Soil organic carbon stocks and related soil properties in a primary Picea abies (L.) Karst. volcanic-mountain forest

Although many published studies have evaluated soil organic carbon (SOC) stocks in forest soils, none have yet focused on primary (i.e., unlogged) spruce (Picea spp.) forests on volcanic rocks. Previous research in the Calimani volcanic mountain range, Romania, revealed a close relationship between soil morphology and the canopy disturbance history of a primary spruce (Picea abies L. Karst.) forest in the area. Here, six representative soil profiles were chosen from a large pedological study to test the hypothesis that the different disturbance regimes of the study plots had significant effects on SOC stocks. We used a combination of traditional soil core and excavation methods, modified for soil sampling and SOC stock estimations by horizons. In addition, chemical soil properties such as pH and the contents of Al, Fe, and Si in selected extracts (oxalate-extracted Al-o, Fe-o, and Si-o, pyrophosphate-extracted Al-p and Fe-p) were determined to detect diagnostic properties of the soils. Total SOC stocks in the organic horizons plus mineral soil to the 0.5 m depth ranged from 18.2 to 32.0 kg C m(-2). In the 0-0.5 m depth, the SOC stocks were significantly positively correlated with the severity of the maximum-recorded canopy disturbance. The SOC contents in mineral soil down to the 1.0 m depth were positively correlated with the contents of Al-p + Fe-p, especially in the subsoil horizons. A strong positive correlation was found between pH(KCl), Si-o contents, Al-p - Al-o contents, and the Al-o/Fe-o ratio. The soils were classified as Podzols and Andosols. Our results indicate that in primary spruce-dominated forests on volcanic rocks, the regime of high-severity natural canopy disturbances may have positive effects on SOC accumulation in the mineral soil. The Al-o/Fe-o ratio may be a potentially useful proxy for the relative degree of leaching and podzolization in these soils.