Multivariate analysis of the effects of environmental factors on plant diversity and composition in the Afar Rangelands, Northeast Ethiopia

The structure and biodiversity of natural vegetative communities are increasingly threatened by invasive species. Prosopis juliflora (Fabaceae) is a major invasive shrub in Africa, Australia, and North America. However, how its invasion is related to plant diversity and composition, and whether this varies with aspect, altitude, slope, and anthropogenic disturbances remains poorly understood. The aims of this study were to evaluate the relationships between P. juliflora invasion, floristic diversity and composition, and altitude, slope, aspect, and anthropogenic disturbance in the Afar region of Northeastern Ethiopia. The research examined two main hypotheses: (1) P. juliflora invasion was related to the diversity of native plant species; (2) native species diversity decreased with increasing aspect, altitude, slope, anthropogenic disturbances, and grazing. Sixty-four sample quadrats were placed in woodland vegetation using stratified random sampling. Quadrats measuring 1 m2, 100 m2, and 400 m2 were used to record the abundance and percent cover of herbs, seedlings and saplings, and trees, respectively. Physiographic variables and human activities were also recorded in the 400 m2 quadrats. Plant species diversity was unaffected by aspect, slope, grazing intensity, and disturbance (p > 0.05). However, plant diversity and composition were affected by altitude, P. juliflora invasion levels, and anthropogenic factors (p < 0.05). Three plant community types were identified using canonical correspondence analysis and P. juliflora had a negative relationship with native plant diversity in the third plant community type. Revisiting plots in the future will provide evidence to support lower plant diversity as a cause or effect of P. juliflora invasion.