RESPONSE OF HERBACEOUS VEGETATION TO WOODY PLANT SPECIES IN THE RANGELANDS OF EASTERN ETHIOPIA

Abstract

In the lowlands of arid and semiarid rangelands woody plants plays an important role in soil fertility maintenance, providing food, medicine, cosmetics, fodder, fuel wood and pesticides. A better understanding of the interaction of woody plants on their immediate environment is needed to guide optimum management of native vegetation in the production landscapes. However, the response of herbaceous vegetation to woody plant species remains poorly understood. This study evaluates the impact of two dominant woody plant species (Acacia senegal and Balanite aegyptica) on herbaceous vegetation in rangelands of eastern Ethiopia. Eighteen trees of relatively the same diameter at breast height were selected to study the effect of the tree on herbaceous vegetation. Vegetation sample data were collected from under canopy and open areas, and analysed for herbaceous vegetation parameters using two ways ANOVA. The herbaceous vegetation parameters under both woody plant species was significantly higher especially with regard to dry matter (101.3±0.97g/m2), basal cover (65.02±0.7%) and species richness (6.9±0.1211 no. species/m2) than the open grassland with dry matter (74.2±0.72g/m2), basal cover (50.53±0.67%) and species richness (5.3±0.11 no. species/m2). The species composition of herbaceous species also showed significant improvements under woody plant canopy with regard to percentage composition of perennial grasses (0.40%) than the open grassland with percentage composition of perennial grasses (0.27%). The positive effect woody plant presence can be also ascribed to some understory species such as Cenchrus ciliaris, Panicum maximum and Eragrostis papposa which have a good pastoral value, grow better under woody plants. Presence of woody plants facilitates the establishment of more palatable herbaceous vegetation under unfavorable climatic conditions that characterize these environments. Therefore, this tree has a significant effect on herbaceous vegetation improvement in resource poor rangelands and as a result, it is important to retain scattered A. senegal and B. aegyptica plants in the rangelands of eastern Ethiopia.