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

摘要: Ecological survey was executed to assess woody species encroachment into the grassland plain of Nechisar National Park (NNP). Forty-one were recorded. Dichrostachys cinerea Wight & Arn., Acacia mellifera (Vahl) Benth., nilotica (L) Willd., senegal (L.) seyal Del. and tortilis (Forssk.) Hayne among major encroaching species. The majority found be highly aggregated in their pattern distribution, while only few showed some degree randomness. mean density ca. 1995 plants ha−1. Mean cover woody, grass, unpalatable forbs total herbaceous 31%, 58%, 68% 121%, respectively. cover, bare land significantly higher grazed fire-suppressed part plain. Pearson correlation coefficient matrix indicated that negatively correlated with grass cover. high progressively increasing perennial diversity deterioration Park. Decline condition, unless reversed, will jeopardize biological as well aesthetic value NNP. Resume Une etude ecologique fut faite pour evaluer l’envahissement des especes ligneuses dans la plaine herbacee du NNP. Quarante et une furent enregistrees. comptaient parmi les plus envahissantes. On a trouve que majorite avaient un schema de distribution fortement groupe tandis seule quelques etait, certain degre, aleatoire. La densite moyenne etait d’environ plants par hectare. couverture ligneuses, graminees, herbes dicotyledones non comestibles, herbeuses leur ensemble 121% respectivement. comestibles surface sol nu etaient significativement elevees parties pâturees protegees feux herbeuse. Une matrice indique negativement liees totale celle graminees. forte le indiquent en rapide diversite graminees herbeuse parc. Le declin l’etat prairie, s’il n’est pas inverse, va mettre danger biologique, mais aussi valeur esthetique NPP.