Fire enhances whitebark pine seedling establishment, survival, and growth

Periodic fire is thought to improve whitebark pine (Pinus albicaulis Engelm.) regeneration by reducing competition and creating openings, but the mechanisms by which fire affects seedling establishment are poorly understood. I compared seedling vegetation production in adjacent sites, one last burned in 1880 and the other in 1988, to test the hypothesis that recent fire increases whitebark pine seedling growth. I experimentally tested effects of fire on seedling recruitment and growth by planting seeds in prescribed burned and nearby unburned sites. Experimental results showed nearly three times greater seed germination and seedling survival in recently prescribed burn plots. Seedling vegetation production in the 1880 and 1988 burn sites were measured using stem diameter and number of new needle bundles. Stem diameter was approximately 26% greater after the more recent fire in the 1988 burn site, and new needle bundle production was approximately 40% greater in this site relative to seedlings in the adjacent site that was last burned in 1880. Seedling growth, measured as both above- and below-ground biomass, was approximately 57% greater in a recently prescribed burn site relative to growth in an adjacent site that was unburned since 1910. Higher growth rates after prescribed fire corresponded with greater soil NO3- and soil-available P concentrations relative to unburned controls. However, high N concentrations in leaves of seedlings in unburned plots indicated that whitebark pine seedlings were not N-limited. Higher P, increased light availability, and earlier snowmelt after fire may be important factors in general post-fire success of whitebark pine.