Changes in woody species composition following establishing exclosures on grazing lands in the lowlands of Northern Ethiopia

Abstract

Restoring vegetation in low rainfall areas is difficult and urges the need to design an effective and low-cost method of vegetation restoration. This study was undertaken in the lowlands of northern Ethiopia to: (1) investigate how exclosure age affects restoration of degraded native plant species richness, diversity and aboveground standing biomass, and (2) identify soil characteristics, which affect effectiveness of exclosures to restore degraded native vegetation. Replicated (n = 3) 5-, 10- and 15- year-old exclosures were selected and each exclosure was paired with an adjacent grazing land to detect changes in vegetation variables following establishing exclosures on communal grazing lands. All exclosures displayed higher species richness, diversity and aboveground biomass when compared to the adjacent grazing lands. Results on vegetation composition indicate that all exclosures are at early stage of succession. In all exclosures and grazing lands, vegetation variables displayed significant (p < 0.05) correlations with soil variables indicating that consideration of soil fertility will help enhance natural regeneration in exclosures. Our study indicates that the establishment of exclosures on degraded communal grazing lands can be effective in restoring degraded native vegetations, and with time, exclosures may obtain an important role as source of seeds of indigenous woody species.
Key words: Grazing pressure, land degradation, land use conversion, native vegetation, soil variables, vegetation restoration.