Water availability and the comparative emergence of four conifer species
Some conifer species require shelter from direct sunlight to establish on surface charred organic matter. Since shelter slows the rate of soil drying, it has been postulated that the emergence of seedlings on such seedbeds is limited by soil moisture availability. In the greenhouse, the emergence of four species was observed from beds of soil watered at different frequencies. Compared with well-watered controls, emergence from infrequently watered seedbeds was higher in jack pine (Pinus banksiana Lamb.) than in eastern white pine (P. strobus L.) and lowest in black spruce (Picea mariana (Mill.) BSP.) and the balsam fir (Abies balsamea (L.) Mill.). This is in the same order as the ability to emerge without shelter on postfire seedbeds. Coping with fluctuating moisture availability was concluded to be a major factor in determining emergence on this harsh seedbed. Seeds were also germinated in solutions of polyethylene glycol 6000. These data, together with measurements of the resistance to and tolerance of water loss, suggest that eastern white pine succeeds because preemergent seedlings can tolerate desiccating conditions. Measurements of radicle elongation rates indicate that jack pine succeeds by evading periods of low water availability.