Exploring litter decomposition dynamics in Mediterranean pine forests

Forests’ global carbon stock is estimated at 662 Gt, with 45% of it being soil organic matter (FAO 2020). Mediterranean forests, while crucial for long-term carbon storage in their soils (with a reported 25% of CO 2 assimilated through photosynthesis being stored in the ecosystems’ soils (Luyssaert et al. 2007), face growing threats from climate change-induced xerothermic conditions and ongoing anthropogenic disturbances. Even though climate change mitigation strategies in forestry have been developed, they mostly concern wood and biomass production, and less attention has been given to mitigation strategies regarding forests’ soil carbon stocks in Europe. PineOptim project attempts to investigate the impact of different management practices on water and carbon budgets in pine forests, across an established monitoring network of Pinus brutia and P. halepensis forests distributed across Sani, Xanthi and Lesvos Island in Greece. This study, as part of the PineOptim project aims to enhance current knowledge on decomposition dynamics in Mediterranean forests and the effects of abiotic factors involved under different management regimes, vegetation status and climatic regions. The study areas in Sani ( P. halepensis with evergreen understory vegetation) and Xanthi ( P. brutia with broadleaf tree understory) have been subjected to various management practices (understory removal in Sani and different overstory thinning intensities in the peri-urban forest of Xanthi), while on Lesvos the study area consists of unmanaged P. brutia stands varying in post-fire age and stand structure density. Decomposition dynamics have been studied by a parallel implementation protocol of the litterbag method and a standard materials method (paper sheets and wood sticks) (Kurz-Besson et al. 2005; Joly et al. 2017) for evaluating site-specific physicochemical litter characteristics drivers along with micro-environmental factors. Analysis was conducted using generalized linear and non-linear mixed effects models, to explore the importance of each factor involved in decomposition dynamics across and among the various study sites. Preliminary results suggest a significant influence of atmospheric and soil climatic parameters (air relative humidity, soil temperature and water content) and their interaction, along with Leaf Area Index (LAI) to decomposition rates and the remaining organic mass. Regional deviations are highlighted, giving us insight into the rates of organic matter assimilation under each management practice and climatic region. These findings underscore the potential of tailored forest management strategies to optimize litter decomposition and soil carbon stocks, in mediterranean pine forests. In addition, our results support the integration of decomposition dynamics into climate change mitigation strategies on the forestry sector.