The Main Ecological Components of the Management of Dryland Natural Forests

Abstract

This study was conducted at Al Halba and Wad Gabur area, west of Ed Dueim-White Nile State. The area is known to be rich in its natural forests which are facing continuous deterioration practices due to the absence of management plans. The study is designed to investigate and understand the dynamics of the main ecological components of natural forest system and its related and integrated components affecting their sustainable management. The components include the topography and its related vegetation types (trees, shrubs and grasses). Um Sunta forest was selected as a model or example of natural forests that cover the drylands of Western Ed Dueim and spread naturally as a formation according to the soil, topography and climate of the region. This model could provide inference of the same conceptual frame for other natural forests in the area. The study investigates the dynamics of the vegetation structure and composition as affected by variations in the soil, topography and climate. The study revealed that three main sites were identified in the forest formations that replicate themselves randomly and termed as zones for the purpose of this study: Zone I; An area sloping from hillsides, extending along an open grazing area almost without trees or shrubs and covered by herbaceous vegetation, mainly dominated by Gaw, Abu assabi and Sharaya. Zone II; Moderate slope areas that lie between zone I, and III as a transitional zone. Trees and shrubs are scattered along the area with a ground cover of herbaceous plants. The dominant tree species are Samur and Sayal, while the dominant herbaceous species are Haskaneet, Gaw and Abu assabi. Zone III; Wetlands that extend along depressions (khors and wadies), covered by dense trees compared with other zones and different grass types that are adapted to the site characteristics. The dominant tree species are Sayal and Talih, while the dominant herbaceous species are Difra, Khodra and Rabaa. The variation in the site components created a complicated system that needs investigation and understanding prior to any management practices. The study investigated three main parameters in each of the three identified sites for two successive seasons (2001-2002). Investigations included ground cover assessment, tree cover assessment and soil seed bank. According to the condition of the forest from the data collected and the forest history, a cover percentage of less than 50, 30 and 10 and a bare soil percentage of more than 40, 60, and 80 may be critical for the perpetuity of forest resources of the three sites I,II and III respectively. A litter percentage of less than 10 for all sites is a causative factor for erosion hazards. Gaw, Sharaya and Abu assabi were dominating zone I and II, but they invade zone II when rainfall decline from the annual average. Haskaneet dominated zone II only on good rainfall seasons. Rabaa, Khodra and Difra dominated zone III, only when rainfall amount and distribution is suitable for their growth. The occurrence of different species in different zones depends on their adaptability to the site characteristics and their growth requirements. Tree density across the three zones varies according to topography, soil moisture and other factors. A density of less than 5 and 66 stem/ha for zone II and III respectively, may be critical for site stability and erosion hazard. Herbage mass production varies between different zones according to tree density and other local factors such as soil moisture and topography. Biomass production of less than 0.5, 0.05, and 0.01 ton/ha may be critical for stability of zone I, II, and III respectively. The study revealed that tree layering is a good indicator for studying stand development and growth. The disappearance of species from the lower layers indicates the potential decrease of their utilization and the future of their re-growth. The study revealed that there is a variation between seed bank and the above ground vegetation, which may indicate the importance of studying the seed dormancy and dispersion, and hence complete the picture about the vegetation dynamics. The study concludes that management components should be carefully studied and understood, and it made a design showing the existing status and the anticipated values. The design indicators can be used for integrated management of these natural forests.