沙漠植物分层侧影与积沙成丘的关系

选用民勤沙区常见的几种固沙植物,在民勤西沙窝沙漠边缘设置了108个植物和沙堆样方,通过对不同植物的分层侧影宽度、分层侧影面积和侧影中心等指标的测定和对比分析,得出如下结果:1)可积沙成丘植物的侧影为三角形或柱形,即由地面向上侧影宽度变小,侧影中心在近地面30 cm高度内,具备这一条件的植物为丛生灌木。而不能积沙成丘的植物侧影为菱形,侧影中心距地面高度在30 cm以上。2)风沙流以及沙尘暴中的沙粒主要集中在近地表0—30 cm高度内流动,这便是植物侧影越低,越易积沙成丘的重要原因之一。3)沙埋后茎秆能产生不定根的植物可形成高于植株几倍至数十倍高度的沙堆/沙丘,而不具备这一属性的植物,有些虽然能形成沙堆,但沙堆受植物高度限制,即沙堆高度不会超过植株高度。4)侧影面积大小是反映植物防风固沙功能的一个十分重要的指标,能积沙成丘是植物阻固流沙的物质体现,形成的沙堆越高大则表明植物阻固流沙的功能越强,但不能积沙成丘的植物如梭梭、沙拐枣、沙蒿等也是具有一定防风阻沙效果的。

Initial research on the relationship between sand-mound formation and the layered silhouette of desert plants

Some desert plants can accumulate sand into mounds and form nabkhas, whereas some cannot. The reason for the difference is unknown. To understand the difference, we selected several common sand-fixing plants in the Minqin desert area and collected 108 samples of these plants and sand from the mounds along the fringe of Minqin Xishawo. We measured and compared the layered silhouette width, the layered silhouette area, and the silhouette center of different plants. The results showed 1) the silhouette of plants that form sand mounds are triangular or cylindrical, which means the width of the silhouette becomes smaller from the ground to the top, and the silhouette center is within 30 cm from the ground. Plants with this characteristic are clumping shrubs. The silhouettes of plants that do not form sand mounds were diamond-shaped, and the silhouette center was 30 cm or more from the ground. 2) Sand particles in aeolian-sand flow and sandstorm flow were primarily concentrated within 0-30 cm above the surface, which was an important reason why the lower the plant silhouette, the more easily the nabkhas were formed. 3) Plants with stems that can produce adventitious roots after sand burial can form sand mounds or dunes, which are several to dozens of times higher than the plant itself. Although some plants do not produce adventitious root after sand burial, they can nonetheless form sand mounds or dunes; however, the height of the sand mound or dune will not be higher than the plant itself because of the limitation of the height of the plant itself. 4) The size of the silhouette was an important indicator that reflected its function as a windbreak and sand-fixing properties of the plant. The plant''s ability to accumulate sand into a mound was the manifestation of the function of stopping and fixing mobile sand. Higher sand mounds reflected a stronger function in stopping and fixing mobile sand by the plant. However, plants that do not form sand mounds or dunes, such as Haloxylon ammodendron, Calligonum mongolicum and Artemisia arenaria etc., also can function in stopping and fixing mobile sands.