The Research On Plant Community Structure And Dominant Species Pattern In The Lower Reaches Of Tarim River

Taking communities in the transported lower reaches of Tarim River as the research object and communities in non cutting off middle reaches of the Tarim River as the reference system, we comparatively analyze the structure characteristics of communities in the middle and lower reaches of Tarim River, and using ground survey data and high-resolution remote sensing (quick-bird), analyze and contrast community structure and the spatial pattern of dominant species, which provide the basis for correctly evaluating watering results.The difference between community structure in the lower reaches of Tarim River and that in middle reaches of Tarim River is obvious, which shows:Community composition structure: There are 13 common species in inquiry period in the downstream of Tarim River, among which Populus euphratica, Tamarix and Alhagi sparsifolia are dominant species; Investigated species are relatively abundant in the corresponding period in the middle of Tarim River where 26 species exists, among which Populus euphratica and Tamarix are dominant species. Communities species diversity index, species abundance and evenness in middle reaches are higher than those in downstream, which shows features that plant species are lack in downstream and the system degenerates.Community density structure: The density of trees, shrubs and herbs in downstream on the whole tend to decreasing with distance from the river increasing; The density of trees and shrubs in middle reaches decreases with distance from the river(or age) increasing, while herbaceous layer density shows wavy changes with the age of main canopy of populus euphratica increasing.Community vertical structure: In the lower reaches of Tarim River Community vertical structure is simple, which changes from trees, shrubs and herbs three layers to shrubs and herbs two layers with increasing distance from the river; Community vertical structure shows tree-shrub-herb three layers on the whole, accompanying by a small amount of plant between layers in middle reaches of Tarim River.The diameter structure of dominant species populus: Within 300m from the river in downstream, because populus root sprouts after water, populus'diameter appears irregular mountain figure or anti-J-curve of different age forest. Within the distance of 1050m to 1500m from river the diameter is almost in big bands and small amount of plant. Populus euphratica diameter structure in the middle of the river has obvious regularity, yong age showing anti-J-curve, middle-age showing negative deviation, mature forest showing similar normal distribution, over mature forest showing anti-J-curve far away from the river. Populus euphratica forest age structure in middle reaches possesses young, middle, nature and over age with the distance from river increasing and the stand form is regular and continuous. Populus euphratica forest in lower reaches tends to diameter class deletion or trees deletion in different distances from the river due to long periods of cutting off and the stand form is broken.Through employing ground survey in middle and lower reaches of Triam River and high-resolution (quick-bird) remote sensing data in downstream to analyze species pattern of Populus euphratica and Tamarix, the same conclusion of both methods in the same region obtains. The results are as following:Populus euphratica distribution pattern: Both remote sensing and ground survey analysis indicate that Populus euphratica distribution pattern shows aggregated distribution in different distances from the river in the downstream of Tarim River, the gathered strength enlarging with density reducing, the plaque area enlarging with the distance from river increasing. Populus euphratica distribution pattern of young and over-old age forest is gathered distribution in the middle of Tarim River and middle and mature age forest randomly distributed. There is not inevitable relationship between gathered strength and density and pattern scale shows that plaque area of over mature forest is larger than young.Tamarix individual plant (clump) distribution pattern: Tamarix distribution pattern shows aggregated distribution in different distances from the river in the middle and downstream of Tarim River; Gathered strength is stronger in the non dominant section than that in the dominant section where showing spreading out trend. Pattern scale in the dominant area of Tamarix in the middle and lower reaches (outside 300m in downstream, middle age and over mature forest in the middle reaches) is 16m×32m and plaque size does not appear in the non dominant section because of the litter Tamarix density or restrictions of plots area.