Ecological and floristic study of Hirmi woodland vegetation in Tigray Region, Northern Ethiopia

Abstract

The dryland area in Ethiopia covers a substantial region endowed with diverse plant resources. However, the landmass has received less attention even if it has high ecological, environmental, and economic uses. The present study was conducted in Hirmi woodland vegetation, which is one of the dryland areas in Ethiopia, with the objective of investigating the floristic composition, plant community types, vegetation structure, community-environment relations and its regeneration status. Vegetation and environmental data were collected from 80 sampling plots with a size of 25 m × 25 m designated as the main plots. Diameter at breast height (DBH), height, basal area, density, vertical structure, importance value index (IVI), and frequency were computed. Species diversity and evenness were analyzed using Shannon diversity and evenness indices. The plant community types and vegetation-environment relationships were analyzed using classification and ordination tools, respectively. A total of 171 vascular plant species belonging to 135 genera and 56 families were recorded. About 5.3% of the species were endemic and near-endemic to Ethiopia. The highest number of species was recorded in families Fabaceae (16.4%) and Poaceae (11.7%) followed by Asteraceae (7.0%), Combretaceae, Lamiaceae, and Moraceae (3.5% each). Five plant communities were identified. According to the results from ordination analysis, the floristic composition of these plant communities was significantly affected by altitude, slope, sand, silt, soil organic matter, total nitrogen, and disturbance. The vegetation structure reveals that a large number of individual species was categorized in the lower DBH, frequency, and height classes. The highest Shannon diversity index and evenness values of the study area were 4.21 and 0.95, respectively. Anogeissus leiocarpa, Combretum hartmannianum, Ziziphus mucronata, Terminalia macroptera, and Acacia polyacantha were the species with high IVI. Some endemic plants were in the IUCN red list categories of Ethiopia and Eritrea. The overall regeneration status of the study area was poor because of anthropogenic disturbances and grazing pressures. Although the study area is endowed with high plant species diversity including endemism, it is under poor regeneration status due to various disturbances. To overcome this challenge, integrated management measures including monitoring and application of restoration techniques by taking into consideration the significant environmental factors associated with species diversity as well as observed regeneration status and IUCN threat level of the species are highly recommended.