DEVELOPMENT OF SOFTWOOD STANDS AND MIXED STANDS DURING THE 30-YEAR PERIOD AFTER MECHANICAL CLEARCUTTING

This paper presents results from a 30 year monitoring of 15 clearcut a reas. Study areas were located before cutting in stands having an abun dant advance regeneration. Four study areas were initially dominated b y black spruce, four by balsam fir, three by jack pine and the last fo ur comprised a mix of species. Stand inventories and regeneration surv eys were conducted before harvesting. Harvesting was done in regular l ogging operations, without any special care to protect the advance gro wth. Regeneration surveys were taken again after harvesting, 5 years, 10 years, 20 years and 30 years after harvesting. Black spruce stands regenerated to black spruce dominated stands. Balsam fir, which was so metimes abundant in the advance regeneration, did not invade the stand s and the abundance of hardwoods was temporary. In some cases a reduct ion in yield is to be expected. In balsam fir stands, hardwoods were m ore aggressive. A reduction in softwood yield is predicted for three o f the four cutovers. The presence of a tall regeneration seems to lead to higher yields in black spruce and balsam fir stands. The evolution of jack pine and mixed stands is quite variable. In some jack pine st ands, hardwoods will constitute a significant component of the new sta nd. In some mixed stands, softwoods are not very abundant whereas in o thers they form an important part of the stand at 30 years. This study has shown an urgent need for a better understanding of stand dynamics in young stands. Such an understanding is necessary for an adequate f orecast of the yield of second growth stands.