Assessment of woody species encroachment in the grasslands of Nechisar National Park, Ethiopia

Ecological survey was executed to assess woody species encroachment into the grassland plain of Nechisar National Park (NNP). Forty-one woody species were recorded. Dichrostachys cinerea Wight & Arn., Acacia mellifera (Vahl) Benth., Acacia nilotica (L) Willd., Acacia senegal (L.) Willd., Acacia seyal Del. and Acacia tortilis (Forssk.) Hayne were among the major encroaching woody species. The majority of the woody species were found to be highly aggregated in their pattern of distribution, while only few species showed some degree of randomness. The mean woody species density was ca. 1995 woody plants ha-1. Mean cover of woody, grass, unpalatable forbs and total herbaceous species were 31%, 58%, 68% and 121%, respectively. The woody species density and cover, unpalatable forbs and bare land cover were significantly higher in the highly grazed and fire-suppressed part of the grassland plain. Pearson correlation coefficient matrix indicated that woody species cover and density were negatively correlated with total herbaceous and grass cover. The high woody, unpalatable forbs and bare land cover indicated the progressively increasing perennial grass species diversity deterioration in the grass plain of the Park. Decline in the grassland condition, unless reversed, will jeopardize the biological diversity as well as the aesthetic value of the NNP.