Assessing removal methods for controlling Dichrostachys cinerea encroachment and their impacts on plant communities in an East- African savannah ecosystem

Questions: Woody plant encroachment is known to adversely affect the biodiversity and functioning of savannah ecosystems, yet removal strategies have been shown to have variable success. Here, we evaluated the effectiveness of three woody removal methods or treatments for controlling the leguminous thorny shrub Dichrostachys cinerea, and assessed plant community responses following removal.Location: Savannah plains of Nech Sar National Park, South-Ethiopian rift valley.Methods: Based on a total of seventy-two 10 m x 10 m experimental plots spread across six blocks, we carried out: (a) stump burning; (b) stump application with glyphosate herbicide; and (c) mechanical uprooting on D. cinerea, and monitored the number, height, and thickness of resprouts and the number of resprouting stumps for two consecutive years. In addition, we surveyed all vascular plant species per plot for each removal method and control.Results: We found that the uprooting treatment resulted in a higher number of resprouting stumps and lower number of resprouts, and a smaller resprout height and diameter. The fire treatment showed the greatest reduction in the number of resprouting stumps and resprouts, whereas glyphosate treatment showed intermediate results although resprout height and diameter were significantly greater compared with the uprooting treatment. Whereas plant species richness and diversity were higher in the fire treatment, they were adversely affected in the uprooting treatment.Conclusion: Our results demonstrate that none of the woody removal methods were effective enough to completely eradicate D. cinerea from the field trials after only one intervention, suggesting the need for follow-up management actions considering their impacts on both woody encroachment and biodiversity restoration.