Effects of Land Cover Changes on Soil Organic Carbon and Total Nitrogen Stocks in the Eastern Mau Forest Reserve, Kenya

This study analysed the variations of soil organic carbon (SOC) and total nitrogen (TN) stocks under natural forests (NF), plantation forests (PF), bamboo forests (BF), and croplands that had been converted from such forests (i.e., NF2C, PF2C, and BF2C) in the Eastern Mau Forest Reserve using field, laboratory, spatial, and statistical techniques. The results displayed significant differences in SOC and TN stocks between NF and NF2C (p < 0.0001), and between PF and PF2C (p < 0.0001). For instance, the surface soils (0–15 cm) of NF had the highest SOC and TN stocks (71.6 and 7.1 Mg ha−1, respectively), while NF2C had the lowest (35.4 and 3.5 Mg ha−1). Similarly, the subsurface soils (15–30 cm) of NF had the highest stocks (55.7 and 5.6 Mg ha−1), while NF2C had the lowest (32.5 and 3.2 Mg ha−1). This reflects a decline in both SOC and TN stocks by about 51 % in the surface and about 42 % in the subsurface soils after NF conversion. There were also significant differences in SOC and TN stocks (p < 0.05) between the surface and subsurface soils of different land cover types. The stocks decreased as soil depth increased. This trend suggests that (i) forest-to-cropland conversions are undermining the ecosystem’s capacity for carbon sequestration, and (ii) subsurface soils have potential for carbon sequestration. SOC and TN losses in the croplands may be mitigated by adopting best management practices (BMPs), especially agro-forestry. These findings are useful for designing sustainable land management (SLM) and carbon sequestration projects.