不同沙源供给条件下柽柳灌丛与沙堆形态的互馈关系——以策勒绿洲沙漠过渡带为例

以塔克拉玛干沙漠南缘策勒绿洲—沙漠过渡带为研究区域,根据沙源供给丰富程度的明显差异,在固定沙地、半固定沙地、半流动沙地和流动沙地随机选择100个相对独立的柽柳灌丛沙堆,对每个沙堆形态进行测量,并对沙堆上的柽柳灌丛进行调查,分析研究不同沙源供给条件下柽柳灌丛形态特征和沙堆形态变化及其相互关系。结果表明:(1)在4种沙源供给条件下,柽柳灌丛高度相对稳定,灌丛长度、宽度、树冠投影面积、总枝条数、新枝率、基部新枝率和生物量随着沙源供给丰富度的增加而相应增加。(2)随沙源供给丰富度的增加沙堆尺度显著增大,外形向着沿风向拉长的不对称圆丘状发展,风影沙尾轮廓逐渐清晰。沙堆形态参数间存在良好的相关性,其中长度与宽度协同增长,回归曲线在流动沙地为二次函数关系,在其它3种沙地呈线性相关;底面积与高度表现为良好的二次函数关系;底面积与体积间存在显著的线性关系。(3)柽柳灌丛形态参数与沙堆形态参数间存在良好的相关性。其中树冠面积与沙堆体积间为显著线性关系,而树冠大小又与总枝条数以及新枝率密切相关,柽柳灌丛沙堆的适应机理应归于不断增加的沙源供给而产生的风积沙埋对柽柳灌丛生长的促进作用及灌丛与沙堆间的互馈效应。该区域柽柳沙包的形成以一定灌幅的存在为前提,可以判定是土地退化的产物,其中半流动沙地生境相对于其他沙地正处于急速退化中。

Research on the morphological interactions between Tamarix ramosissima thickets and Nebkhas under different sand supply conditions:a case study in Cele oasis-desert ecotone

In order to understand the morphological interactions between Tamarix ramosissima nebkhas and Tamarix ramosissima thickets in the oasis-desert ecotones, 100 independent Tamarix ramosissima nebkhas were randomly selected under different sand supply conditions in the northwest oasis-desert ecotone of Cele at the southern rim of the Taklimakan Desert. According to the difference in vegetation coverage and land surface characteristics, we divided the 100 nebkhas into four categories under four sand supply conditions (i.e. fixed sandy land, semi-fixed sandy land, semi-shifting sandy land and shifting sandy land), corresponding to poor, less poor, rich and richer sand supply conditions respectively. In field, the morphological parameters including the nebkhas' length, width, height, windward slope length and leeward slope length of nebkhas, together with thickets' height, length, width, crown area and different kinds of branch number were investigated. The results indicated that: (1) Increasing sand supply led to the increase of Tamarix ramosissima thickets' length (P=0.03), width (P=0.041), crown area (P=0.032), branch number (P=0.003), new branch rate (P=0.002), rate of basal new branch (P=0.000) and biomass (P=0.001), while the plant height (P=0.929) retained invariable. The average values of these parameters were respectively 6.85 m, 7.23 m, 42.14 m², 418.0, 49.3%, 45.0% and 65.8 kg in shifting sandy land, which were the largest among the four sandy lands. (2) Tamarix ramosissima nebkhas' height (P=0.000), length (P=0.000), width (P=0.007), underside area (P=0.001), volume (P=0.001) would significantly increase with sand supply enrichment. In shifting sandy land, the above corresponding average values of nebkhas' parameters were respectively 1.83 m, 14.16 m, 7.93 m, 76.64 m² and 86.33 m³, which were larger than the other lands. The nebkhas figure would develop into a long and narrow with the leeward slope becoming longer than the windward slope and the outline of sand dune tail would also become clearer. At this area most of nebkhas were still at a growing stage. The nebkhas in semi-shifting sandy land had the largest growth space, which's height would be near 4 m. (3) There were good morphological relationships among morphological parameters of Tamarix ramosissima nebkhas, the nebkhas length and width showed a coordinated growth trend with a quadratic polynomial regression equation in shifting sandy land, while a linear relationship in other sandy lands. There was a quadratic polynomial relationship between nebkhas underside area and height, and nebkhas volume increased linearly with the enlargement of underside area. (4) The Tamarix ramosissima thickets and nebkhas also exists good morphological correlation, among which the crown area and nebkhas volume showed a significant liner relationship. The adaptability mechanisms of Tamarix ramosissima nebkhas might be the stimulative function of comparative deep sand-burial as a result of wind accumulate with high-intensity to the growth of Tamarix ramosissima nebkhas and the feedback effect between the thickets and nebkhas. The conclusions indicated that the Tamarix ramosissima nebkhas in this area are the product of land degradation, and the semi-shifting sandy land is in a swift degeneration process now.