Patterns of Changes to Woody Vegetation near Resettlement Sites in Semi-arid Northwestern Ethiopia

埃塞俄比亚西北部半干旱地区居民安置点附近木本植被变化规律（英文）

Communal rangelands provide diverse ecosystem services to millions of pastoralists and agro-pastoralists. Resettling destitute communities into hitherto uninhabited communal rangelands and forests, a common practice throughout Sub-Saharan Africa, is a threat to the sustainable use of range and forest land resources. In order to understand the effect of resettlement on a semi-arid woodland in northwestern Ethiopia, satellite imagery of 23 resettlement villages taken over a period of fourteen years, and woody vegetation floristic data for three old resettlements, three new resettlements, two refugee camps and one protected area were analyzed using ANOVA and canonical correspondence analysis（CCA）. The normalized differential vegetation index（NDVI） and canopy cover around all village types decreased with disturbance gradients, while the magnitude of change varied according to the type of settlement. Limited canopy cover was observed in refugee camps and new resettlements, compared to old resettlements and protected areas. Woody vegetation height class showed a J shaped distribution in all sites except refugee camps（RC）, indicating a decline in vegetation. CCA showed that variables like site type, altitude and disturbance gradient significantly affected the diversity of woody species at the different sites. Comparison of individual species responses to disturbances indicated that low fodder value invaders like Dichrostachys cinerea, and many Acacia species were increasing in proportion and coverage at the expense of some multipurpose species including Tamarindus indica, Diospyros mespiliformis, and Pterocarpus lucens. In the absence of regulated vegetation use, resettlements result in a decline in overall vegetation cover and a shift in floristic diversity in favor of invasive species.

公共牧场为数百万牧民和农牧民提供多样化的生态系统服务。将受贫穷困扰的社区居民重新安置到迄今无人居住的社区牧场和森林,是整个非洲撒哈拉以南地区的一种普遍做法,但这对牧场和林地资源的可持续利用构成了威胁。为了解居民的迁移行为对埃塞俄比亚西北部半干旱林地的影响,采用方差分析和典范对应分析(CCA)方法,对埃塞俄比亚西北部半干旱林地的23个安置村14年的卫星影像和3个旧移民点、3个新移民点、2个难民营和1个保护区的木本植物区系数据进行了分析。各类型居民点的归一化植被指数(NDVI)和冠层盖度均随干扰梯度的减小而减小,但变化幅度则因聚落类型而异。与旧的安置区和保护区相比,难民营和新安置区的树冠覆盖有限。除难民营外,所有地点的木本植被高度等级均呈J形分布,表明植被呈下降趋势。CCA结果表明,居民点类型、海拔高度和干扰梯度等变量对不同居民地的木本植物多样性有显著影响。个别物种对干扰的反应比较表明,低饲料价值的入侵物种,如色穗花(Dichrostachys cinerea),许多金合欢属植物种的比例和盖度都在增加,而以牺牲一些多用途的物种为代价,包括罗望子(Tamarindus indica)、非洲黑檀(Diospyros mespiliformis)和光亮紫檀(Pterocarpus lucens)。在没有植被使用管控的情况下,居民的重新定居安置会导致总体植被盖度下降,植物区系多样性发生变化,将为物种的入侵提供机会。