Effects of a clear-cut on the in situ nitrogen mineralisation and the nitrogen cycle in a 67-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation

In situ net nitrogen mineralisation, deposition, uptake and leaching fluxes were determined in a 67-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) plantation in the Beaujolais mountains. Measurements were performed during five years before the clear-cut of the stand and two years after the clear-cut. Deposition and mineralisation of N decreased after the harvest. The drastic decrease in tree N uptake was counteracted by the developing understorey vegetation. Microbial immobilisation, favoured by the input of organic matter and the increase in temperature, was probably the cause of a decrease in the net mineralisation of N. Leaching of mineral N at 15 cm depth decreased after the harvest. However, fluxes of Mg and Ca leached at 60 cm depth did not vary after the harvest.