| Commercial thinning is a silvicultural treatment that aims regular forest. To respond to socio-economic and ecosystem issues, this intervention, combined with small openings, would initiate a conversion to an irregular structure, closer to the pre-industrial forest. The main goal of this study is to investigate the forest soil nitrogen cycling in response to commercial thinning and canopy gaps. In a 30 years old balsam fir (Abies balsamea) stand, we used replicated 0. 75 ha plots within uncut forest and within commercially thinned forest, both combined with openings of 0.05 ha or no openings. Two incubation experiments were set out in June and August 2009, following the commercial thinning that took place in November 2008. In each of the treatments, we measured concentrations of dissolved organic nitrogen (DON), ammonium (NH/ 4+) and nitrate (N03- ) before and after 8-weeks in situ buried bag incubations of forest f1oor and mineral soil samples. The main forms of available N in the soil are, in order, DON and NH4 followed far behind by N03. The most noticeable changes following treatments were observed in the openings and to a lesser extent in the commercial thinning (not significant tendencies). It results in an increase in N mineralization and an increase in mineral N proportion (N03- and NH4+) relatively to DON. Our results suggest that these changes are caused by the increase in soil temperature and water content. These findings would contribute to optimize our management strategies regarding partial cuts or small scale clearcuts. Also, they will help to better understand the processes involved in the establishment of forest regeneration and vigor of competitive species. |
