Modeling of early stage litter decomposition in Mediterranean mixed forests: functional aspects affected by local climate

Litter decomposition is an important process affecting the carbon balance of forest ecosystems. In the Mediterranean area, seasonal changes, local climate variations and structural characteristics of forest stands may have a remarkable effect on decomposition rates. In this study, we developed a semi-empirical model for assessing the early-stage litter degradation dynamics over two years (2011-2012) in three sites located along a north-south transect in central Italy (Umbria, Lazio and Campania) and covered by sub-Mediterranean mixed woods. Adequate time-depending functions modeling the seasonal fluctuations of decomposition rates were developed and combined with suitable algorithms taking into account the effect of local climatic conditions. Leaf litter was split into the labile (easy-degraded) and recalcitrant subcomponents. The effects of temperature and moisture were modeled by specific equations and decomposition rates by time-depending functions. Equations were calibrated on field experimental data obtained by the litterbag method at the three study sites. Model validation revealed an excellent correlation between observed and predicted values (R-2 between 0.89 and 0.95), indicating the accuracy of the model in predicting differences in decomposition rates among different local climatic conditions. The simple structure and the reliability of predictions are important characteristics of the model developed, that may be considered an operative alternative to other currently used methods aimed at assessing CO2 release and carbon balance of forest ecosystems.