Data Sheet 1_How much to cut? Finding an optimal thinning intensity of encroaching woody species for the herbaceous community in an East African savanna.zip

Globally, bush encroachment poses a great threat to the conservation of biodiversity and rangeland productivity. However, control methods of encroaching woody species have rarely been experimentally quantified. We assessed the impact of tree thinning intensities on tree mortality, and the herbaceous community in Borana rangelands, an Ethiopian savannah ecosystem. At two 1.4 ha areas of mono-specific Vachellia drepanolobium stands, we set up 20 m x 10 m experimental plots with four tree-thinning treatments (0%, 33%, 67%, and 100% tree removal), with three replications in a randomized complete block design (RCBD) across two sites. The 0% plot was left uncleared and used as control. Over two growing periods, we monitored resulting tree mortality, coppicing, seedling mortality, and recruitment as well as herbaceous layer attributes (diversity, biomass) and the rangeland conditions. Tree thinning intensity significantly increased abundance of the dominant desirable grass species. Total herbaceous and grass species richness, diversity and biomass were significantly improved under high (100%) and moderate (67%) tree removal intensity. We conclude that tree thinning at moderate intensity (67%) was most effective in enhancing mortality of encroached trees, and improving grass diversity, and herbaceous biomass. We stress that effective tree thinning requires post-thinning management and repeated bush control measures. Our findings contribute to development of recommendations on controlling bush encroachment, species restoration, and rangeland productivity in Ethiopian rangelands.

全球范围内，灌丛入侵对生物多样性保护与牧场生产力均构成严重威胁。然而，针对入侵木本物种的防控手段鲜有经过实验量化的研究。本研究以埃塞俄比亚博拉拉牧场（Borana rangelands）这一热带稀树草原生态系统为研究对象，评估了树木疏伐强度对树木死亡率及草本群落的影响。研究选取两处面积各为1.4公顷的单优弯刺金合欢（Vachellia drepanolobium）林分，在两个样地采用随机完全区组设计（randomized complete block design, RCBD）设置了20m×10m的实验样方，包含4种疏伐处理（0%、33%、67%和100%伐树），每种处理设置3次重复，其中0%伐树样方未进行清理，作为对照。在两个生长季内，本研究监测了树木死亡率、萌蘖情况、幼苗死亡率、幼苗更新情况，以及草本层特征（物种多样性、生物量）和牧场状况。结果表明，树木疏伐强度显著提升了优势优良禾草物种的多度。在高伐树强度（100%）和中度伐树强度（67%）处理下，草本植物总物种丰富度、禾草物种丰富度、多样性及生物量均得到显著提升。本研究结论显示，采用中度疏伐强度（67%）可最为有效地提升入侵树木的死亡率，并改善禾草多样性与草本层生物量。本研究强调，有效的树木疏伐需配合疏后管理与重复灌丛防控措施。本研究结果可为埃塞俄比亚牧场的灌丛入侵防控、物种恢复及牧场生产力提升提供决策参考依据。