Spatial patterns of soil microclimate, light, regeneration, and growth within silvicultural gaps of mixed tolerant hardwood – white pine stands

Abstract

Large gaps (equivalent to twice the height of the trees, 1590 m2) originating from group selection cutting in mixed tolerant hardwood – eastern white pine (Pinus strobus L.) stands of Quebec were used for geostatistical analysis of the seasonal mean of daily percent photosynthetic photon flux density (%PPFD), soil temperature and moisture, regeneration density of white pine, yellow birch (Betula alleghaniensis Britt.), and paper birch (Betula papyrifera Marsh.)), and growth of white pine. %PPFD, which measures the quantity of light above the shrub layer, varied according to the north–south axis, the maximum being located in the northern portion of gaps. Surficial soil (5 cm) temperature and moisture varied according to both north–south and east–west axes. The southwest sector offered favourable conditions for white pine, yellow birch, and paper birch establishment, with maximum soil moisture and minimum soil temperature encountered in this position. There was no evidence of gap partitioning at the early establishment stage, although asymmetry in the microclimate was observed. However, results indicate that spatial patterns could change in the future and a partition resulting from differential survival among species could occur. Finally, results outline a possible discordance between optimal regeneration and growth niches for white pine, since planted seedlings (>1 m) had the best growth in the central and northern section of gaps.