Effect of forest fragmentation and disturbance on diversity and structure of woody species in dry Afromontane forests of northern Ethiopia

Anthropogenic disturbance and fragmentation have changed the structure and composition of northern Ethiopian forests. This study was conducted to determine disturbance levels of patches, and examine the effect of anthropogenic disturbance and fragment size on diversity and structural attributes of woody species. A systematic sampling method was used to collect data and 61 nested plots of each 400 m² were used. The disturbance index was used to assess disturbance intensities. To examine the effects of fragment size and anthropogenic disturbances on woody species diversity and structure, regression analysis was performed. ANOVA was used to examine differences in woody species diversity and structural attributes among fragments. Similarities among patches were assessed by Sorensen’s similarity index. A total of 80 woody species, representing 68 genera and 43 families were recorded. Diversity, evenness, stem density ha⁻¹, and basal area were 2.8 ± 0.47, 0.73 ± 1.10, 1171.21 ± 220.10, and 39.89 ± 17.47 m² ha⁻¹ respectively. The mean number of species, evenness, and diversity were significantly different among fragments. Diversity, evenness, the mean number of species, and stem density per hectare significantly increased with increasing fragment size. Disturbance intensities varied among fragments. However, the mean basal area, mean seedling, and sapling density per hectare were not significantly affected by patch size and disturbance intensities. Generally, forest fragmentation and anthropogenic disturbance resulted in the reduction of diversity, affect woody species structure, and increased the level of disturbance. Therefore, recognizing the role of small fragments for forest conservation, minimizing further disturbance, and undertaking restoration activities in disturbed patches are strongly needed.