HERBACEOUS SPECIES DIVERSITY, BIOMASS PRODUCTION AND SELECTED SOIL PHYSICOCHEMICAL PROPERTIES UNDER TREE CANOPIES OF PARKLAND AGROFORESTRY SYSTEM IN GUDURU DISTRICT, HORRO GUDURU WOLLEGA ZONE, WESTERN OROMIA, ETHIOPIA

Abstract

Indigenous tree species have an essential value in ecosystems however, most tree planting initiatives have promoted exotic species because of less understanding on their actual potential. This study was conducted in grazing parkland agroforestry system in Guduru district, Western Ethiopia to examine the effect of three indigenous tree species; Acacia abyssinica, Croton macrostachyus, Ficus sur and their canopy cover on herbaceous diversity, biomass production and selected soil physicochemical properties. Three relatively similar trees per each of the species were selected for this study. A quadrat of 0.5mX0.5m (0.25m2) was laid out at different distances from tree trunk. Shannon diversity index was used to estimate the diversity of herbaceous species under and outside canopy of tree species. A Total of twenty seven samples (one hundred and eight subsamples) were laid out to collect data for herbaceous diversity, biomass production and soil samples. Two-way analysis of variance (ANOVA) using General Linear Model (GLM) procedure in an arrangement of randomized complete block design was applied with SAS (version 9.1) software to test the differences between the investigated parameters as factor of tree species and canopy cover. When significant differences were detected means were separated using LSD at 5% level of significance. A total of thirty one herbaceous species that belonged to twelve families were identified. The highest herbaceous species richness, diversity and biomass production (1.75, 2.21, 117.6g) were obtained outside the tree canopy. Generally, lower herbaceous richness, diversity and biomass production were observed under tree canopy which might be because of densed structure of tree canopies and lack of appropriate silvicultural operations. A significant effect of tree canopy on selected soil physicochemical parameters might be due to the nutrient addition of trees through their root systems in association with soil microorganisms and litterfalls decomposition