Estimating organic carbon stock at soil profile scale of forest soils in an area of southern Italy

Soil organic carbon (SOC) stored and cycled under forests is one of the largest carbon reservoirs that is in rapid exchange with atmospheric CO2, and it is thus important as a potential source and sink of the greenhouse gas over time scales of human concern. Estimates of soil organic carbon (SOC) stocks are required to quantify carbon sources and sinks to understand how ecosystems would respond to natural and anthropogenic disturbances under different management strategies. The present study was carried out within the project LIFE09 ENV/IT/078 "Managing forests for multiple purposes: carbon, biodiversity and socio-economic wellbeing" (ManFor C.BD.), which is aimed to evaluate carbon stock in forest soils and to assess its relationships with important landscape features. The study area (33.2 hectares) is a forest beech located in the Biogenetic Nature Reserve "Marchesale" in southern Italy (Serre Massif, Calabria). It has a mean elevation of about 1,180 m a.s.l. and is geologically characterized by Palaeozoic granitoid rocks deeply fractured, weathered and frequently covered by a thick regolith and/or colluvial deposits. The morphology of the study area is dominated by a mountains landscape with deep, V-shaped valleys and summit Paleosurfaces representing the remnants flat or gently-sloping highlands, often sharply separated by steep slopes. Soils are relatively young (Entisol and Inceptisol), from poorly to moderately differentiated in relation to nature and weathering grade of parent rock and topography. Soil depth ranges from shallow to moderately deep whereas soil profiles are characterized by A-Bw-Cr and/or A-Cr horizons with the upper A-horizon characterized by a high accumulation of organic matter (umbric epipedon). The pedoclimate is characterized by a mesic soil temperature regime associated with an udic soil moisture regime. Twenty-three soil profiles were selected to be representative of all soil types and physiographic units of the study area. Each horizon of the selected horizons was described, sampled and analyzed for some chemical and physical properties (SOC, bulk density, texture and pH). Moreover, at each profile, the organic layer (O) was sampled using a metal frame of 20 cm x 20 cm and SOC content was determined. The soil samples were classified as sandy loam and loam, pH values ranged between 3.9 and 5.3, while bulk density values from 0.3 to 1.4 g cm-3. SOC of mineral horizons ranged from 9.1 g kg- 1 to 132.3 g kg-1 with a mean value of 50.1 g kg-1. In the organic horizons, SOC ranged from 111.8 to 288.1 g kg-1 with a mean value of 183.3 g kg-1. The mean value of SOC stock for all the profiles was 58.2 Mg ha-1. Taking into account the type of horizon (mineral or organic), the mean carbon stock was 5.1 Mg ha-1 for the organic horizons and 68.9 Mg ha-1 for the mineral horizons. Finally, the relationship between SOC stock and landscape features controlling SOC dynamic was analyzed and described.