Plant Diversity and Relationship between Plant Communities and Environmental Variables in Combretum-Terminalia Woodland, Western Ethiopia

Abstract

The aim of the study was to determine plant community types and species distribution patterns and their relationships with environmental variables in Dabena woodland in western Ethiopia. A systematic sampling design was used. Representative and relatively homogeneous vegetation units of sampling sites were selected on the basis of physiognomy. Vegetation and environmental data were collected from a total of 92 plots (each 20 m × 20 m) which were placed at intervals of 200 m along the established transect lines. All vascular plant species in the plots were recorded. Floristic richness, diversity, evenness indices, and similarity of the plant communities were analyzed using R Package 3.2. Classification and ordination methods were used to describe community types and to examine the relationship between community type and environmental variables. Five plant communities were identified in the vegetation of Dabena woodland, namely, Clerodendrum myricoides-Vernonia hymenolepis, Erythrina brucei-Entada abyssinica, Combretum molle-Gardenia ternifolia, Galiniera saxifraga-Flacourtia indica, and Dracaena afromontana-Landolphia buchananii. All community types showed a high diversity index. The highest similarity coefficient was 0.49 between community types two and three, reflecting 0.51 dissimilarity in their species richness. Disturbance, altitude, CEC, phosphorous, OC, clay, and TN are the environmental factors that most influenced the distribution of the plant communities. The CCA diagram revealed that disturbance and silt strongly influenced the distribution of species in Clerodendrum myricoides-Vernonia hymenolepis community, Combretum molle-Gardenia ternifolia community, and Erythrina brucei-Entada abyssinica community. Altitude, clay, and total nitrogen axes strongly influenced the distribution of species in Galiniera saxifraga-Flacourtia indica and Dracaena afromontana-Landolphia buchananii community. Therefore, it can be concluded that some other environmental variables may influence the distribution of the plant communities, which needs to be further investigated.