Catherine Larouche

Northern white-cedar (Thuja occidentalis L.) is an important commercial species with a high wildlife value, both as a food source and habitat for many bird and mammal species. Concerns have been expressed about its decreasing abundance across its range, and especially in mixedwood stands, where it has to compete with several other species and can suffer from heavy browsing. In this study, we quantified the development of natural northern white-cedar seedlings and saplings under various partial cutting regimes, with and without white-tailed deer (Odocoileus virgianus Zimmerman) browsing, in three selected sites in Quebec (Canada) and in Maine (USA). Our data show that northern white-cedar regeneration was present in all studied stands, but that only a few stems were taller than 30 cm on the two sites with high densities of deer. In the absence of heavy browsing, stems reached a height of 30 cm in 11 years, and 130 cm in 28 years. Height growth of northern white-cedar regeneration increased with canopy light transmittance, while ground-level diameter increment increased after partial cutting. This suggests that partial cutting can be used in mixedwood stands to release natural northern white-cedar regeneration, but also that the recruitment of northern white-cedar seedlings to larger size classes constitutes a major challenge in stands subject to heavy deer browsing.

The use of clearcutting involves the creation of exposed edges that become vulnerable to windthrow. The spatial distribution of cutblocks can influence the level of damage. This study compares windthrow losses at edges of clearcuts for two spatial distributions of clearcuts in the balsam fir-white birch ecological domain. The level of windthrow was estimated from aerial photographs of five year-old clearcuts. The proportion of windthrow in the first 30 m of edges around clearcuts amounted to 20.4% for grouped clearcuts in comparison with 15.8% for dispersed clearcuts. Dispersed cutting did not modify the level of damage per unit length of edge. However, the greater perimeter for a similar cut area in the dispersed pattern led to a greater amount of damage per area harvested (15.99 vs. 6.34 m³·ha^-1). Key words: windthrow, logging edges, landscape patterns, grouped clearcut, dispersed patch cutting, balsam fir