Woody Species Encroachment And Related Ecological Conditions In The Grass Plain Of Nechsar National Park

Encroachment of woody species has been reported as the major threats to the Grassland ofrnNechsar National Park of Ethiopia. The objectives of the study were to determine therninvasive bush species, woody species density and woody species cover; to determine plantrndiversity and community; to asses the relationships between woody species cover,rnherbaceous cover, grass cover, forbs cover, and bare land cover in the Grass plain of thernPark. Vegetation survey methodology was employed. Floristic composition, species relativernfrequency and abundancy, plant community, species diversity, species richness, speciesrnevenneness, density and cover of woody species, grass cover, forbs cover, total herbaceousrncover were determined in 75 relev`es. One hundred and thirty one plant species belongingrnto 45 different families were recorded. Dicrostachys cinerea, Acacia nilotica, Acaciarnmellifera, and Acacia Oerfota were the major woody species encroacher in the area.rnAbutilon anglosomaliae (RF = 0.95), Bothrichloa inssculpata (RF = 0.81), Rhynchosiarnmalacophylla (RF = 0.79), Endostemon tereticaulis (RF = 0.72), Commelina diffusa (RF =rn0.70), Digitaria abyssinica (RF = 0.67) were the most frequent species in the area.rnAbutilon anglosomaliae (6.5%), Dicrostachys cinerea (6%), Chrysopogon plumulosusrn(5.3%), Bothrichloa inssculpata (4.5%), Pupalia lappacea (4%), Loudetia flavida (4%) arernspecies with higher cover abundance in the Grass plain of Nechsar National Park. Thernhierarchical agglomerate cluster analysis using average linkage strategy provides sixrnmajor plant communities and one solitary releve. The low average specie richness (23spp.rnPlot-1) resulted in low over all average species diversity (2.92). ANOVA showed there is nornvariability among plant communities with respect to species diversity, richness, andrnevenneness at p≤0.05. Results also showed that woody species density was 1995 woodyrnplants ha-1. Mean cover of woody, grass, unpalatable forbs, and total herbaceous speciesrnwas 31%, 58%, 68% and 121% respectively. The bare land cover was 12%. The highrnwoody and unpalatable forbs cover indicated the progressively increasing grass speciesrndiversity deterioration in the grass plain of the Park. Relatively high bare land coverrnobserved resulted in high incidence of gully erosion in the area. Analysis of variancernshowed significant variability among the plant community at P≤0.05 for woody, grasses,rnforbs, and bare land cover. Pearson correlation coefficient matrix indicated that woodyrnspecies cover was negatively correlated with total herbaceous cover (grass and forbs) andrnbare land cover. Grass cover was negatively correlated with forbs, bare land cover, andrnwoody species density. Total herbaceous cover was negatively correlated with bare landrncover, bush density. The relationship between bush cover, woody species density, grassrncover, herbaceous cover, bare land cover and related soil erosion is complex and relatedrnto climate, land escape geology and anthropogenic disturbances. Main threats to therngrassland ecology of Nechsar National Park are progressive increase in bush cover, loss ofrngrass cover, and increase in unpalatable forbs. Currently greater than 50% of thernlandscape of the grass plain is in a poor to fair grassland conditions. Decline in therngrassland condition, unless reversed, will jeopardize the biological diversity as well asrnaesthetic value of the Nechsar National Park.

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