Biodiversity status of Arabuko Sokoke forest, Kenya

Abstract

Biodiversity monitoring is essential for effective conservation and sustainable management of forests. In recent years, there has been an increasing effort to establish temporary and permanent sample plots explicitly for purposes of biodiversity assessments in forests. In light of this, a study was conducted in Arabuko Sokoke Forest (ASF) to collect baseline data as a benchmark for long term monitoring of changes in flora and fauna due to degradation and climate change. The forest was demarcated into three distinct vegetation types namely; Mixed forest, Brachystegia forest and Cynometra forest, and 27 Permanent Sample Plots (PSPs) established across the vegetation types. Several biodiversity indicators were assessed namely: vegetation (woody plants), edaphic factors, mammals (small and large), birds, and herpertofauna. Impact of socio-economic characteristics and governance on ASF was also evaluated. Tree species richness was slightly high for Brachystegia and Mixed forest but showed slight decline in Cynometra forest and did not change between 2004 and 2015 meaning the floral diversity of the forest has remained relatively intact. High tree species diversity was observed. The soil nutrient levels were significantly different across the different vegetation types. Brachystegia forest had higher mammal species diversity, but less forest specialists than the Cynometra forest. The occupancy and relative abundance of golden-rumped sengi significantly increased in the Cynometra forest. The Sokoke bushy-tailed mongoose had higher occupancy and abundance within the Brachystegia forest. Blue duiker (Philantomba monticola) and golden-rumped sengi occupancy was positively correlated with distance to the forest boundary. Buffaloes and elephants presence was evident in some vegetation zones especially the Mixed forest. Small mammals were mostly restricted to the Cynometra forest type. Birds showed distinctive distributions among the three habitat types, with the Brachystegia woodland emerging as the most preferred. The Cynometra zone had significantly lower abundance followed by Mixed forest. Overall, 36 birds species within 17 families were recorded. Five feeding guilds were registered across the sites. The Brachystegia woodland had the highest (all the five) among the survey sites, while the Cynometra forest had the least feeding guilds represented. Twenty three individuals of herpes were recorded comprising of 9 species. Reptiles were represented by 3 families and amphibians by 2 families. Lizards’ species followed by snakes were the most diverse and abundant. Speke’s Sand Lizard (Heliobolus spekii) was only found in Brachystegia woodland. Herpertofauna diversity was least in Cynometra forest type. The quantity of forest products extracted had declined over the years. This decline was mainly attributed to low demand for forest products especially poles and posts resulting from poor performance of the local economy. Besides, forest governance and management has deteriorated from the period before colonization era to date. The deterioration was attributed to unlawful means of accessing resources, poverty, and lack of incentives for communities to meaningfully participate in forest management. Proposed mitigation measures were: to ensure sensitization and awareness of stakeholders; and provision of incentives to enable communities effectively participate in forest management