Litter fractions and dynamics in a degraded pine forest after thinning treatments

An integrated characterization of physical, chemical, biochemical and microbiological properties of litter fractions (litter, fragmented and humified), corresponding at three decomposition phases, has been conducted in a degraded pine forest. Litter fractions were characterized in terms of C and N content, microbial communities’ structure, enzyme activities and optical properties. The objective of this approach was to give an insight of actors and mechanisms operating during decomposition process, evaluating the relationships between litter pools (organic matter and microbial communities) and activities (respiration and enzymes). The effect of different thinning treatments (traditional and selective) on litter biomass and respiration was also investigated for 2 years, to identify forest management practices aiming at increase C storage and mitigate climate change. The litter fractions showed well-distinct chemical composition, with a decrease in carbon and an increase in nitrogen as decomposition advanced. Parallelly, an increase in fungal richness and diversity, and related enzyme activities, was observed. Bacteria were similar in the three fractions but seemed to have a role in the early phase of cellulose and hemicellulose decomposition. Thinning induced a short-term increase in litter input to soil, which disappeared after the first year until determining a general decrease in litter biomass, stronger with selective thinning. Further, in the warmer months of the second year after thinning litter respiration showed an increasing trend. Overall, positive effects of thinning on C storage were evident in the short term, followed by a decrease in litter pool driven by higher litter respiration.