Spatiotemporal changes in woody species composition, diversity, and regeneration reveal rapid degradation of a savanna woodland in Blue Nile state, Sudan

Abstract

Forests and tree species provide vital resources and ecosystem services, but unsustainable use and disturbances have degraded their ecological integrity. This study assessed forest dynamics in the Elnour Natural Forest Reserve (ENFR) by analyzing species composition, diversity, and natural regeneration in 229 sample plots (1,000 m 2 each) during 2008 and 2021. Over a 13-year period, the Wilcoxon signed-rank test revealed significant temporal changes in several forest structural and regeneration attributes between 2008 and 2021. Tree species decreased from 35 to 19 species and the number of families from 12 to 8. The Fabaceae and Combretaceae remained dominant by contributing over 55% of the species composition. Additionally, mean tree density declined significantly ( W = 582, Z = 4.37, p < 0.0001) resulting significant decrease in basal area ( W = 310.50, Z = 3.97, p < 0.0001) during this period. Sapling density also differed significantly ( W = 328, Z = 2.38, p = 0.017) between the two inventory periods. However, no discernable variation ( W = 11, Z = 0.80, p = 0.418) was observed in seedling density between 2008 and 2021. Relative frequency analysis revealed decline in formerly dominant species, including Vachellia seyal (14.58 to 14.48%) and Senegalia senegal (7.76 to 4.83%) while an increase in disturbance-tolerant shrubs such as Vachellia oerfota var. oerfota (0.17 to 10.09%) and Senegalia mellifera (0.67 to 2.41%). Regeneration status showed marked variation with a fewer species showing good regeneration while many species exhibiting no regeneration, indicating severe recruitment bottlenecks during this 13-year period. The findings highlight an urgent need for targeted conservation measures, sustainable forest management, and assisted regeneration to restore ecological integrity and maintain biodiversity in rapidly degrading dryland forest landscapes of Sudan.