The effects of post-pasture woody plant colonization on soil and aboveground litter carbon and nitrogen along a bioclimatic transect.

We investigated the effects of woody plant colonization of abandoned pastureson soil and litter organic carbon (C) stocks and nitrogen (N) content along abioclimatic transect in a semi-arid environment (Sicily, Italy). Soil sampleswere taken in three successional stages (grazed pasture, shrubland, forest)within each of three bioclimates (supramediterranean - “supra”, mesomediterranean- “meso”, thermomediterranean - “thermo”). Organic C and N in litterand soil (0-10 cm and 10-30 cm depth) were determined, as well as soil bulkdensity. Especially at 0-10 cm depth, changes in C and N contents along successionalstages differed among bioclimates. Soil organic carbon (SOC) stockdecreased from pasture to shrubland and increased from shrubland to forest in“supra”, increased from pasture to shrubland and then remained stable in“thermo”, and was stable in “meso”. Soil C/N ratio decreased with successionin “supra”, showed no significant trend in “meso”, and increased with successionin “thermo”. Litter C stock increased with succession in “meso”, increasedfrom pasture to shrubland and decreased from shrubland to forest in“thermo”, and increased from pasture to shrubland and then remained stablein “supra”. Litter C/N ratio increased in “thermo” and “supra” from pasture toshrubland and from shrubland to forest, but did not change significantly withsuccession in “meso”. The different trends in SOC among bioclimates may becaused by changes in the importance of litter input, litter decay rate and mineralization.Successional changes in “meso” and “supra” appeared to be mostaffected by litter quality, while those in “thermo” appeared to be strongly influencedby limited litter decay due to low soil moisture and high temperature.