腾格里沙漠南缘固定沙丘活化斑的空间分布特征

Spatial distribution of sandy patches in fixed dunes in the Tengger Desert,Northern China

沿腾格里沙漠东南缘包兰铁路沿线中卫-干塘段设置3条宽度为1 km且垂直于路基的样带,调查距路缘不同距离植被及活化斑的数量特征,以揭示铁路沿线人工植被区内活化斑的空间分布特征及其影响因素.结果表明:随着路缘距离的增加,植物种数呈直线下降的趋势;灌木植物的盖度在路缘处为最大值30%,当路缘距离>220 m时,灌木植物的盖度下降至最小5%;草本植物盖度则随着路缘距离的增加呈先增加后减少的趋势;该地区活化斑以小尺度斑块为主,分布于距离路基150~200 m,有90%以上的斑块直径小于10 m,平均斑块直径5.8 m.平均活化斑块面积及周长亦随路缘距离的增加而增加,坡度20°~30°斑块数量最大;对于沙丘不同部位而言,活化斑主要分布在丘顶和迎风坡,二者占到了活化斑总数量的63%.不同距离、坡度和地形的圆环度指数、扩展度指数和方形指数均>1,说明活化斑的形状明显偏离于圆形和方形,为不规则形,且异质性较大.相关分析表明,活化斑的平均斑块面积和距离呈极显著的正相关关系,活化斑的数量主要受坡度和灌木盖度的影响,活化斑的平均周长亦主要受制于坡度,并呈极显著的正相关关系,其次是灌木盖度、植被种数、距离和草本盖度.

Based on the data from field investigation into three intercepting 1 km transects along the Zhongwei-Gantang section of the Baotou-Lanzhou railway,the vegetation species composition and the spatial distribution of sandy patches were analyzed.The results showed that,with increasing distance from the road edge,the species number declined,the coverage of shrub was 30%at the road edge and then decreased to about 10%at 100 meters from the edge.When the distance was greater than 220 m,the coverage of shrub dropped to a minimum of 5%;herbaceous plants coverage increased first and then decreased with the increase of road distance.The area of active sandy patches was small,more than 90%of the patch diameter was less than 10 m and the average patch diameter was 5.8 m.The numbers of sandy patches were largest in 150-200 m from the road edge with the slops ranging from 20°-30°.The areas and circumferences of sandy patches were increased with increasing distance from the road edge.For the different parts of the sand dunes,sandy patches were mainly distributed in the top and windward side,which accounted for 63%.The value of circularity index,development index and square index at different distance,slope and terrain were greater than 1,indicating that the shapes of sandy patches were irregular and obviously deviated from both circle and squire and closely correlated with the heterogeneity of our research areas.Correlation analysis showed that the number of sandy patches was mainly affected by the slope and shrub cover,the area of sandy patches was significantly positively correlated with distance,and the circumference of sandy patches was mainly determined by the slope,followed by the shrub cover,vegetation number,distance and herbaceous cover.