Impact of topographic aspect and vegetation (native and reforested areas) on soil organic carbon and nitrogen budgets in Mediterranean natural areas.

Soil organic carbon (SOC) plays a critical role in the global carbon (C) cycle, and C sequestration in forest soils can represent a C sink. A relevant question is how does SOC changes in space and time; consequently, the study of the influence of topographic aspect on SOC stocks (SOCS) is very important to build a complete understanding of the soil system. In this line, four topographic aspects, north (N), south (S), east (E) and west (W) were studied under two different plant communities; native forests (NF) and reforested areas (RF) in the Despeñaperros Natural Park (S Spain). Five soil profiles were sampled at each of six different sites, 2 sites for NF (N and E) and 4 sites for RF (N, S, E and W). Soil properties were studied at different depths using soil control sections (S1: 0-25 cm; S2: 25-50 cm; S3: 50-75 cm). The results indicate that RF (N: 147.1 Mg ha(-1); E: 137.3 Mg ha(-1); W: 124.9 Mg ha(-1) and S: 87.0 Mg ha(-1)) had increased total SOCS compared to NF (N: 110.4 Mg ha(-1) and E: 80.9 Mg ha(-1)), and that SOCS in the N position were higher than in the other topographic aspects. Therefore, the results suggest that topographic aspect should be included in SOCS models and estimations at local and regional scales.