Woody species dynamics in Sheka Forest Biosphere Reserve, Southwest Ethiopia

Abstract

Understanding the dynamics of woody species diversity is the foundation for designing sustainable biodiversity management strategies. Despite an extensive history of cross-sectional ecological studies, scientific gen on the dynamics of woody species diversity over time and space is rare and mostly unexplored in the last remaining Eastern Afromontane Forests. This study aimed to examine the spatial and temporal dynamics of woody species composition, structure, and diversity in the Sheka Forest Biosphere Reserve (SFBR). Data were collected from a total of 43 permanent plots with a dimension of 10 m × 50 m that were laid along the altitudinal gradient. In both 2000 and 2021, the same permanent plots were used and the same approach was followed. Diversity indices and Wilcoxon paired-sample test were employed for the comparison of changes. One hundred one woody species that belong to 84 genera and 41 families and 62 woody species that belong to 54 genera and 32 families were recorded in 2000 and 2021, respectively. During the present study, 47 woody species from the 2000 inventory list including three endemics were not encountered, while eight new species were recorded. The aggregated density and total basal area of woody species decreased from 2590 ± 536 ha−1 to 2454 ± 300 ha−1, and 101.3 m2ha−1 to 72m2ha−1, respectively. The dominant woody species was Ficus sur in 2000, while it was shifted to Coffea arabica in 2021. Woody species richness, evenness, and diversity significantly reduced during the study period. In the mid and lower altitudes with lower slope gradients, where settlement and agricultural expansion were prevalent, the greatest decline in woody species richness, diversity, and evenness, and highest turnover were recorded. Unsustainable use for construction, energy production, creation of job opportunities (income generation), as well as the conversion of forestland to farmland resulted in the rapid decline and massive turnover of woody species diversity. It is important to develop and execute comprehensive sustainable forest management strategies, which include diversification of energy sources and use of energy-saving technologies, strengthening tree planting and management practices for household use and income generation, and diversification of eco-friendly livelihood options. The conservation of endemic and priority species is indispensable to maintaining ecosystem integrity and species diversity.