Effect of Human Activities on Floristic Composition and Vegetation Structure of Sorga Water Shade Forest, Nekemte, Western Ethiopia

Advisor: Fekadu Gurmessa (Ph. D.) Human activities have been altering natural environments since prehistoric times. One of the most significant impacts is the conversion of forests to other land uses, resulting in reduced species diversity and disrupted vegetation structure. This study aimed to assess plant species diversity and the effects of human activities on floristic composition and vegetation structure in the Sorga Water Shade Forest (hereafter referred to as SWSF). A total of 39 systematically placed plots (20 m × 20 m each) were established along transects extending from Sorga Lake to the forest periphery. Data were collected September 2024. Vegetation and environmental variables were recorded in each plot, and plant specimens were identified using the Flora of Ethiopia and Eritrea. Human disturbance levels were evaluated using a subjective scale, and elderly informants were interviewed to gain insights into historical vegetation changes and threats to forest biodiversity. Data were analyzed using agglomerative hierarchical clustering and Canonical Correspondence Analysis (CCA) in R (version 3.1.1). Shannon-Wiener diversity and evenness indices were computed to assess species diversity. Sørensen’s similarity coefficient was used to compare floristic similarities among plant communities and with other forests in Ethiopia. In total, 85 vascular plant species representing 78 genera and 52 families were recorded, including three species endemics to the region. SWSF showed strong floristic affinity with Komto and Gendo forests. Cluster analysis revealed four plant community types. Ordination indicated that anthropogenic disturbance significantly influenced species composition and distribution. Importance Value Index (IVI) analysis identified Syzygium guineense, Cupressus lusitanica, Byttneria catalpitiolata, and Croton macrostachyus as dominant tree species. Tree size class distribution exhibited an inverted J-shape, indicating ongoing regeneration, though larger size classes were dominated by few species, suggesting selective logging pressure. The study concludes that sustainable and multifaceted conservation strategies are urgently needed to mitigate human impact and preserve the ecological integrity of SWSF.
Keywords/Phrases: Anthropogenic impact, SWSF, Species diversity, Vegetation structure