Régénération, compétition, croissance et variation spatiale à l'intérieur de trouées issues de coupe dans un peuplement de feuillus tolérants à pin blanc

The general objective of this research was to study the effects of group selection on white pine (Pinus strobus L.) regeneration, growth, spatial variation and initial succession dynamics in tolerant hardwood-white pine stands. An experiment comparing group selection (45 m diameter, 2H gaps H = stand height) to single-tree selection cutting (25% and 35%) was carried out near Maniwaki (Quebec, Canada) in 1998. Monitoring of soil microclimate, regeneration, competing vegetation and white pine growth (natural and planted) was done during the three following years. A retrospective study of gaps originating from diameter-limit cutting (1972–1976) examined the long term effects on white pine growth, competitive status and health. The 2H gaps, combined with scarification, resulted in the successful establishment of white pine, yellow birch (Betula alleghaniensis Britton) and paper birch (Betula papyrifera Marsh.). Light environment in gaps was more favourable to white pine growth, with 50 ± 12% light under the shrub layer (vs. 8 ± 1% and 11 ± 5% in the single-tree selection). However, the microclimate and the abundant competition restricted the three species establishment to the border and south of gaps, while the optimal growing conditions were found in the centre and north. The retrospective study showed that gaps having a diameter smaller than 0,7H contained no merchantable white pine stem after 25 years. Gaps larger than 1H had a higher, but acceptable, defective stem proportion (<14%). In the light of results, two strategies may be considered to maintain white pine presence in tolerant hardwood stands and to avoid a release treatment of natural regeneration: (i) create smaller gaps (0,7–1H) to improve natural seedlings microclimate and to reduce competition; (ii) use large stock seedlings to grow white pine under partial canopy in large gaps (2H).