# The Carbon Sequestration Potential of Degraded Agricultural Land in the Amhara Region of Ethiopia
## 4 Discussion
Although differences among agro-ecological zones (Tables 3 and 4) may be more pronounced than differences between the three land use types, interesting differences in soil and above ground soil carbon sequestration among the three land use types could be revealed. Under comparable climate conditions, reforestation on bare land exhibits lower productivity rates (NPP and aboveground carbon storage) (Tables 2 and 3) versus the other land use types. We can expect that these sites have experienced the highest degradation effects, as expressed by the lowest initial soil carbon andespecially nitrogen stocks (compare Table 1). However, reforested areas on bare land showed the highest relative or net carbon and nitrogen gain (Figure 3) versus reforested grass land and shrub land (see Tables 3 and 4). This suggests that the reforestation of bare land is not just important for avoiding further soil erosion but it is also the land use type where the highest net soil carbon gain can be expected. The highest net carbon gain of the aboveground biomass can be expected for reforested areas on shrub land and grass land, versus bare land (Tables 3 and 4). These areas are often highly populated and replanting activities in these areas would address the high demand for fuel wood and timber. Some existing small-scale plantations could already show that this is possible, providing more timer and fuel wood for the local population and reduced pressure on the remaining forests [34]. In our study, we identified 1.2 Mha of grassland suitable for reforestation; however a potential land use conflict should not be ignored. Grass land is mainly used as a feed source for livestock. A study by [PERSON] et al. [81] in the highlands of Ethiopia showed that more than half of interviewed farmers (58%) grazed their animals on communal grass land. Livestock numbers and thus the demand for grazing land increases with an increasing population [81] while grassland is increasingly converted to crop land, either illegally or legally by government initiatives to feed the fast growing Ethiopian population (2.5% increase per year) [82]. Any successful reforestation project must be simple and should include a forest management plan that integrates harvesting options. Forest management strategies that address both the local people's wood demand and a maximum carbon sequestration potential are an effective incentive for large-scale reforestation programs [83]. Therefore, we analyzed three thinning scenarios (unthinned, thinning 1-5% every 20 years, and thinning 2-10% every 20 years) and a Normal-forest system with different rotation lengths. In all applied thinning scenarios, the aboveground and soil carbon stock increased compared to the initial stock (Figure 3), indicating a gain in soil fertility (Figure 3). Thinning allows the harvest of a certain portion of biomass [18]. Lowered stand density reduces competition, improves the light conditions, and activates decomposition processes, which leads to higher individual growth rates. Note that the thinning impact on the soil conditions by scenario is negligible (Tables 3-6). An important conceptual goal of our study was to provide a long term implementation path for establishing sustainable forest management, including options for a sustainable production and continuous wood supply [84] for the farmers in the region. Practical considerations at the beginning of a large reforestation program need to involve the limitations in the production of planting material, education, and limitation in the work force [85]. Furhtermore the weather conditions at the time of and preceding the planting activity planting are important (i.e., to avoid local droughts and only plant when soils are well saturated). In our study we suggested to expand the planting activities over several years. This helps to organize the logistics but also establishing the proposed 'Normal-forest' system. This approach will also provide a patchy forest landscape of different development stages, which favors biodiversity [86].