The effects of seed source health on whitebark pine (Pinus albicaulis) regeneration density after wildfire

Whitebark pine (Pinus albicaulis Engelm.) populations are declining nearly rangewide from a combination of factors, including mountain pine beetle (Dendroctonus ponderosae Hopkins, 1902) outbreaks, the exotic pathogen Cronartium ribicola J.C. Fisch. 1872, which causes the disease white pine blister rust, and successional replacement due to historical fire exclusion practices. With high mortality in cone-bearing whitebark pine, seed production may not be sufficient to support natural regeneration after disturbance such as wildfire. Our objective was to examine the relationship between whitebark pine seed source health and whitebark pine regeneration density in adjacent burns. We sampled regeneration and seed source health in 15 burns within six national forests and three Wilderness Areas in Montana, ranging from 5 to 23 years old. We found a significant, positive relationship between seed source health and seedling density in adjacent burns. Natural regeneration was sparse when the proportion of damaged or dead whitebark pine in the seed source exceeded 50%. Factors that influenced the presence of whitebark pine regeneration within a burn included both vegetation cover and potential solar radiation. Sites closer to seed sources had higher probabilities of seedling occurrence, but seedlings were present throughout most burns. Our results suggest that managers can prioritize restoration plantings of whitebark pine seedlings after wildfire based on the health status of the nearest seed sources.