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.
Highlights
Terrestrial biodiversity represents the richest diversity in the tropics and near to the equator (Gaston 2000), which seems to be the result of the warm climate, high primary productivity and diverse topography in the region (Field et al 2009)
Out of the total plant species identified from the study area, 9 (5.3%) species were found endemic (7 species) and near-endemic (2 species) to Ethiopia according to the flora of Ethiopia and Eritrea and Friis et al (2010)
The Hirmi woodland is dominated by undifferentiated floristic composition that belongs to Combretum—Terminalia and Acacia—Commiphora woodland vegetation types with a small section of dry evergreen Afromontane forest (DAF) vegetation types in the elevated areas
Summary
Terrestrial biodiversity represents the richest diversity in the tropics and near to the equator (Gaston 2000), which seems to be the result of the warm climate, high primary productivity and diverse topography in the region (Field et al 2009). About 40% of the global tropical forest area (Mayaux et al 2005) and 14% of the total African land surface (Eshete et al 2011) is covered by the dry woodland vegetation. Deforestation and habitat degradation in the dryland area resulted several socioeconomic and environmental challenges that bring a strong impact on the capacity of the forests to provide rich ecosystem services (Nyssen et al 2007). To mitigate these challenges, conservation of biodiversity in the dryland ecosystems has been receiving greater international attention from time to time (CBD 2006; Lemenih and Bongers 2011). Effective conservation activities in dryland forests definitely demand an exhaustive investigation on environmental determinants such as soil properties, elevation, habitat suitability, habitat diversity, and species interaction (Arponen 2012; Yismaw et al 2014)
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