Diversity and regeneration status of native woody plants species under Eucalyptus and Cupressus plantation forests around Jimma town, Oromia Regional State, Southwest Ethiopia

Abstract

Plantation forests are man-made forest ecosystems, established by planting or seeding, which helps in the process of afforestation and reforestation. Native plants are plants that have been growing in a particular habitat and region, typically for thousands of years or longer. The main aim of this research was to assess the effects of Eucalyptus and Cupressus plantations on native woody plants species diversity and compare natural regeneration status under those plantation forests. The study was conducted around Jimma town. A plot sampling method was used to gather vegetation data from quadrats measuring 20 m × 20 m at intervals along a 100 m transect line. The collected plant specimens’ identification was carried out both in the field and later in the Herbarium. The Shannon diversity (H') and evenness (E') indices were calculated as a measure to incorporate species richness and diversity. The regeneration status of the two forest stands was also assessed by computing density ratios between seedlings and saplings and trees individuals. The height classes for seedlings (< 0.5 m), saplings (0.5 m – 2 m) and trees (> 2 m) was used to categorize plants height structure. Those Species which possess high number of individuals in the lower height classes, particularly in the first class, were considered to have good regeneration potential. In total, 42 species of native trees and shrubs representing 21 families, 38 species of native woody plants in the Eucalyptus plantation and 36 species under Cupressus plantation were recorded. 20 species of trees, 15 species of shrubs and 7 species of shrubs / or small trees were recorded. Based on values from Shannon – Wiener’s diversity index, the diversity of species was higher in Eucalyptus vegetation (1.3) than Cupressus (1.2). The evenness value for plants under Cupressus forest was similar with Eucalyptus. A two-sample t-test was used to compare the means of native wood plants under Eucalyptus and Cupressus plantations, to determine if they are significantly different from each other. Since the p-value is less than the typical significance level, the result indicated that the type of plantation exerts an influence on the presence or abundance of native plants. The vegetation structure of native woody plants in both plantations showed that the seedling and sapling classes were relatively dominant. In general, under Eucalyptus plantations 24 species of and under Cupressus plantations 25 species of native woody plants were regenerated naturally. Exotic trees hinder native plant regrowth by outcompeting them for resources, producing chemicals that inhibit growth, altering soil and microclimate conditions, displacing native vegetation, disrupting mutualistic relationships. The study therefore suggests that introducing diverse native trees, optimizing light, managing plantation density, promoting natural regeneration, and fostering stakeholder collaboration to enhance biodiversity and ecosystem resilience in plantations, supporting native plants and broader conservation aims.