Drivers of litter dynamics across Spanish forests: An assessment using ICP-forests Level I monitoring data

Résumé fourni par la source

Litter stocks account for approximately 8.7 % of total carbon stocks in European forests, playing a crucial role in nutrient cycling, carbon storage, and forest ecosystem health. This study analyzes the climatic, environmental, and structural drivers of litter accumulation and quality in Spanish forests across four bioclimatic regions. Using data from 620 plots monitored through the ICP Forests Level I network over three measurement cycles (2014–2024), we evaluated spatial and temporal patterns of litter biomass and quality using Generalized Linear Mixed Models. Our results show the highest litter stocks in the Atlantic bioregion, especially in mixed conifer-broadleaf forests, (up to 11.21 ± 7.7Mg ha⁻¹), while significant declines were observed over the time span considered in Subalpine and Montane Conifer and Deciduous Broadleaf forests. The Mediterranean region also displayed high litter stocks but with marked declines. In contrast, the Alpine and Macaronesian bioregions showed no significant changes. Litter quality, assessed via C/N ratios, varied substantially among regions and forest types. The Mediterranean region displayed both the highest mean C/N values and the widest range, particularly in coniferous and mixed stands. Significant temporal declines in C/N were observed in the Mediterranean, Alpine, and Atlantic regions. Overall, litter dynamics were driven by a combination of factors, including mean tree age, climatic variables, forest types, bioregion and site conditions. The study provides statistical indications of a decline in both litter stocks and C/N ratio over the past 11 years, emphasizing the need to integrate spatial and ecological variables to better understand forest litter dynamic. • Litter dynamics are shaped by bioregion, forest type, and spatial-climatic factors. • Litter stocks declined significantly in Spain's forests over the past 11 years. • Atlantic forests showed the highest litter stocks, especially mixed forest types. • C/N litter ratio varied significantly among the forest types studied. • C/N ratios declined over time in Mediterranean, Alpine, and Atlantic regions.

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