WHITEBARK NOISE
“One of the greatest threats to ecosystems today is anthropogenic climate change,” said Dr. Joan Dudney at the Sierra Nevada Aquatic Research Laboratory (SNARL) Tuesday night. An Assistant Professor of Global Change Ecology at the Bren School and the Department of Environmental Studies at the University of California Santa Barbara, Dr. Dudney was invited to speak as part of SNARL’s guest lecture series.
“With climate change, we’re seeing increases in average temperatures and we’re also seeing increases in the severity and frequency of droughts,” said Dudney. “But, not all forests are experiencing the effects of climate change in the same way.”
Back in 2015, Dr. Dudney was driving through Sequoia & Kings Canyon National Park. She took a photo. And then another. And then another. According to the doctor, there was not a single shot that didn’t show huge mortality events; the devastating loss of trees attributed to what, at that point, had been a 3-year long drought.
But then, about a thousand feet above, in elevation, the forest was thriving.
“It was as if there was nothing wrong. As if their neighbors down below didn’t matter,” said Dr. Dudney. “And [the trees] were actually able to grow more, and totally ignore the fact that this was one of the most unprecedented drought events we’d seen in the last 300 years.”
So it got the doctor thinking. Are high elevation forests actually going to fare better, because of climate change?
Dr. Dudney’s research has a particular focus on the whitebark pine—a tree that recently garnered the distinction of having a spot on the endangered species list. According to Dudney, whose research spans more than a decade, the whitebark pine’s vulnerability to climate change can be estimated by “quantifying the magnitude of change, multiplied by the adaptive capacity of the population.”
It’s Resilience Theory, defined by the International Panel on Climate Change (IPCC) as “ The capacity of … environmental systems to cope with a hazardous event, trend or disturbance, responding or re-organizing in ways that maintain systems’ essential function.”
To understand this ecosystemic call and response phenomenon, Dr. Dudney’s team sampled 27 plots across the Sierra Nevada, from northern Tahoe to southern Sequoia National Park, capturing a range of environmental conditions.
And importantly, because the Eastern Sierra is characterized by its unique topography and range of microclimatic conditions, it’s a crucial case study for understanding the broader impacts of climate change on whitebark pine. This region, with its mix of high-altitude environments and varied microclimates, offers a natural laboratory for observing the effects of rising temperatures and shifting precipitation patterns. Dr. Dudney describes it as a near factorial design; imperfect because the research makes use of an observational data set (Those of us that remember our high school science may recall that observational research is rife with confounding variables). Still, the team captured the extremes of both cold and wet, and hot and dry environs. Over the course of two years, Dr. Dudney’s team collected 772 tree cores and over 1,300 needles, conducting over a thousand stable isotope measurements to analyze the data comprehensively.
The research revealed that, over the past 40 years, the Sierra Nevada has experienced a 0.4°C increase in average temperatures. This warming has had a generally positive effect on whitebark pine growth, but with a nuanced, nonlinear relationship. In the colder regions, temperature increases have boosted growth, while in hotter, drier areas, growth has declined. Projections suggest that by 2099, about 20% of the whitebark pine population could experience growth declines, particularly in the Eastern Sierra.
A keystone of Dr. Dudney’s research is the concept of spatial synchrony, where populations across different areas respond similarly to environmental changes. Higher spatial synchrony often indicates vulnerability to widespread disturbances. The study found that climate change has increased spatial synchrony in whitebark pine populations, suggesting a heightened risk of mortality and biotic attacks.
Returning to Dr. Dudney’s hypothesis, what that means is that, while high-elevation forests might be less affected by direct temperature increases, their adaptive capacity is lower due to energy limitations. And that reduced adaptive capacity, like a bad immune system, is precisely what will handicap the whitebark from bouncing back in the case of significant environmental disturbance.
And those are just the direct impacts of climate change.
Dr. Dudney also explored the indirect effects of climate change, particularly the role of biotic agents like bark beetles and the pathogenic white pine blister rust.
“Mountain pine beetle, the most aggressive pine beetle, has decimated populations in northern parts of the whitebark pine range,” she said, showing images of trees with pitch tubes, a sign of their struggle to fend off beetle attacks. White pine blister rust, an invasive disease introduced in the early 1900s—ironically and accidentally by way of the Father of Conservation, Gifford Pinchot—poses a significant threat by infecting tree branches through needle stomata and often leading to tree death.
Historically, these biotic agents have been less prevalent in the southern Sierra Nevada. But, climate change appears to be shifting their range.
But, explained, Dr. Dudney, “Even though the range has expanded, the number of infections is declining in this system,” she explained.
That paradox is due to differing drought responses: while lower-elevation trees like sugar pine photosynthesize less during droughts, high-elevation whitebark pines increase their photosynthesis, inadvertently making them more vulnerable to infection during the fall when the rust spreads.
She highlighted the importance of resin production in defending against biotic agents.
“Resin is produced whenever there’s a bark beetle attack, disease, or physical damage,” explained Dr. Dudney, and a 2023 study showed that whitebark pine is capable of producing more resin over time, indicating some level of phenotypic plasticity. “This means these populations can somewhat respond to changing environments by defending themselves better.”
There is a need, says Dr. Dudney, for comprehensive, multi-faceted research and conservation efforts: consistent scientific study and monitoring practice, and practical on-the-ground actions like assisted migration and genetic testing for disease resistance. Planting whitebark pine in cooler, higher-elevation areas or in regions with more stable water availability could help ensure the species’ survival. And identifying markers in trees that are resistant to diseases to guide replanting and restoration efforts.
All of it, says the doctor, will require collaboration between universities, government agencies, non-profits, and the communities that call these ecosystems home practicing good stewardship.
