Sarah Dalrymple
Population Biology
Davis
She’s no anarchist, but UC Davis graduate student Sarah Dalrymple unwittingly found herself following the path blazed by the 19th-century nobleman and peaceful anarchist Peter Kropotkin.
Kropotkin’s 1902 underground classic, “Mutual Aid,” debunked social Darwinism, the idea that competition is the only law of nature that determines evolutionary success. As a young man, Kropotkin traveled to Siberia, where he noticed that rather than competing, animals often helped each other.
Dalrymple was watching ants in Australia when she had a similar insight. Just after college, she landed a plum job as a field assistant. The ants she observed in the Australian desert had a peculiar habit: They collected seeds, ate the high-protein parts, and left the rest in fertile areas where the seeds could grow. It was a win-win: Both the ant and the plant benefited.
Scientists call this phenomenon “mutualism.” Dalrymple became fascinated with these positive interactions that exist in nature, and equally fascinated by ants. As a UC Davis Ph.D. candidate in population biology, Dalrymple spends much of her time in the fire-prone Jeffrey pine forests of the eastern Sierra, where one particular species of native ant — Formica sibylla — helps fight fire by clearing pine needles from around their nests at the bases of trees.
After Dalrymple shared her research results in March at a graduate student advocacy day in Sacramento, state Sen. Ted Gaines (R-Roseville) invited her to a public forum in June commemorating the anniversary of the 2007 Angora fire that caused $141 million in damage to the area surrounding South Lake Tahoe.
Question:
Scientists talk about 'the Eureka moment' when their big idea occurred to them. But in your case, it was a question, wasn't it?
Answer:
Right. I’m in the Population Biology Graduate Group at UC Davis, and I study fire dynamics in Jeffrey pine forests in the eastern Sierra. After the Angora fire, which destroyed houses near South Lake Tahoe in 2007 and was a very costly fire, Hugh Safford, a research ecologist with the U.S. Forest Service, went in to look at the damage with a few other scientists. They noticed that in some places, trees had rings of unburned soil surrounding them. Everything else was black ash.
Question:
So they set out to solve the mystery of these rings?
Answer:
It was a mystery worth solving. They found that the trees with these ring-shaped clearings had a survival rate that was about twice as high. No one had ever really paid attention before, but Hugh and his colleagues started paying attention. They noticed ants were nesting in the tree clearings. A month or two later, I jumped in. I wanted to see what role ants might be playing.
Question:
Where did you start?
Answer:
I started exploring other Jeffrey pine forests, mostly in the eastern Sierra Nevada. I found the rings in Jeffrey pine forests throughout California, but particularly in recently burned forests. I learned that the ants clear pine needles away from the bases of the trees. If you drop a pine needle on their nest, and you wait long enough, you can see them moving it away from the entrance.
Question:
It's not something you can observe by just sitting for an hour, is it?
Answer:
No. It took me a while to figure out that the ants are most active in the early morning and early evening.
Question:
Are they just tidy little creatures?
Answer:
I think so. They just seem to prefer to nest in open areas that are free of pine needles and other leaf litter. The circles around trees might simply be a function of the fact that there are so many nests found near trees. This makes sense when you consider that they forage in the tree canopy. There are big lines of ants going up and down the tree trunk and the returning ants are often carrying food back to the nest.
Question:
Is there a larger implication in terms of mutualism, the idea that intrigued you as a student?
Answer:
I’ve spent some time investigating what ants might get out of the relationship with trees. It’s possible that they are protecting their food source from fire, but it would be hard to prove. It’s certainly safer to say that they clear the area around their nest, and saving the tree from fire is inadvertent. But we don’t know.
Question:
So ants prevent forest fires, whether they mean to or not?
Answer:
Ants can’t prevent forest fires, but they may indirectly reduce fire severity around individual trees. In ecology, there’s almost never a simple explanation.
Question:
What are the implications of your work for society at large?
Answer:
One of the things that I discovered is that these rings are almost entirely absent in places where we’ve suppressed fire for long periods of time. We’re seeing the clearings now in places where the forest service has been doing prescribed burns. If fire is removed for a long period of time, ants and other natural forces that were able to maintain the clearings become ineffective, and the clearings fill in with needles — fuel for fires.
Question:
So when the forest service does a prescribed burn, they're not only doing fire prevention, but they're administering a kind of CPR to the natural system?
Answer:
Yeah, it is pretty cool. I’ve done surveys in the Inyo National Forest near Mono Lake, where they’ve done lots of prescribed burning. The clearings become less common and smaller when you have a longer period of time between burnings.
Question:
What's the optimal period of time between burnings?
Answer:
In the sites I surveyed that had been burned 14 years ago, the trees still had clearings. So, at least 14 years. In Jeffrey pine forests near Lake Tahoe and in the Inyo National Forest, people have done studies of fire scars on trees and determined that fires were occurring every nine to 11 years before we began suppressing fires.
Question:
Does that give land managers a benchmark for prescribed burning?
Answer:
The reality is they haven’t been able to do one prescribed burn in every forest. I’ve talked to forest service people and it seems like everyone would like to do re-entries — come back to places where they’ve already burned. But there are so many forests where they haven’t even been able to burn yet — it’s not a priority. And there’s always the danger that if the conditions aren’t just right, a controlled burn can get out of control.
Question:
That's one reason people tend to resist the idea of prescribed burning, isn't it?
Answer:
People are worried, but the forest service has been doing these burns for a long time, and they’re careful. The benefits are well documented. They really do prevent those big, catastrophic fires.
Question:
How do you get that across to people?
Answer:
It was great to visit Sacramento this spring and meet with members of the legislature. Ted Gaines, who’s the state senator from the Lake Tahoe area and the eastern Sierra, invited me to a public forum on fire this June in South Lake Tahoe. In his district, where there is so much forest, it’s easy to see a connection between my research and people’s everyday lives.