草地灌丛化对植被与土壤的影响

Influences of Bush Encroachment on Vegetation and Soil

位于东非高原低海拔区的埃塞俄比亚博拉娜区草地正遭受着灌丛化的威胁。本文将博拉娜区灌丛化草地按灌木盖度分成3个等级,研究不同灌丛化程度草地植被及土壤理化性质的差异。结果表明:随灌丛化程度增加,灌木冠幅和种类增加,高度先增加后降低,密度先降低后增加;草本植物的盖度、高度、优势种盖度下降,但优势种有所增加;含水量、黏粒含量下降,其中轻度灌丛化草地(灌木盖度40%~60%)含水量达22.36%,容重和紧实度先下降后上升,中度灌丛化草地(灌木盖度在60%~80%)容重达1.23 g·cm^(-3);有机质、全磷、速效磷、pH先增加后降低,在中度灌丛化草地分别为4.73%、0.73 g·kg^(-1)、16.86 mg·kg^(-1)、8.19;全氮和无机氮含量增加,在重度灌丛化草地(灌木盖度>80%)高达1.85 g·kg^(-1)、12.29 mg·kg^(-1)。

There is undergoing a bush encroachment in Borana,Southern Ethiopia,in lowland of east Africa. In this paper,the bush-encroached grassland is divided into three levels by the shrub coverage so as to analyze the influence of bush encroachment on herbaceous vegetation and soil properties in the bush-encroached grassland with different grades. The results showed that,with the increase of brush encroachment grade,the canopy and variety of bushes were increased,the height was increased at first and then reduced,and the density was decreased at first and then increased; the herbaceous vegetation coverage and height as well as the coverage of dominant species were increased to some extent; soil moisture content and clay content were decreased,in which the soil moisture content in slightly bush-encroached grassland（ shrub coverage was 40%-60%） was as high as 22. 36%,and the soil bulk density and compactness were reduced at first and then increased. In moderately bush-encroached grassland（ shrub coverage was 60%-80%）,the soil bulk density was 1. 23 g·cm^-3. The soil organic matter content,TP,AP and pH value were increased at first and then decreased,and these values in the moderately bush-encroached grassland were 4. 73%,0. 73 g·kg^-1,16. 86 mg·kg^-1and 8. 19 respectively. The contents of total nitrogen and inorganic nitrogen were increased,and they were 1. 85 g · kg^-1and 12. 29 mg · kg^-1respectively in seriously brush-encroached grassland（ shrub coverage 〉80%）.