内蒙古半干旱地区沙质过牧草地的沙漠化过程

为了掌握我国北方半干旱地区沙质放牧草地的沙漠化过程，在内蒙古东部的科尔沁沙地进行了为期5年的放牧试验。结果表明，在牧草利用率为70％的过牧条件下，草地植被盖度、高度、个体大小和根量急剧降低，第5年分别只有10.1％、1.0cm、2.5cm^3／株和18.7g/m^2（0－30cm土层内），是禁牧区的12.0％．3.02％．0.86％和22.1％。同时，家畜觅食活动增加，对草地践踏作用增强，如第5年其单位面积的蹄印6数和每只羊单位面积的蹄印数达到36.4n/m^2和8.5n/m^2，分别是轻牧区的9.6倍和8.25倍，土壤紧实度是禁牧区的3.75倍。植被盖度、高度、根量和植物个体普遍降低，家畜喜食植物首先从草地中退出后，草地开始出现小块裸斑，随着过牧的继续，这种裸斑迅速增加和扩大，使之相互连接成为大片裸地，如试验当年过牧区裸斑数仅为19个，而且73.7％≤2.5m的裸斑，到第3年裸斑数迅速增至358个，＞2.5m的裸斑比例从26.3％增加到31.3％，裸地率由1.8％增加到35.8％，第5年裸斑平均长度由2.4m增加到4.1m，＞2.6m的裸斑比例增至45.7％，裸地率达到了51.6％。当地面出现裸斑后，即使冬季不进行放牧，在风力的作用下草地中的裸地面积也会自然扩大，如第5年秋季过牧区的裸地率为51.6％，到第6年春季自然扩展到71.6％。裸地出现以后，冬春季在风力作用下地面迅速出现风蚀，过牧区第3年70％的测点发生风蚀，平均风蚀深度8.5cm，第5年90％的测点发生风蚀，平均风蚀深度25cm，最大风蚀深度90cm，地面呈现出凹凸不平的风沙地貌。研究结果表明，试验期间夏季放牧啃食对地表裸露的贡献率为41.3％，而冬春季节土壤风蚀对地表裸露的贡献率高达58.7％，这说明在内蒙古半干旱风沙区地表一旦裸露，马上就会因风蚀而迅速扩大。

Sand Ddesertification Processes of Over-grazing Pasture in Inner Mongolia

To study desertification processes of sand grassland in semi-arid area, grazing experiment for 5 years was carried out in Horqin Sand Land, Inner Mongolia. The results shown that vegetation height, cover, individual size and root mass reduced sharply when grazing rate of grass was higher 70%, which were 10.1%, 1cm, 2.5cm 3 and 18.7g/m 2 separately at 5th year, and just were 12.0%?3.02%?0.86% and 22.1% of that in the ungrazing plot. At same time, the animal activities and trample action in grassland was increased, hoof print numbers in grassland were 36.4n/m 2 and 8.5n/m 2 sheep, and were 9.6 times and 8.25 times of that in light grazing plot respectively, but soil hardness was 3.75 times of ungrazing plot. As overgrazing continued, small bare spots appeared in grassland while plant height and cover and individual size reduced generally, and the bare spots was increased and enlarged rapidly, and was mutually connected to greaterbare plots. For example, there was 19 bare plots and 73.7% of bare plots was smaller than 2.5m at first year in overgrazing plot, but bare plot number increased to 358, and the rate of >2.5m bare plots and bare land rate increased respectively from 26.3% to 31.3% and from 1.8% to35.8% at third year, which average length of bare plots increased from 2.4m to 4.1m, and the rate of >2.5m bare plotsand bare land rate increased respectively to 45.7% and 51.6% at 5th . Bare land area affected wind can be naturally spread even no grazing in winter and spring after bare land appeared in grassland. For example, bare land rate was 51.6% at5th autumn and was 71.6% at 6th spring. Wind erosion appeared rapidly under wind action after ground surface baring. 90% measured points appeared wind erosion and average depth of wind erosion was 25cm and the greatest depth 90cm at 5th under overgrazing ,and wind-sand landscape had appeared. Contributing rate of animal grazing to ground surface baring in summer was 41.3% and contributing rate of wind erosion in winter and spring was 58.7%.