Effects of tree species and clear-cut forestry on forest-floor characteristics in adjacent temperate forests in northern Spain

The litter layer (L) and fermented humified layer (FH) in forest floor under European beech (Fagus sylvatica L.), pedunculate oak (Quercus robur L.), and radiata pine (Pinus radiata D. Don) were studied in northern Spain. Recovery from heavy mechanization was also assessed in a chronosequence from two adjacent pine plantations (3 and 16 years old). Interspecific differences in forest-floor mass and mass distribution were related to litter quality and decomposition rates. In the L layer, acid-insoluble residue/N, C/N, and C/P ratios were lower, and pH and Ca contents higher in the deciduous stands than in the pine stand. The microbial respiration rate was higher and functional diversity lower in the pine stand than in the deciduous stands, without differences in microbial biomass. Cross-polarization, magic angle spinning C-13 nuclear magnetic resonance and proximate analysis revealed similar C functional groups in beech and pine stands. Forest floor was still absent 3 years after heavy mechanization, and after 16 years, it was 50% less abundant than in the mature stand. Microbial respiration rate, biomass, and diversity were similar in the L layer in 16-year-old and mature pine stands, but in the FH layer, microbial-community diversity remained low after 16 years. The results underline the effects of forest management on C transformations in the forest-floor layers. These effects may be evident even after 16 years of heavy mechanization.