What does a healthy forest look like?
There are dozens of ways you could find an answer, but Rob York has his own simple litmus test. It starts with his own question:
鈥淐an you run through it?鈥�
As he makes this ask, he gestures toward a patch of forest. To one side, a dense area. To the other, a more spacious plot where many trees are charred, some fallen over and broken apart 鈥� all evidence of the prescribed burns and other intentional tactics used to thin the area out.
Of the two, which is York鈥檚 choice for a healthy forest? It鈥檚 the spacious plot with burnt trees, he says, where there鈥檚 plenty of room for a person to, in theory, go for a light jog.
鈥淭he idea is that if it doesn't have a lot of fuel on the ground [like] sticks and logs, you should be able to run through it,鈥� he said.
Just over a couple decades ago, most researchers in California would have told you a healthy forest was one thick with vegetation, free from fire altogether.
鈥淚t was very common 15 years ago that I鈥檇 bring people here and I鈥檇 ask them, 鈥榃hat do you think? Is this a healthy forest?鈥� and they鈥檇 say, 鈥榊eah, this looks great. There鈥檚 a lot of trees 鈥� therefore, it鈥檚 a healthy forest,鈥欌�� he said.
Now, with the looming threat of wildfires, those same researchers have changed course.
York鈥檚 example is part of Blodgett Forest, an isolated area just west of Lake Tahoe. York, who is a researcher with UC Berkeley, and others like him investigate different land management techniques at the site, such as prescribed burning, which is deliberately setting a fire to clear out the area.
And with those techniques come a revised image of a healthy forest.
鈥淭hey鈥檙e green on the top and black on the bottom,鈥� York said of trees after prescribed-burning. 鈥淭o me, that does represent a sense of naturalness.鈥�
This forest is parceled out like patchwork, with different pieces of land assigned to different management techniques, in order to evaluate their effectiveness side-by-side.
Although the research in this area goes way back, beginning some time after the University of California first acquired the site in 1933, it wasn鈥檛 until the launch of a study in 2003 that researchers shifted their focus to the reintroduction of fire and, chiefly, efforts to make forest land more fire-safe.
Ariel Roughton, research forest manager for the Berkeley Forests, says this came naturally once scientists became more aware of the excess fuels in California forests.
鈥淎s the needs change, so does our management here,鈥� she said.
This was not always the priority. Over the years, different interests have ruled forest management. Timber harvests. Endangered species. Carbon storage. The list goes on.
And now researchers say that managing California鈥檚 forests means a balancing act.
鈥淚t鈥檚 really a societal question on what mix you鈥檙e able to have,鈥� said John Battles, a professor of forest ecology at UC Berkeley who鈥檚 conducted studies in the forest. 鈥淎nd then that becomes, 鈥楬ow do you balance those?鈥欌��
A recent history of forest health
To understand the dueling interests that have shaped California lands, Battles says you have to look back at the last hundred years of forest management.
He starts his retelling in the early 1900s, when state officials made fire suppression the norm. This decision meant stopping the spread of natural fires, as well as the burning practices that Indigenous communities had conducted for thousands of years.
Timber harvesting reached its pinnacle mid-century, leading to the decimation of many thousands of California鈥檚 oldest trees. This began to slow down in the 鈥�80s, when advocates for endangered species like the spotted owl vied for denser forests that provide better habitat while suppressing fires continued.
As a result, more trees survived and fuels built-up on the forest floor 鈥� like excess brush and fallen trees 鈥� since there were no fires to clear them out.
As forest density reached its peak in the 鈥�90s, new problems arose. Insect infestation, like the bark beetle, spread more easily when trees were in close proximity. And fires, of course, gained easier traction in crowded areas, as well.
Researchers began to take note of these changes. Battles says that, for him, a turning point was the Moonlight Fire in 2007. At 60,000 acres, it wasn鈥檛 massive by today鈥檚 standards. But at the time, it marked a jump in size from the fires that came before it.
鈥淭hat was already much more severe fire conditions than what we鈥檇 seen,鈥� Battles said. 鈥淲e knew back in the early 2000s that with climate change and the conditions of our forests 鈥� that we were setting things up for bigger fires.鈥�
These concerns gained enough traction to launch the in 2003, when Battles says researchers reintroduced fire to natural landscapes at Blodgett through studies that remain active to this day.
And with even larger fires seen throughout California in the past few years, he adds that attention to their work has grown.
鈥淚t鈥檚 definitely on people鈥檚 radar now as a real risk,鈥� he said.
Reimagining California鈥檚 forests today
Even in Blodgett Forest, where prescribed burning has been used for years, there鈥檚 no hope of the area returning to what it looked like a century ago.
Consider the patch of forest York used in his example of a healthy area: He says that a hundred years ago, this area of forest was one where he could expect to find larger, older trees than the ones he sees now. But after decades of relentless timber harvest, this is no longer the reality.
鈥淒espite our best efforts as managers, we can鈥檛 replace those immediately,鈥� he said. 鈥淏ut we can certainly try to work toward that, and that鈥檚 been part of the strategy.鈥�
There鈥檚 evidence of California鈥檚 shifting priorities when it comes to treating natural lands 鈥� most recently, the state鈥檚 鈥� but this is more than a money problem.
鈥淲e want to be a leader on climate change. We also want to increase our wildfire resilience in California. We also want to protect our endangered species and biodiversity 鈥� and we have to figure out how to do that,鈥� Battles said. 鈥淏ut we have to recognize that some of these goals have trade-offs, that you can't have everything in one place.鈥�
Then comes the balancing act. Roughton says that Blodgett provides a microcosmic example of what California鈥檚 forests could look like as a whole.
鈥淧art of our goal here is to be able to study them, but also to show people, show the public, what they look like and talk about the trade-offs that we have to make,鈥� Roughton said.
Their research does not mean all forest land in California should be treated the same way. Dense forests, for example, can still prove useful so long as they aren鈥檛 the status quo. Historically, they鈥檝e been particularly important in the state鈥檚 mission to reduce carbon: Since trees soak it up, they鈥檙e helpful in combating emissions.
But while dense forests can be helpful for storing carbon, Battles says they鈥檙e particularly vulnerable to wildfires, so it isn鈥檛 reliable for carbon mitigation if it can be incinerated during the next massive blaze.
Just like at Blodgett, Battles says that California can tailor its management in different areas depending on need, with fire safety being another focus along the way.
鈥淵ou clearly probably want more fire-safe forests near urban areas,鈥� he said. 鈥淚n the backcountry, perhaps that's where you can store more carbon there, and so you have those trade-offs going on.鈥�
And this balancing act is one the state must come to terms with if California鈥檚 forests are to change for the better, he says.
鈥淥ur job as scientists is to provide ways to evaluate these trade offs,鈥� he said. 鈥淓xtremes in both ways are going to be counter-productive.鈥�
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