浑善达克沙地四种生境中榆树天然更新幼苗发育的比较

对浑善达克沙地腹地风蚀低地、覆沙草地、平坦流动沙地和流动沙丘阴坡 4种类型生境中植物群落和榆树幼苗生长的比较研究结果表明 :(1)尽管单个样方内植物种数生境间没有差异 ,但群落总盖度覆沙草地的最低 ,流动沙丘阴坡上的居中 ,风蚀低地和流沙平地的最高。榆树幼苗的分盖度风蚀低地的最高 ,在流沙平地的次之 ,在覆沙草地的最低 ,流动沙丘阴坡的介于流沙平地和覆沙草地的中间 ,但与二者没有显著性差异 ;(2 )风蚀低洼地的幼苗生长的最好 ,平均高度、主根长度、叶片数和叶面积均显著大于生长在覆沙草地和流沙平地的幼苗的。生长在流动沙丘阴坡上幼苗的植株高度、叶片数目和叶面积介于它们之间 ,主根长度与风蚀低地的没有显著差异 ;(3)风蚀低洼地榆树幼苗根、茎、叶各部分生物量都明显地高于生长在其它 3种生境中幼苗的 ,流动沙丘阴坡上榆树幼苗的生物量还明显高于生长在覆沙草地和流沙平地上的 ,生长在覆沙草地和流沙平地的榆树幼苗的生物量基本上没有差异。该结果说明 ,榆树幼苗在风蚀低地生长最好 ,其次是在流动沙丘阴坡 ,这两种生境可能是浑善达克沙地榆树更新的主要地方。

A comparative researches on the development of elm seedlings in four habitats in the Hunshandak Sandland, Inner Mongolia, China

The temperate semiarid climate occurs in the Hunshandak Sandland, Inner Mongolia, northern China. On the sandy soil, a kind of grassland with patches of elm (Ulmus pumila) trees and some shrubs becomes the sub-climax vegetation. Therefore the landscape looks like somewhat savanna. The elm trees in the grassland play very important roles in reducing the wind velocity and in moderating the harsh habitats. However, more and more of the elm trees died due to over grazing or exposition of roots resulted from soil erosion during the past decades, and few saplings older than two years could be found. In summer of 2001, a great cohort of elm seedlings emerged in the grassland and they grew and survived differently in different types of landform in the following year, but no new seedling emerged in 2002. How does elm tree regenerate and how did the current trees grow up? Elm trees in the grassland grow often in patches or in belts in different kinds of habitats. The trees in a patch or belt seem to be from one or a few cohorts. As landform types with certain ecological conditions are often in patches or belts too and sand dune movement often results in shifts of landform type, the different growth and survival status of the seedlings in different types of landform, and the tree distribution pattern both in space and in tree age elicited a hypothesis that current elm trees might regenerate and grow up from one or a few certain types of landforms, i.e. habitats. To examine the hypothesis, development of the elm seedlings growing in four habitats was comparatively studied in summer of 2002. The four habitats are an eroded low land, a grassland with sandy ground surface, a flat drift sandland and a northern slope of sand dune. The results showed: (1) although number of species per quadrat was not different significantly between the four habitats, coverage of community was least in the grassland with sandy ground surface, and was largest both in the eroded low land and in the flat drift sandland. For the elm seedlings only, the coverage was least in the grassland with sandy ground surface, and was largest in the eroded low land; (2) the seedlings growing in the eroded low land were best, with significant taller shoots, longest main roots, most leaves and largest leaf area, while the seedlings in the grassland with sandy ground surface and in the flat drift sandland were all worst; (3) biomass per seedling growing in eroded lowland was significantly higher than that in the rest three habitats, and biomass per seedling in the sanddune slope was also greater than that in the grasslands with sandy ground surface and with the flat drift sandland. All these suggested that elm seedlings developed best in the habitat of eroded low land, and then better in the northern slope of sanddune than in the habitats of grasslands with sandy ground surface and with flat drift sandland. The eroded low lands with shallow ground water and relative fertile soil, as well as the northern slopes of sanddune with less sunshine and higher soil water content might be the suitable habitats of the elm regeneration in natural conditions.