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Facing Fire - Greenler Living Amidst Wildfires, Studying Prescribed Fire

Photo Credit: Will Harling

Master’s degree alumna Skye Greenler has been up close and personal with fire before in her studies of prescribed fire in relationship to oak regeneration. Recently, Greenler, a 2018 forestry alum, has been living amidst a completely different kind of fire while working on her PhD in Corvallis, Oregon. Her previous experiences give her a unique perspective on the nearby wildfires and only deepen her drive to study the effects of fire on the local landscape.
Will Harling Slater Fire.
Photo Credit: Will Harling

“My partner (Graham Frank, another Purdue grad alum) and I are feeling safe in Corvallis, but are experiencing lots of smoke, watching places we love and work burn, and supporting friends and family who have evacuated,” Greenler shared. “Fire scientists have been predicting an event like this for years, but that does not make it any more extraordinary or sobering to witness. The sheer number of acres burned, number of homes and communities lost, and likely number of lives lost is hard to really comprehend. Just yesterday (Sept. 9) alone over 500,000 acres burned in Oregon and Washington. Luckily the strong easterly winds have just died down and fire behavior should correspondingly become more manageable.”

Although devastating, Greenler is quick to note that in the Western United States, fire is a natural process that is foundational to maintaining ecosystem health and resilience, but methods of management must be addressed.

“These events are a clear indication that current fire management and policy is not working and it’s time for an overhaul to simultaneously reduce the risk of uncharacteristic, destructive fires, while promoting natural fire and forest processes that are critical to restoring forest resilience and reducing long-term risk,” she said. “Right now, it is hard to know details about the effects of the current fires. Large climate- driven events like these tend to produce large areas of high severity, but there likely are also areas within the fires where effects are more moderate and have ecological benefits.”

Regardless of the outcomes of the current wildfires, Greenler is committed to being part of the solution. She recently received a grant to develop landscape-scale fire models that incorporate Indigenous fire management practices into cutting-edge fire risk and ecological modeling tools for a landscape in the Klamath Mountains of Northern California. The work is part of a large collaborative effort with tribal experts, resource managers, local nonprofits and scientists to better understand historical forest conditions, implications of different management decisions, and changes necessary to build future climate and wildfire adapted ecosystems and communities.
Greenler Corvallis Smoke
Photo Credit: Skye Greenler

“Unfortunately, our study landscape is currently burning in the Slater Fire and local partners and tribal collaborators are watching thousands of acres burn that they have been actively trying to treat with prescribed fire and cultural burns for years but have been met with resistance from federal agencies,” Greenler said. “It’s too early to know how it will affect our work, but it’s sobering to watch.”

Greenler recently published two articles from her master’s degree studies on prescribed fire, “Prescribed Fire and Partial Overstory Removal Alter an Acorn-Rodent Conditional Mutualism” (published in Ecological Applications) and Prescribed Fire Promotes Acord Survival and Seedling Emergence from Simulated Caches” (published in Forest Ecology and Management), both co- authored with advisors Dr. Rob Swihart and Dr. Mike Saunders at Purdue.

In a nutshell, Greenler’s work spotlighted the work of squirrels in assisting with oak regeneration after a prescribed fire. She assessed different factors that influence oak regeneration from acorns and the establishment of new seedlings and explored how forest management intended to promote oak regeneration influenced how squirrels and other rodents interacted with acorns.

Greenler explains the background for this research.

Skye Greenler shoulder headshot.
“Squirrels and some other rodents display what scientists hypothesize is a conditional mutualism with oaks and acorns,” Greenler said. “Squirrels can negatively affect oak regeneration by eating acorns, but they can also help oak regeneration by moving acorns away from the parent tree and burying them in a small cache to store for later, but never retrieving them—that’s the mutualism part, squirrels help oaks and the oaks help squirrels. The conditional part means that how much squirrels help or hinder oak regeneration is dependent on the environmental conditions. A different set of scientists have been working on a hypothesis they call the oak-fire hypothesis, which suggests that low intensity fire helps promote oak establishment and dominance. Until our research these two hypotheses were only considered separately—scientists either thought about how forest conditions affected the relationship between squirrels and acorns/oaks or how fire helped oak regeneration but never considered if fire influenced how helpful or harmful squirrels were to oak regeneration.”

Greenler and company conducted three experiments to see how fire influenced the interactions between squirrels and acorns.

First, they did two experiments to see if prescribed fire affected overwinter survival for acorns that were just on the forest floor and for acorns that were buried in shallow holes that mimicked squirrel caches—because squirrels are notorious for pilfering each other’s caches and eating the acorns. In both of these experiments, they found much higher acorn overwinter survival in the burned sites than in the unburned sites—the odds of acorn survival were 1.4-2.1 times higher in the burned areas. For the cached acorns they analyzed what vegetation characteristics were associated with higher acorn survival and found that both how much vegetation cover there was in the three feet above the ground and how much dead wood there was on the forest floor were very important—both things that can be strongly influenced by prescribed fire.

These experiments, which Greenler conducted collaboratively with undergraduate Lara Estrada, also looked at how canopy harvest gaps influenced acorn survival and found that acorns had higher survival outside of harvests on the forest floor, especially in burned sites, but there was no effect of harvest for cached acorns.

Although the group had made discoveries with regards to acorn survival after a prescribed fire, they wanted to assess if acorns could survive through a prescribed fire, potentially debunking a theory from forest managers who worry that prescribed fires will kill their acorns.
Sky Greenler spraying for controlled fire burn, MS research.

In the third experiment, the group conducted 8 prescribed burns over a two-year period to assess the survival of red and white oak acorns that were on the forest floor or in shallow holes that mimicked squirrel caches in both fall and spring prescribed burns. Many past studies have shown that uncached acorns on the soil surface rarely survive the winter and they found the exact same thing: only 6 of the 480 acorns on the forest floor survived to germinate in the spring and all were in one of the burn treatments, none were in the unburned control. The acorns in the artificial caches showed even more surprising germination results, acorn germination was 3.4-12.1 times higher in the burned sites than the unburned control. Both years they found that, by far, the highest germination occurred for acorns that had been cached in an area that was then burned. They also found that red oak acorn survival was higher after fall burns than spring burns, but there was no difference between burn seasons for white oak.

“These three experiments together suggest that we don’t just have decreased vegetation competition and increased light to thank for oak regeneration after fire, but also, potentially, squirrels,” Greenler explained. “This is interesting because it helps us understand one way that management influences oak regeneration, and also links two ecological hypotheses that were previously only considered separately. These were the first experiments done to look at these interactions. More work on the interactions between fire, squirrels, and acorns will help us understand how strong these effects are, if they happen across the region or just in Central Indiana, and how long they last after a prescribed burn. For now, we think it’s fair to add changing squirrel behavior and acorn survival interactions to the growing list of reasons prescribed fire benefits oaks.”

Skye Greenler checking forest ground, MS research.
Greenler’s experience with prescribed fire, including a 10,000 prescribed burn she was a part of in Oregon last year, made her a great resource and guest lecturer for Purdue Extension wildlife specialist Jarred Brooke to tap into in the spring when COVID-19 hit and prevented him from getting his fire ecology class out in the field to do prescribed burns. (When Best Laid Plans Go Up In Smoke)

“Prescribed fire is something that sometimes can be unpopular or tricky to implement, but the more we understand about its benefits and how fire shaped the ecosystems we know and love today, the more public support and funding there will be to use fire as a management tool and reintroduce natural disturbances back into our ecosystems,” Greenler shared. “While acorn survival to germination is only one of many steps to oak establishment and oak forest restoration, past research has shown it’s a very important one. If fire can help double (or 12x!) acorn survival to germination, it could help set forests on a path to a future where oaks are a dominant species and managers can continue to use ecological forestry methods to promote healthy, ecologically robust, culturally desirable, and economically valuable forests.”

Once the fires subside in Oregon and in northern California where Greenler’s current research is taking place, she is anxious to get out and assess the impacts of the wildfires and contrast them with those of prescribed fire and do her part to prevent future outbreaks.

To glimpse the spread of the current wildfires, visit the Wildfire Early Notification Map.

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