民勤沙区植被退化与年际降水量关系的定位研究

民勤沙区荒漠植物盖度随年际降水量变化明显,植被在随年际降水量变化的波动中退化。在一般年份,白刺、梭梭、沙蒿等灌木上部发生枯梢,在降水量偏少或分布异常年份会整株枯死,所以有的年份植被盖度和灌木高度反而会降低。不同植被群落分布的地貌条件和土壤条件有较大差异:白刺以白刺沙丘的形式存在,白刺沙丘0～30cm土壤含水率在1.4%～2.0%之间;膜果麻黄仅分布在粘砾石质滩地上,0～30cm土壤含水率<0.8%;沙蒿分布在低缓的半固定沙丘、流动沙丘和覆沙滩地上,0～30cm土壤含水率在0.9%～1.7%之间。植物通过土壤水分变化对降水作出反应,土壤水分条件对降水的反应受土壤颗粒的影响,细砂粒对降水反应灵敏。优势种植物高度与7月下旬～9月下旬的降水量之间存在较大的正相关;草本植物平均盖度与7月下旬～9月下旬和5月下旬～7月下旬期间的降水量之间存在较大的正相关。全年降水量主要影响植被总盖度。5月下旬～7月下旬的降水量对植被的影响较全年降水量更为明显。

Position Study of the Relations between Vegetation Degeneration and Annual Rainfall in the Sand Region of Minqinxian County

In the sand regions of the Minqianxian County,the coverage of desert plants remarkably varies with year-by-year rainfall fluctuation in which the vegetations degenerate.Kraurosis takes place on the top parts of upper Nitraria tangutorum,Haloxylon ammodendron,Artemisia arenaria shoots in the years with normal rainfalls,kraurosis takes a grip on the whole plants in the years with slightly lower rainfall or irregularly-distributed rainfall,and thus the vegetation coverage and shrub heights decline in some years.The landforms and soils occupied by different vegetation communities differe relatively greatly, Nitraria tangutorum growing on sand dunes whose 0~30 cm soil has a water content of 1.4%~2.0%, Ephedra przewaskii only distributing on clay and rudaceous beachlands whose water content is less than 0.8% in 0~30 cm soil, Aretemisia arenaria taking low semi-fixed dunes with mild slope,shifting dunes and sand-covered beachlands whose water content is 0.9%~1.7% in 0~30 cm soil.Plants response to rainfall through soil moisture and the response of soil moisture to rainfall depend on soil particles,thin sand particles presenting capable of sensitively responding to rainfall.The heights of the dominant plant species relatively strongly and positively correlate with the rainfall between the later ten days of July and the later ten days of September.The coverage of herbaceous plants relatively strongly and positively correlates with the rainfalls between the later ten days of July and the later ten days of September,and between the later ten days of May and the later ten days of July.The annual rainfall mainly affects the total vegetation coverage.The rainfall between the later ten days of May and the later ten days of July affects the vegetation coverage more than the annual rainfall does.