Vegetation composition and dynamics along degradation gradient of Kiang'ombe hill forest in the drylands of Kenya.

Abstract

Kiang'ombe hilltop forest is overexploited for fuel wood, charcoal, timber and non-wood forest products, thus threatening its biodiversity conservation role. The extent of forest degradation is not yet quantified and this impedes rehabilitation interventions. This study was conducted to evaluate the status of Kiang'ombe forest resources to initiate rehabilitation interventions and to support sustainable forest management. Remote sensing and geographic information systems (GIS) were used to determine trends of spatial and temporal vegetation changes over 25 years. Image analysis revealed high, moderate and low categories of forest degradation over the assessment period. Thirty two nested sample plots were used for vegetation inventory in the three degradation gradient clusters. Additional data was obtained from local informants through focused discussions and field observations. A total of 155 plant species belonging to 58 families were identified. Shannon Weiner diversity index of seedling and sapling were higher in low and moderate than in high degraded areas. Based on species importance values, the candidate trees for rehabilitation of degraded areas were Croton macrostachyus, Acacia hockii, Combretum molle and Faurea saligna whereas Enteropogon macrostachys, Cymbopogon sp., Eragrostis superba and Hyparrhenia rufa were the most suitable grass species for reseeding expansive glades. The recommended rehabilitation techniques are enrichment tree planting in water catchments areas, enhancing natural regeneration through protection and grazing management, gully healing at the hill slopes and establishment of woodlots plantations and boundary planting in the surrounding farmlands.     Key words: Hilltop forest, geographic information systems (GIS), vegetation inventory, rehabilitation techniques.