Above ground carbon stock assessment and economic analysis of Eucalyptus globulus plantations and exclosures in the highlands of Tigray, Ethiopia

Abstract

In Tigray, northern most part of Ethiopia, deforestation and subsequent land degradation is the major environmental and economical problem. In attempt to reverse this, exclosures and eucalyptus tree plantations was established on degraded lands. However no studies have been made to assess above ground carbon stock in these land uses or to quantify carbon benefits provided by theses land uses. This study aimed to assess above ground carbon stock in exclosures, E.globulus plantations and open grazing lands and evaluate the cost and benefit of adopting the two forest management systems including carbon benefit. The assessment of above ground carbon stock was based on biomass of trees/shrubs, herbs and litters. Above ground biomass was estimated using both destructive and non destructive methods and above ground carbon stock was calculated using 50% conversion factor from biomass to carbon. The results of above ground carbon pool showed significant variation (P < 0.001) between the different land uses. The mean total above ground carbon stock was 29.5 ± 16.7 Mg/ha, 2.75 ± 0.96 Mg/ha and 0.54 ± 0.13Mg/ha in the E.globulus plantations, exclosures and open lands respectively. Carbon density was higher in the woody biomass than in herbaceous and litter biomass, in all land use types. Carbon density in woody and litter biomass was largest in the E.globulus plantations (28.79 ± 16.45 Mg/ha and 0.51 ± 0.18 Mg/ha, respectively). Carbon density in herbaceous biomass was how ever higher in the exclosures (0.53 ± 0.18 Mg/ha) than the adjacent open lands and E.globulus plantations. Managing degraded lands by closing for human and animal interference and planting eucalyptus trees, have significant positive impact of the accumulation of carbon. Ex-ante net benefits from exclosures, E.globulus plantations and crop lands were determined using the Net Present Value (NPV) criterion. Two scenarios were formulated for the economic analysis of exclosures; (1) economic analysis considering honey benefit and (2) excluding honey benefits. The average financial Net present values were 60494 ETB/ha and 3910 ETB/ha for scenarios one and two of exclosures respectively, and 34729 ETB/ha for E.globulus plantations. Based on carbon price of 10 US $ per Mg, benefit from carbon increased the total NPV by an average of only 0.5% and 1% in the exclosures and E.globulus plantations respectively. The financial return from exclosures with honey production and E.globulus plantations were by 56609 and 30844 ETB/ha higher than the NPV from crop production (3885 ETB/ha) respectively. Sensitivity analysis showed exclosures and E.globulus plantations always provide positive financial return. Thus establishing exclosures and E.globulus plantations on degraded land provide positive financial return.