Vegetation Composition in Hugumbirda-Gratkhassu National Forest Priority Area, South Tigray

Abstract

The floristic composition and structure of the vegetation of Hugumbirda-Grat-Khassu forest, South Tigray, Northern Ethiopia is described and related to environmental factors. To analyze the vegetation and environmental data seventy-four relevè ( 20m x 20m) were used. For each species the cover/abundance value was estimated. Height and diameter at breast height (DBH) of all woody individuals taller than 2 m and thicker than 2 cm were measured. Importance Value Index was calculated for 24 tree/shrub species and the result helped to identify the five dominant tree/shrub species and to show the overall forest situation. The species and relevès were classified with the two-way indicator species analysis program TWINSPAN. We recorded 102 species belonging to 83 genera and 50 families. Five community types are described: Allophylus macrobotrys-Ficus sur, Nuxia congesta-Podocarpus falcatus, Acacia abyssinica-Olea europaea, Myrica salicifolia-Erica arborea-Maesa lanceolata and Acacia etbaica- Dichrostachys cinerea-Acacia tortilis type. Of these, community type 2 has high species richness while community type 3 is poor in species richness. The general arrangement of all species was found to show high density at lower height and DBH classes. Based on the cumulative results of Importance Value Index, Juniperus procera, Olea europaea subsp. cuspidata, Nuxia congesta, Cassipourea mallosana and Olinia rochetiana were identified to be the most dominant tree species of the forest and they contributed 71.43% of the basal area. Analysis of community-environment relationships didn’t show significant differences except for altitude and slope.

Key words: Community, DBH, Floristic composition, Forest structure, Releve, Vegetation classification.