Composition and distribution of indigenous trees and shrubs as possible criteria for indicating adapted species in semi-arid rangelands

Abstract

This study assessed the composition and natural distribution of indigenous trees and shrubs as possible criteria for selecting suitable species for rehabilitation of degraded sites in semi-arid rangelands. Study sites were identified at Nthangu, Kathonzweni and Kibwezi forests of Makueni County, Kenya using existing vegetation, agro-climatic maps and Landsat imageries. The sites had mean annual rainfalls of 974mm, 700mm and 616mm, respectively, and moisture indices of 49%, 35% and 32%. Data were collected by establishing sample plots and assessing species counts and diameters at breast height (DBH). Basal area, relative dominance, relative abundance, relative frequency and important value indices (IVIs) were computed for individual families and species at each site. The number of families, genera and species declined from Nthangu (33, 60, 77) through Kibwezi (30, 48, 70) to Kathonzweni (28, 42, 69). Corresponding mean basal areas were 16.7m(2)ha(-1), 76.8m(2)ha(-1) and 19.3m(2)ha(-1). The families Combretaceae, Burseraceae and Mimosaceae were the most important and widely distributed. Based on ecological importance values, candidate species for rehabilitation of degraded sites at Nthangu, Kathonzweni and Kibwezi were Combretum molle and Acacia hockii; Combretum collinum, Commiphora campestris and Acacia tortilis; and Commiphora africana and A.tortilis, respectively.