Carbon sequestration and vegetation properties across the age of community managed exclosures in Northern Ethiopia

Abstract

Exclosure management is becoming a common approach to rehabilitate and increase net biomass productivity of extremely degraded areas in Northern Ethiopia. However, the effect of age of exclosures on vegetation and soil property of communal lands is not yet well studied. In this study, the effect of land exclusion and age of exclosure on plant species richness, diversity, density and dominance, herbaceous standing biomass, woody biomass, woody biomass carbon, soil organic carbon (SOC) and other soil properties were assessed. To study the above listed variables, exclosures in three age classes (5–7, 12–15 and >20 years) and adjacent free grazing areas were selected. We replicate each age class three times considering agroecological similarity. From each exclosure and free grazing area, six larger plots (10m × 20m) each having five small quadrats were taken. Totally, 72 larger plots and 360 small quadrats were sampled. The result of this study indicates that exclusion of communal lands significantly improved species richness, diversity, biomass, woody biomass carbon, SOC, total nitrogen (TN) and total potassium (TK). Similarly, the density of perennial species and the density of grass species were found increased with the age of exclosure. Herbaceous species richness, diversity and annual species density were higher in the young-aged exclosures than in the older exclosures. Woody species richness, diversity, density, biomass, and woody biomass carbon were highest in the older exclosures. Besides, age of exclosure increases the content of SOC, TN and TK. Furthermore, it was found that the old-aged exclosures stored more biomass carbon (267 %) and SOC (37.66 %) than the young-aged exclosures. The study indicates the benefits of land exclosure for permanent carbon storage, which is vital to reduce atmospheric greenhouse gas concentration.