Tree population structure, diversity, regeneration status, and potential disturbances in Abu Gadaf natural reserved forest, Sudan

Abstract

Forests and forest trees have continuously been supporting human beings through the provision of food and food-associated materials, fodder and foraging sites for their livestock, and medicinal materials, as well as multiple ecological services. However, unbalanced utilization of these resources and the biotic and abiotic disturbances interrupt their sustainability and ecological functions. We studied the tree population structure, diversity, and regeneration status of tree species in the Abu Gadaf Natural Reserved Forest in 46 sample plots of 20 m x 50 m (1000 m2) distributed systematically throughout the reserve over a year. The study findings showed that highland sites have higher tree species richness (47 species) compared to lowland sites (31 species) and the highest contributors are Combretaceae (21.3%) and Fabaceae (19.2%) families. Moreover, seedlings in highland sites are twice that of lowlands, with a significant difference between the two sites (F1,46 = 138.4, p < 0.001). The same trend has been observed for saplings and adult trees (F1,46 = 143.2, p < 0.01; F1,46 = 126.7, p < 0.01, respectively). Likewise, all dendrometric parameters and diversity indices demonstrated significant differences between the sites across the reserve with lower values in the lowland sites and vigorous regeneration in the highland sites (T = 33.7, P < 0.001; T = 22.3, P = 0.001; T = 27.9, P = 0.042, respectively). The study concludes that over browsing by livestock and intensive illegal tree logging in the lowland sites have severely affected the tree population composition, which might consequently disturb the regeneration process and seedlings recruitment. A conservation action plan is urgently needed to protect vulnerable species, especially those with low importance value index.