The triple threat: bark beetles, disease, and fire

Over twenty years ago, two intrepid park scientists, Dan and Cynthia Duriscoe, set out on a seemingly impossible mission: install 154 long-term monitoring plots in some of the most remote wilderness in the lower 48. Their goal was to establish a scientific baseline for a highly infectious disease, white pine blister rust (Cronartium ribicola), in Sequoia Kings Canyon National Parks (SEKI). The tree disease was accidentally introduced into the US over 100 years ago. One source of invasion stemmed from Gifford Pinchot—the father of conservation—who unintentionally ordered infected seedlings from Europe for reforestation. The disease spread rapidly throughout the US, leading to the candidate listing of whitebark pine under the Endangered Species Act.

With the help of fearless crew, helicopters, pack horses, and a healthy dose of grit and determination, the Duriscoe team succeeded. Hoping a few adventurous souls would follow in their footsteps, the team left two hand-written journals with directions on how to find the plots. Each plot was marked by small, half-dollar-sized metal monuments they had drilled into random rocks throughout the parks (Photo 1).

Almost twenty years later, a second group of scientists embarked on the adventure of a lifetime. Between 2015-2018, I led a team that resurveyed the Duriscoe plots and together, we found the exact same trees that were measured twenty year earlier. Sometimes it took us three days to find the tiny plot markers, but with patience, persistence, and a lot of mountaineering, we found every single plot. After we laid the transects, a flurry of activity ensued, as we searched each tree for signs and symptoms of white pine blister rust (blister rust) mountain pine beetle (MPB; Dendroctonus ponderosae) and fire (Photo 2).

The most concerning finding was that sugar pine are declining in SEKI at a much faster rate than previously documented. Over the past twenty years, we lost 52% of the plot trees due to a combination of blister rust, MPB, and fire. Sugar pines are arguably the largest pines in the world and their losses will have cascading impacts on forest function and wildlife habitat. We also saw concerning mortality patterns in western white pine. These beautiful trees saw the largest increase in blister rust over the past twenty years, which has long-term consequences for the population’s stability.

Here’s the good news: the high elevation, subalpine forests in SEKI are relatively healthy (Photo 5). Foxtail pine, a species closely related to bristlecone pine, remained blister rust-free. While we found a few infections outside of the plots, foxtail was mysteriously resistant to infection. We also found blister rust infections in whitebark pine for the first time; however, the prevalence remained low. Finally, MPB attacks occurred across all four species, but these attacks dropped precipitously in high elevation whitebark and foxtail pines. Whether these patterns will persist under climate change remains and outstanding question that we explore in another paper currently in review. Stay tuned.

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