Floristic composition, structure and regeneration status of Riverine forest at Nech Sar National Park of Ethiopia

Abstract

This Study was conducted in Nech Sar National park, Gamo Gofa Zone, Southern Ethiopia for analyzing floristic composition, structure and regeneration status of woody plant species. The floristic composition and population structure of woody plant species were recorded in 76 quadrats, each of which 20 m x 20 m size. Data on species cover abundance, DBH, height and numbers of individuals per species and altitude were recorded from each quadrat. From NNP Riverine Forest 86 vascular plant species, representing 65 genera and 30 families were recorded. The family Fabaceae had the highest number of species (11) followed by Euphorbiaceae each with 7 species, Sapindaceae and Tiliaceae each by 5 species. The four most abundant woody plant species in the forest were Lecaniodiscus fraxinifolus, Trichilia dregeana, Syzygium guineense, Euclea divinorum. Moreover, the five most frequently distributed woody plant species were Lecaniodiscus fraxinifolus, Trichilia dregeana, Syzygium guineense, Euclea divinorum and Maytenus senegalensis. Three communities: Lecaniodiscus fraxinifolius-Trichilia dregeana community, Trichilia dregeana-Syzygium guineense community and Syzygium guineense-Lecaniodiscus fraxinifolius community were recognized, with similarity coefficients of 0.65, indicating that there are moderate similarity among the communities. The Shannon-Wiener diversity and evenness in the forest were 2.92 and 0.68 respectively, indicating high diversity. The matured, sapling and seedling density of species were 1815.8(23.3%), 1344.1(17.2%) and 4635.9(59.5%) stems per ha. The population structure in the forest revealed that there is a need of conservation for communities with poor regeneration status. 1. Introduction Ethiopia is known as the biodiversity hotspot and center of origin and diversification for a significant number of plants, animals and their wild relatives due to its dramatic geological history, broad latitudinal spread and immense altitudinal range. This variety led to the emergence of habitats that are suitable for the evolution and survival of various plants and animal species, which contributes to the overall biodiversity of the country (Tamene et al., 2011). The country flora has approximately 6000-7000 species of higher plants, of which about 780-840 (12-13%) are endemic (Nune et al., 2007). However, the wildlife resources and their natural habitats in Ethiopia are facing various problems due to population pressure, poverty, inappropriate farming systems, climatic changes and other related problems (Samson et al., 2010). Nech Sar National Park (NNP) is one of the protected areas in Ethiopia with diverse component of biological resources which are ecologically and economically important. However, the problems are more intensified and the wildlife population has gradually declined from time to time. Some of the major problems that contribute to the destruction of natural habitats, and hence wildlife in NNP were temporary and permanent settlement, charcoal making, firewood collection, overgrazing, deliberate fire to clear the vegetation for agriculture and selective tree cutting for construction were the main threats in the NNP (Samson et al., 2010; NNP annual report, 2015). This factor is responsible for the decline in their habitat and population density (Workneh, 2009). Arba Minch Natural forest was one of the forests of Nech Sar National Park victimized by these anthropogenic activities as well as environmental factors. Awareness and knowledge on sustainable use and management were very much less (Aramde et al., 2012). According to FAO (2007), the diversity, regeneration status, floristic composition, and vegetation structure are crucial elements to clearly visualize the anthropogenic activities as well as environmental factors affecting the vegetation of an area. Hence, for effective management and conservation of this unique ecosystem of the country, there is an urgent need to develop a sound management and conservation plan, and this, in turn, required detailed baseline information on the ecology and status of the area. Therefore, the objective of this paper is to present the results of the study of the vegetation Diversity and structure of Arba Minch Natural Forest and provide reliable information for the development of appropriate management plan for effective conservation of the park resources. Thus the objectives of the present study are to: (i) compile floristic composition woody plant species, (ii) identify and describe the major plant-community types existing within the study area, (iii) make comparisons of species richness, evenness and diversity among different plant community types,(iv) analyze the species