Carbon Stock Under Four Different Land-Use Systems In The Savanna Ecosystems, In Ghana

The savanna ecosystem is currently undergoing rapid and wide-ranging changes in land use and vegetation due to degradation and deforestation. Rates of land-use change which causes changes in carbon stock following degradation and deforestation are the determined factors of carbon emissions in tropical savanna ecosystem in Ghana. The study was conducted to assess the impact of four different land-use systems namely; natural forest, teak plantation, cultivated land and fallow land on carbon stock and to determine carbon emission factors in the four land uses. This was carried out in Walewale which is guinea savanna ecosystem in Ghana. Carbon accumulation in trees, herbaceous plants, litter and soil (up to 40cm depth) were assessed. Temporary Sampling Plots (TSPs) of size 25m by 25m, giving rise to an area of 0.0625ha were created in the various land-use systems in the selected sites in forest districts. The TSPs were created to capture the variability of the particular stand characteristics. All trees in the various land-use systems that were above two meters were inventoried and stem diameter at breast height of 1.3m measured, a standard point of measuring tree diameter. In addition, four sub-plots (quadrats) of size 1.0m by 1.0m were created in all the TSPs. All herbaceous and woody plants in the sub-plots were destructively sampled and litter collected. Fresh weights were determined immediately using electronic (digital) mass measure, and samples of the plant and litter collected for dry weight determination, by oven drying to constant weight. Sub-samples were also reserved for carbon content analysis. Soil samples were collected from the soil depth of 0 to 20 cm and 20 to 40 cm within the quadrates, air dried and sieved through 2.0 mm mesh, and texture and soil organic C content determined. Soil organic C was determined in the laboratory by Walkley and Black (1934) method. The mean carbon content of litter, herbs and wood was in increasing order of 30.2% ±3.906 (SD), 35.01%±4.095 (SD) and 45.43%±2.110 (SD) respectively. There was significant difference in carbon content among the various plant functional type (P<0.05). The highest total carbon stock was recorded in the natural forest with 62.592 Mg C ha-1 followed by teak with 52.3205 Mg C ha-1 and cultivated land recorded the least total carbon of 34.564 Mg C ha-1. In terms of tree carbon stock, the highest was recorded by teak stand with 26.644 Mg C ha-1 followed closely with natural forest which recorded 26.052 Mg C ha-1. The highest total soil carbon stock was recorded in the natural forest with 36.35 Mg C ha-1 followed by fallow land which recorded 34.02 Mg C ha-1. However, for the top 0-20cm, the highest carbon stock was in the fallow land followed by natural forest and cultivated land whiles the teak stand had the least. At P<0.05, there was significant difference in the total soil carbon among the various land-use systems. Post Hoc LSD test shows that the mean difference between natural forest versus fallow land, and fallow land versus cultivated land was not statistically significant. However the mean difference between natural forest versus cultivated land, natural forest versus teak plantation, fallow land versus teak plantation, and cultivated land versus teak plantation was found to be statistically significant. Using the natural forest as a bench mark, the impact of carbon loss on the conversion of the natural forest to other land-use systems was found was in increasing order, teak plantation, fallow land and cultivated land. Using teak plantation as a bench mark, more carbon is gained in converting cultivated land to teak plantation than in converting fallow land to teak plantation.

Source: KNUST