Woody Species Encroachment and Related Ecological Conditions in the Grass Plain of Nechsar National Park

No Thumbnail Available



Journal Title

Journal ISSN

Volume Title


Addis Ababa University


Encroachment of woody species has been reported as the major threats to the Grassland of Nechsar National Park of Ethiopia. The objectives of the study were to determine the invasive bush species, woody species density and woody species cover; to determine plant diversity and community; to asses the relationships between woody species cover, herbaceous cover, grass cover, forbs cover, and bare land cover in the Grass plain of the Park. Vegetation survey methodology was employed. Floristic composition, species relative frequency and abundancy, plant community, species diversity, species richness, species evenneness, density and cover of woody species, grass cover, forbs cover, total herbaceous cover were determined in 75 relev`es. One hundred and thirty one plant species belonging to 45 different families were recorded. Dicrostachys cinerea, Acacia nilotica, Acacia mellifera, and Acacia Oerfota were the major woody species encroacher in the area. Abutilon anglosomaliae (RF = 0.95), Bothrichloa inssculpata (RF = 0.81), Rhynchosia malacophylla (RF = 0.79), Endostemon tereticaulis (RF = 0.72), Commelina diffusa (RF = 0.70), Digitaria abyssinica (RF = 0.67) were the most frequent species in the area. Abutilon anglosomaliae (6.5%), Dicrostachys cinerea (6%), Chrysopogon plumulosus (5.3%), Bothrichloa inssculpata (4.5%), Pupalia lappacea (4%), Loudetia flavida (4%) are species with higher cover abundance in the Grass plain of Nechsar National Park. The hierarchical agglomerate cluster analysis using average linkage strategy provides six major plant communities and one solitary releve. The low average specie richness (23spp. Plot-1) resulted in low over all average species diversity (2.92). ANOVA showed there is no variability among plant communities with respect to species diversity, richness, and evenneness at p≤0.05. Results also showed that woody species density was 1995 woody plants ha-1. Mean cover of woody, grass, unpalatable forbs, and total herbaceous species was 31%, 58%, 68% and 121% respectively. The bare land cover was 12%. The high woody and unpalatable forbs cover indicated the progressively increasing grass species diversity deterioration in the grass plain of the Park. Relatively high bare land cover observed resulted in high incidence of gully erosion in the area. Analysis of variance showed significant variability among the plant community at P≤0.05 for woody, grasses, forbs, and bare land cover. Pearson correlation coefficient matrix indicated that woody species cover was negatively correlated with total herbaceous cover (grass and forbs) and bare land cover. Grass cover was negatively correlated with forbs, bare land cover, and woody species density. Total herbaceous cover was negatively correlated with bare land cover, bush density. The relationship between bush cover, woody species density, grass cover, herbaceous cover, bare land cover and related soil erosion is complex and related to climate, land escape geology and anthropogenic disturbances. Main threats to the grassland ecology of Nechsar National Park are progressive increase in bush cover, loss of grass cover, and increase in unpalatable forbs. Currently greater than 50% of the landscape of the grass plain is in a poor to fair grassland conditions. Decline in the grassland condition, unless reversed, will jeopardize the biological diversity as well as aesthetic value of the Nechsar National Park.