Spatial and temporal patterns of seedling and sapling recruitment within canopy gaps caused by spruce budworm

Abstract

Gap dynamics theory suggests that spatial and temporal patterns of species recruitment within canopy gaps may be due to differences in shade tolerance. Although this theory has been developed in low latitude forests, we suggest that it is also applicable in boreal forests. This study investigates temporal and spatial patterns of seedling and sapling regeneration in canopy gaps caused by spruce budworm. Tree seedlings, saplings, and shrubs were mapped, measured, and aged in five gaps in a 234-year-old conifer stand in the southern part of the boreal forest. Shade-tolerant fir and cedar seedlings and saplings were found in the southern part of the gaps, whereas intolerant aspen root suckers were associated with the northern part of the gaps. Within gaps, fir seedling and sapling density at the quadrat scale was negatively related to mountain maple cover. A temporal partitioning of seedlings and saplings into pre- and post-gap formation also showed a gradient of species establishment related to shade tolerance. The zone of high light in the northern part of large gaps may permit the maintenance of shade-intolerant species in these forests. However, the small area of this zone and the slowness of gap formation will limit shade-intolerant species abundance.