| Desert riparian forest dominated by Populus euphratica and Tamarix is the core of the desert ecological environment in the lower reaches of Tarim River, which is of great significance in desert ecological environmental protection, restoration and reconstruction.Desert vegetation biomass accumulation is the result of interaction between environmental factors, not only embodies the ability of desert ecosystem for energy, and instructions for desert ecological environmental changes. This study based on the groundwater monitoring wells in the lower reaches of the Tarim River, through harvest desert vegetation aboveground biomass and using mathematical statistics method, aboveground biomass estimation models of dominant species are established by using the measurable indicators(base diameter,diameter at breast height, tree height, crown amplitude, etc.). Finally, analyzing the desert vegetation aboveground biomass spatial distribution characteristics and the relationship between the groundwater depth based on established biomass estimation models and an vegetation transect investigation along the vertical direction of the river. The main conclusions are as follows:(1)The power function model W?=0.051d2.224(R2=0.753,RSS=7.092)which by using d(d refers to basal diameter of branch)as independent variable was best to estimate the leaves biomass of Populus euphratica,and increased the variable h(h refers to the length of branch)didn't improve the effect of model.While the best model used to estimate single branch was established taking d2h as parameter,and the model was W?=0.429(d2h)0.584(R2=0.913,RSS=2.833).The equation model W????=0.298(D2H)0.775(R2=0.966,RSS=1.565)which by using D2H(D and H refer to diameter at breast height and tree height,respectively)as parameter was best to estimate the aboveground biomass of P.euphratica.(2) Based on field measured data, the aboveground biomass estimation model of Tamarix chinensis is established. The model, Ma =0.123(d2h)1.241(R2=0.844,F=636.865)( Ma, d and h refer to single branch biomass, basal diameter and length of branch, respectively), which by using d2 h as independent variable was best to estimate the biomass of single branch, the accuracy of it was 76.93%. Mb =1.335(SH)0.806(R2=0.788,F=174.678) and Mc=0.924S1.289(R2=0.771,F=158.358)were single cluster biomass estimation models of T.ramosissma, they were built taking crown area, crown area and height as independent variables respectively,whose estimation accuracy was 76.04%, 72.83%. The differences between measured value and estimated value of all three biomass estimation models above were analyzed by Chi-square test, the result shows that there was no significant differences between them.(3) Depth of groundwater is the main factor affecting the desert plant aboveground biomass.Regression analysis on the net primary productivity(NPP) of different groundwater depth and established the herb NPP model The model, y=-3.7205x2+22.122x+53.105( R2=0.9012,F=123.14),(x, y refer to depth of groundwater and NPP, respectively). Sensitivity analysis of the model shows that when groundwater levels more than 7.0 meters, the variation of NPP exceeds more than 10% in response to variation of 0.1 meters to the depth of groundwater,that the variation of groundwater level has significant effect on NPP of herbaceous plant.Therefore, depth of groundwater is equal to 7 meters can be regarded as the water stress depth of herbal subsist in the lower reaches of Tarim river.(4) It showed a negative correlation between aboveground biomass spatial distribution of desert vegetation and its vertical distance from river(P<0.05), the total aboveground biomass mainly distributed in 0-1000 meters and decreased significantly when distance beyond 1000 meters. Aboveground biomass of P. euphratica mainly distributed in 0-300 meters and1400-2000 meters, aboveground biomass of shrub reached the maximum at 300 meters and the largest value was 629.9 g/m2, it would have a sharp decrease when the distance was about1300 meters from river, at the same time, aboveground biomass of T. chinensis reduced and the composition of Halostachys caspica, Lysium rothenicum and Karelinia caspica were on the rise. Aboveground biomass of shrub showed a stable change and biomass could reach 50g/m2. Aboveground biomass of herb showed a single peak type change with the distance changed from river, the species of herb was rich and biomass increased with the distance ranged from 0 to 1000 meters, beyond this distance, the species and biomass were in decline. |
PDF Full Text Request