The effects of bush control methods on encroaching woody plants in terms of die-off and survival in Borana rangelands, southern Ethiopia

A study on the effect of bush control methods on encroaching woody species, namelyAcacia drepanolobium,Acacia melliferaandAcacia reficienswas conducted for a 2 years' time. A 3 ha of land was divided into two plots. Each replication with an area of 300 m x 50 m was again sub-divided into six plots (each 50 m x 50 m) to accommodate six treatments. Bush control treatments were assigned randomly to the plots and replicated two times across sites of similar topography. During the post-treatment period, responses of woody species to different treatments in terms of mortality and coppicing were monitored. Data was analysed using R software and Tukey's studentized range tests for comparisons of means. The applied treatments significantly influenced (P < 0.05) encroaching woody species. The finding showed that five out of the six bush control treatments greatly promoted woody mortality, however with species-specific differences. The stem-burning, tree cutting with fire-browse combination, cutting and fire, cutting and browsing, and cutting treatments greatly increased species mortality compared to the control treatment. Responses due to treatment effect also varied significantly (P < 0.05) among encroaching woody species. Accordingly, mortality was higher inA. reficiensthan in the other two species, indicating thatA. reficiensis greatly susceptible to the applied treatments. The significant finding was that woody species exhibited greater mortality in response to selective cutting/thinning and post-management techniques. Post-thinning management measures would sustain savanna ecology, if implemented at certain intervals.