Effect of sowing date on the germination and establishment of black spruce and jack pine under simulated field conditions

Abstract

We used a diurnally and seasonally realistic simulation of seedbed conditions in a controlled environment chamber to test the dependence of seedling growth during the first year on the timing of spring germination in jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] BSP.). Jack pine germinated poorly under cold, early season conditions compared to black spruce. Survival in seedlings that did emerge was high and fairly constant through the early season in jack pine, and increased steadily as the season advanced in black spruce. Subsequent seedling development, measured as time to shedding of the seed coat, was slowed more by early season conditions in jack pine. Earlier emerging seedlings in both species achieved greater total biomass growth through the simulated season; jack pine seedlings consistently grew more than black spruce for all sowing dates. Height growth changed little with time of seedling emergence for jack pine, but increased greatly in earlier emerging black spruce. These results suggest that early season events can be important determinants of conifer seedling establishment and may help to explain the geographic limits of these two widespread boreal trees.