干旱半干旱地区人工固沙灌木林生态系统演变特征

Evolution characteristics of the artificially re-vegetated shrub ecosystem of arid and semi-arid sand dune area

应用实验生态学方法分析了沙坡头地区栽植于1956、1964、1981、1987年的无灌溉人工植被固沙群落浅层土壤分形特征、植被盖度、物种特征、生物量、土壤水分、土壤微生物,以及群落土壤物理和土壤养分特征,并与流动沙丘进行比较.结果表明,在干旱半干旱的草原化荒漠地区,首先利用半隐蔽式草方格沙障对流动沙丘进行固定,然后栽植灌木柠条、花棒等和半灌木油蒿,经过40多年的稳定演变,该区域逐渐形成由矮灌木与草本植物覆盖,以及隐花植物与微生物土壤结皮复合的固定沙丘景观.在人工植被固沙防护体系稳定演变过程中,浅表层土壤的细粒化和养分富集化特征,微生物土壤结皮与亚表层土壤厚度,以及浅表层土壤体积含水率均随固沙年限的延长趋于显著增加.而土壤微生物数量、植被盖度、植物种数等生物群落学属性在固沙年限达40a左右时,已趋于最大,尔后呈缓慢下降趋势.随着固沙年限的增加,灌木树种不断衰退减少,当固沙年限逾17a之后,群落生物量增至峰值后略有下降.土壤分形维数与土壤粘粒含量呈显著正相关关系,流动沙丘被人工植被固定年代越久远,浅表层(0～3cm)土壤粘粒含量(4.50%)越高,其分形维数越大(D=2.4083),表明人工植被固沙防护体系浅表层土壤结构变得越紧实,流动沙丘(D=2.0484)在人工植被的固定作用下,发生逆转的趋势越显著,沙丘日趋固定.

The artificially established rainfed vegetation for stabilizing the shifting sand dunes in Shapotou area since 1956, using mainly the shrubs of Caragana korshinskii, Hedysarum scoparium and Arternisia ordosica at Shapotou Desert Experimental Research Station near Lanzhou has established a dwarf-shrub and microbiotic soil crust cover on the stabilized sand dunes. Soil particle size getting thinner and fertility, the depth of microbiotic soil crust as well as the subsoil, and the volumetric soil moisture in the shallow soil profiles increased remarkably associated with the process of sand dune stabilization. On the other hand, the number of microbe, the vegetation cover and the plant species attained a maximum degree when the dunes stabilized for 40 years. The shrub numbers and the community biomass decreased when the dunes stabilized for 17 years. There is a significant positive correlation between soil particle fractal dimension and the clay content of the shallow soil profile in the artificially stabilized sand dunes, the longer the dune being stabilized, the greater the soil clay content in the shallow soil profiles （0-3 cm）, the greater the soil particle fractal dimension （D=2.4083）. It reflects the fact that during the revegetation processes, the soil structure is strengthening and tightening in the shallow soil profiles. Hence, the shifting sand dune （D=2.0484） getting more stabilized. Therefore, the fractal model could be used to describe the texture and fertility states, and the stability degree of the formerly shifting sand dune, and it could be used as an integrated quantitative index to evaluate the re-vegetation practice in the sand dune areas and its stabilization.