An investigation on the effect of altitude on soil organic carbon storage and some other soil properties in Arasbaran forests

Investigation of soil attributes is one of the ways to evaluate and manage forest ecosystems. Altitude is considered as one of the effective factors on the soil quality, especially soil organic carbon (OC). However, variation of the soil OC stocks at different altitudes of Arasbaran forests is still unknown. Therefore, this study was conducted to examine the spatial distribution of OC values, and some other chemical properties in different soil depths affected by altitude in Arasbaran forests.

In this study, a factorial experiment was conducted in a randomized complete block design in three replications. Overall, 60 soil samples were collected on a north slope of the region at four different altitude ranges, including 0–600, 600–1200, 1200–1800, and 1800–2400 m, and from five soil depths of 0–20, 20–40, 40–60, 60–80, and 80–100 cm. Then, the amounts of OC, cation exchange capacity (CEC), dilute-acid-soluble and hot-water-soluble carbohydrates, calcium carbonate, available phosphorus and potassium as well as soil acidity (pH) were determined in the soil samples.

The results showed the significant effect of soil depth, altitude and their interaction on most of the studeid soil properties. In fact, with increasing elevation and soil depth, the amount of OC, CEC, and dilute-acid-soluble carbohydrates increased and decreased, respectively, and a very strong correlation was found between them. Additionally, on average more than 50% of the OC was allocated to the top 20 cm of the soils at all four elevations that reduced averagely about 79% with increasing soil depth to the depth of 80–100 cm. Moreover, the highest increase rate of OC contents with altitude of about 9% was observed between the elevation ranges of 600–1200 and 1200–1800 m. Furthermore, with increasing altitude and soil depth, other soil properties such as pH, calcium carbonate, and available potaium showed a decraese of about 2%, 16%, and 16%, and an increase of around 4%, 16%, and 18%, respectively. In addition, with increasing soil depth, the amount of soil available phosphorus increased; meanwhile, the effect of altitude on this parameter was not significant.

Based on the findings of this study, soil OC stocks and overall the quality of Arasbaran forest soils are significantly affected by the factors of altitude and soil depth so that surface soils of higher elevations in the study area are of higher quality in terms of OC content, CEC, and dilute-acid-soluble carbohydrates, which should be given more attention. In fact, considering the significant role of these soils in carbon sequestration, these areas should be preserved intact and undisturbed through proper management as well as various protection practices.