare,Eragrostis pilosa,Onosma waddellii,Chenopodium album,Poa annua,Stipa capillata,Aleuritopteris argentea,Conandron ramondioides,Gentiana scabra,Pennisetum centrasiaticum,Aster hypoleucus,Erigeron acer,Astragalus membranaceus,Oxytropis,Artemisia annua(important value>2%).,belonging to 13 families and 24 genera.Among them,Leguminosae,Rubiaceae and Compositae are the dominant families.Sophora moorcroftiana in the genus Sophora of Leguminosae,Leptodermis pilosa in the genus Syringa of Rubiaceae,and Tripolium vulgare in the genus Artemisia of Compositae have respectively become the constructive species of typical communities.(2)This paper introduces eight environmental factors as variables,including annual accumulated temperature above 0℃,maximum monthly average temperature,minimum monthly average temperature,annual temperature difference,average annual precipitation,solar radiation,slope,and altitude.The results show that the Simpson diversity index of shrub layer is negatively correlated with annual accumulated temperature above 0℃,maximum monthly average temperature,minimum monthly average temperature,solar radiation,and altitude,and is negatively correlated with annual temperature difference,annual average precipitation The slope is positively correlated.The Shannon-wiener index of shrub layer is negatively correlated with the accumulated temperature above 0 ℃,the highest monthly average temperature,the lowest monthly average temperature,solar radiation and altitude,and positively correlated with the annual temperature difference,annual average precipitation and slope.The Pielou evenness index of shrub layer is negatively correlated with the annual accumulated temperature above0 ℃,the highest monthly average temperature,the lowest monthly average temperature,solar radiation and altitude,and positively correlated with the annual temperature difference,annual average precipitation and slope.The Simpson diversity index of the herb layer is negatively correlated with the annual accumulated temperature above0 ℃,the highest monthly average temperature,the lowest monthly average temperature,solar radiation and altitude,and positively correlated with the annual temperature difference,annual average precipitation and slope.The Shannon-wiener index of the herb layer is negatively correlated with the annual accumulated temperature above0 ℃,the highest monthly average temperature,the lowest monthly average temperature,solar radiation and altitude,and positively correlated with the annual temperature difference,annual average precipitation and slope.The Pielou evenness index of the herb layer is negatively correlated with the annual accumulated temperature above0 ℃,the highest monthly average temperature,the lowest monthly average temperature,solar radiation and altitude,and positively correlated with the annual temperature difference,annual average precipitation and slope.(3)In the shrub layer,the dominant factors that contribute the most to Simpson diversity index are solar radiation and annual accumulated temperature above 0℃;The dominant factor that contributes the most to Shannon-wiener index is solar radiation;The leading factors that contribute the most to the Pielou evenness index are the annual temperature difference and the accumulated temperature above 0 ℃throughout the year.In the herb layer,the dominant factors that contribute the most to the Simpson diversity index are the annual accumulated temperature above 0 ℃ and the annual maximum monthly average temperature;The dominant factors that contribute most to the Shannon-wiener index are the annual accumulated temperature above 0℃and the annual average precipitation;The leading factors that contribute the most to the Pielou evenness index are the annual accumulated temperature above 0℃,the annual average precipitation,and the annual accumulated temperature above 0℃.(4)According to the important value of species and the breadth of niche,this paper selects the Sophora moorcroftiana,Ceratostigma minus,Leptodermis pilosa,and Tripolium vulgare as representatives,and constructs a multiple stepwise regression model to study the dominant factors affecting their distribution in various places.The research shows that solar radiation,annual accumulated temperature above 0℃,annual average precipitation,and minimum monthly average temperature are the variables that have the greatest impact on the distribution contribution rate of Sophora moorcroftiana,Ceratostigma minus,Leptodermis pilosa,and Tripolium vulgare.(5)According to the altitude and climate,the study area is divided into four transects.Corresponding measures and countermeasures for four ecological restoration plants.In the semi-humid area of 2900m-3100 m,Leptodermis pilosa is taken as the group building plant,and in the area where large shrubs are not easy to grow,Ceratostigma minus are taken as the dominant plant;The area of bare soil near large arbor communities is reduced by using Onosma waddellii and Chenopodium foetidum.In the dry and hot valley area of 3100m-3400 m,the way of Sophora moorcroftiana + Tripolium vulgare is adopted as the species of community building,supplemented by engineering measures to strengthen the degree of soil stability.The sandy locust is used as the group building species in the foothills and hillsides of the 3400m-3900 m semi-arid wide river valley,and the aquatic plants are used as the pioneer species in the bare river beach to improve the water content and soil nutrients of the soil first,and the top community plants of Artemisia desertorum + Tripolium vulgare are used for continuous improvement in the later stage.Semi-arid areas with an area of more than 4000 m should give full play to the advantages of native herbs,supplemented by engineering measures to reduce the source of sand.