The effects of seed source health on whitebark pine regeneration density after wildfire

Whitebark pine (Pinus albicaulis) is declining nearly range-wide largely from mountain pine beetle (Dendroctonus ponderosae) outbreaks and the exotic pathogen Cronartium ribicola, which causes the disease white pine blister rust. With high mortality in cone-bearing whitebark pine, seed production may not be sufficient to support natural regeneration after disturbance such as wildfire. The objective of this study was to examine the relationship between whitebark pine seed source health and whitebark pine regeneration density in adjacent, stand-replacing burns. I sampled regeneration patterns and seed source health and status in 15 burns within six national forests and three Wilderness Areas in Montana, ranging from five to 23 years old. I found a significant, positive relationship between seed source health and seedling density in adjacent burns. Natural regeneration was sparse when the proportion of infested or dead whitebark pine in the seed source exceeded 50%. Fine-scale factors that influenced the presence of whitebark pine regeneration within a burn included both vegetation cover and potential solar radiation. Sites closer to a seed source had higher probabilities of seedling occurrence, but seedlings were present throughout most burns. These results suggest that managers can prioritize where to plant rust-resistant whitebark pine seedlings after wildfire based on the health status of the nearest seed sources