The spread of woody plant encroachment is a major concern as it adversely affects herbaceous plant community composition in a savanna ecosystem. Assessing the canopy effects of co-occurring encroaching and non-encroaching woody plant species on the understory herbaceous vegetation biomass and the soil nutrient status can improve our understandings of the link between biological invasions and herbaceous plant community ecology. We examined the canopy and adjacent inter-canopy effects of encroaching and non-encroaching Vachellia species which was previously known as Acacia on herbaceous vegetation biomass in Southern Ethiopia. A total of 12 encroaching (Vachellia drepanolobium) and 12 non-encroaching (Vachellia tortilis) tree species were selected both at an upland and a bottomland site. A 1 m × 1 m quadrat was used to investigate the canopy effects of individual tree species and inter-canopy habitats on herbaceous vegetation biomass. Soil samples were collected under the canopy of selected tree species and the adjacent inter-canopy habitat at a depth of 0–10 cm and 10–20 cm both at the upland and bottomland site. With fixed effect ANOVA, we evaluated the effects of landforms (upland or bottomland), tree species (Vachellia drepanolobium or Vachellia tortilis) and habitats (canopy or inter-canopy habitat) on total herbaceous biomass, perennial herbaceous species biomass and annual herbaceous species biomass. There was no significant (P > 0.05) difference between the canopy and inter-canopy habitat of V. drepanolobium and V. tortilis in terms of the total herbaceous biomass and annual herbaceous vegetation at the bottomland position. The canopy of V. drepanolobium had a negative effect on the biomass production of herbaceous perennial species both at the bottomland and upland site. On the contrary, the canopy of V. tortilis had a significantly positive (P < 0.05) effect on the biomass production of herbaceous perennial plants at the bottomland site. Generally, more soil organic matter accumulation was recorded under the canopy of V. tortilis than it was either under the canopy of V. drepanolobium or in the open savanna grasslands. Our findings indicated that encroaching tree species canopy and co-occurring non-encroaching tree species canopy had a predominantly different influence on herbaceous vegetation biomass. It seemed that encroaching tree species in savannas had a high acquisition and competition for resources. The findings can help improve our understanding on the herbaceous biomass predictions of different life forms in a community of encroached grasslands and non-encroached grasslands in southern Ethiopia.

木本植物入侵的扩散是一个主要问题，因为它对热带稀树草原生态系统中的草本植物群落组成产生不利影响。评估同时侵害和非侵害的木本植物物种对林下草本植物生物量和土壤养分状况的冠层效应可以增进我们对生物入侵与草本植物群落生态之间联系的理解。我们研究了侵略和非侵略的Vachellia物种（以前被称为相思树）对埃塞俄比亚南部草本植物生物量的冠层和相邻冠层之间的影响。共有12种侵害性（Vachellia drepanolobium）和12种非侵害性（Vachellia tortilis）在高地和低地都选择了树种。使用1 m×1 m的方方动物调查单个树种和冠层间生境对草本植被生物量的冠层效应。在选定的树种的树冠下和相邻的树冠间生境下收集土壤样品，其高地和低地都在0–10 cm和10–20 cm的深度处。利用固定效应方差分析，我们评估了地貌（高地或低地），树种（Vachellia drepanolobium或Vachellia tortilis）和栖息地（冠层或冠层间生境）对总草木生物量，多年生草木生物量和一年生草木生物量的影响。 。没有显着性（P > 0.05）在底地位置，drepanolobium和V. tortilis的冠层和冠层间生境之间的差异包括总草木生物量和一年生草木植被。底栖葡萄球菌的冠层对低地和高地地点多年生草本植物的生物量产生不利影响。相反，曲折弧菌冠层对 底地多年生草本多年生植物的生物量产生了显着的正向影响（P <0.05）。一般情况下，更多的土壤有机质积累的树冠下记录的五tortilis比它要么的树冠下五drepanolobium或在开阔的稀树草原上。我们的研究结果表明，侵蚀性树冠和同时存在的非侵害性树冠对草本植物生物量的影响主要不同。似乎稀树草原上入侵的树种对资源的获取和竞争很高。这些发现可以帮助我们加深对埃塞俄比亚南部被侵蚀草地和非被侵蚀草地社区不同生命形式的草本生物量预测的理解。