Assessment of Leaf Litter Decomposition in a Pine and Beech Mixed Forest: Case Study in Northern Spain

Abstract

The promotion of mixed forests represents an adaptation strategy in forest managementto cope with climate change. The mixing of tree species with complementary ecological traits maymodify forest functioning regarding productivity, stability, or resilience against disturbances. Litterdecomposition is an important process for global carbon and nutrient cycles in terrestrial ecosystems, also affecting the functionality and sustainability of forests. Decomposition of mixed-leaf litters has become an active research area because it mimics the natural state of leaf litters in mostforests. Thus, it is important to understand the factors controlling decomposition rates and nutrientcycles in mixed stands. In this study, we conducted a litter decomposition experiment in a Scotspine and European beech mixed forest in the province of Navarre (north of Spain). The effects offorest management (i.e., different thinning intensities), leaf litter types, and tree canopy on massloss and chemical composition in such decomposing litter were analysed over a period of threeyears. Higher decomposition rates were observed in leaf litter mixtures, suggesting the existence ofpositive synergies between both pine and beech litter types. Moreover, a decomposition processwas favoured under mixed-tree canopy patches. Regarding thinning treatments significant differences on decomposition rates disappeared at the end of the study period. Time influenced the nutrient concentration after the leaf litter incubation, with significant differences in the chemical composition between the different types of leaf litter. Higher Ca and Mg concentrations were found inbeech litter types than in pine ones. An increase in certain nutrients throughout the decompositionprocess was observed due to immobilization by microorganisms (e.g., Mg in all leaf litter types, Konly in beech leaves, P in thinned plots and under mixed canopy). Evaluating the overall responsein mixed-leaf litters and the contribution of single species is necessary for understanding the litterdecomposition and nutrient processes in mixed-forest ecosystems.