Thinning makes forests healthier, according to research from Oregon State University

Forest thinning improves the health of older trees and enhances native biodiversity on federal lands in Eastern Oregon. That’s according to a new study from Oregon State University, in partnership with local groups in Oregon’s Blue Mountains. We talk to James Johnston, the assistant professor in the College of Forestry at OSU who authored the study, about how selective thinning could make forests more resilient in the face of wildfires.

Note: The following transcript was created by a computer and edited by a volunteer.

Dave Miller: From the Gert Boyle Studio at OPB this is Think Out Loud. I’m Dave Miller. In 2014 and 2015, loggers selectively cut some trees on over 7,000 acres in the southern Blue Mountains of the Malheur National Forest. It was part of a study organized by researchers at Oregon State University. Nine years later, they have crunched their data and have good news to report. They say that the test areas had more biodiversity and an increased level of forest resilience. James Johnston is one of the authors of the study. He is an assistant professor at OSU’s College of Forestry and he joins us now. Welcome to the show.

James Johnston: Thanks so much for having me, Dave. It’s great to be here.

Miller: It’s great to have you on. So you set out to see if you could restore forest resilience. What is forest resilience?

Johnston: Forest resilience is the ability of forests to absorb disturbances which are inevitable in these dry forests, disturbances like insect attack and wildfire and drought, and rebound to their former condition. In particular, we want to see old growth trees survive disturbance and we want to see understory vegetation that is reflective of and supportive of native flora and fauna.

Miller: What are some of the many factors that have diminished forest resilience over 100 years?

Johnston: Well, first, let me tell you, this study was conducted on the Malheur National Forest. That’s about a six-hour drive east and a little south of Portland. That forest is 1.7 million acres. That’s more than five times the size of Multnomah County. It’s a beautiful forest of Ponderosa pine and other dry forest species like Western large Rocky Mountain Douglas fir and Juniper. People have been managing the forest for thousands of years, but for most of the last 130 years or so, people have been making the wrong forest management choices. We logged many of the most fire resistant old growth pines and we suppressed the frequent surface fire that removes young trees and creates the space for old growth to thrive. And so what we’re looking to do with selective thinning is to create the space for those old growth trees to thrive and to create enough resources so that there is increased native biodiversity in the understory.

Miller: Your study focused on the results of mechanical thinning. What does that actually mean?

Johnston: The forest service works closely with collaborative stakeholder groups like the Blue Mountains Forest Partners, who’ve been on your show before, and the Harney County Restoration Collaborative, to identify areas that are in need of treatment. They select treatment units within that planning area, and mechanical equipment gets out there in the woods and selectively removes some but not all of the younger trees, while keeping all of the old growth Ponderosa pine, Western large Douglas Fir.

Miller: Can you give us a sense for how many trees, or the size of them, or the percentage of them that you have to take out in an average part of one of these units? I mean, I guess I’m just wondering what thinning means in terms of the before and after.

Johnston: Sure. Well, you can take a look at the paper we published in Forest Ecology and Management and don’t worry, you don’t need to actually read it. There are photographs, you can skim through it, and we include quite a few of before and after photos so folks can get a sense of what the forest looked like before and after thinning. Now I’m gonna throw some forestry jargon at you - many of these stands had in excess of 200 square feet of basal area per acre before thinning. Basal area is essentially a measurement that’s loosely correlated with total stand biomass. And many of those stands were thinned between 50 and 75 square feet of basal area almost entirely by removing the youngest trees in the stand. The focus is to get reductions in total stand biomass in order to protect the old trees.

Miller: I mean, something like removing three-quarters. Why focus on the youngest ones?

Johnston: Because those are the trees that have grown up since we made the mistake of excluding frequent low-severity surface fire from these systems. In the distant past, these systems were characterized by pretty open stands of old growth, widely scattered individuals and clumps of old growth trees. When we exclude fire, it creates... What we get is a bunch of younger trees that grow up because they’re not killed by that frequent surface fire. So what we’re trying to do with these restoration activities is first remove the young trees with mechanical thinning and then reintroduce wildfire or prescribed fire to keep those younger trees out of the stands and allow those old growth trees to thrive.

Miller: So let’s zoom forward to the last couple of years after this thinning happened and you could see the results. There were some technical forest ecology terms in your paper that I didn’t understand, things like non-structural carbohydrates and forbs and graminoids. But if you walked me around these test plots, what would you be able to show me, show our listeners, as lay people, in terms of signs of forest health, visible signs of forest resilience?

Johnston: Well, trees, just like people, have a number of physiological mechanisms that make them resistant to disturbance and disease, and what my team did, essentially -not to get too technical- but we poked some holes in trees and extracted some material from those trees and took that material back to our lab and analyzed it. In particular, we’re looking to see how much resin trees produce and the degree to which they’re able to mobilize non-structural carbohydrates, which are just simple sugars that are usually at some point mobilized into wood tissue. And we found that the trees that were leftover after thinning were better at mobilizing resources. They had increased radial growth, they had increased leaf area, all of which are strongly correlated with the ability to withstand fire, insect and drought disturbance. So these trees are better set up to be able to survive for another 100, 200, or 300 years. Whereas before the thinning, they were at very high risk of being killed by fire and insects.

Miller: Is this because they’re getting more of the limited moisture that’s not being sucked up by their younger competitors?

Johnston: That’s exactly right. It’s almost like you read the paper. Yeah, water is the limiting factor for tree growth in that dry part of Oregon. And the biggest effect of thinning is that it makes more water available to the old growth trees, and so they’re better able to mobilize resources and devote those resources to defense against insects and fire damage.

Miller: I want to turn to the biodiversity piece now. What exactly did you find in the test areas compared to the control areas?

Johnston: Well, we measured changes in understory vegetation; that’s flowers, grasses - forb is another term for flower, by the way - and shrubs. We measured change before thinning and after thinning, and in that comparison, we found that there was a strong effect of thinning in increasing native plant diversity because there’s more water available to plants, and also because there’s more sunlight available to plants, particularly when we’re talking about forbs. And a forb, again, is a flower. These are light loving plants and they do a lot better when they have more access to sunlight, which is what they get when you remove some of those younger trees.

Miller: What about protected species, ones on the endangered species list, or listed in some other way?

Johnston: There’s a very strong relationship between habitat and endangered species. And we expect that when we maintain and enhance native plant diversity, we’re also maintaining and enhancing habitat for threatened and endangered species. It’s a separate study that we’re working on now, and we haven’t published yet, but one of the types of critters that we’re really interested in is pollinators, bees. And we think that we see an increase in bee populations as a result of this thinning, because there’s more flowers available to them.

There are endangered pollinators like the Western bumblebee, and we’re hoping that this thinning creates better habitat for those critically endangered insects. I know that doesn’t sound as sexy as a grizzly bear or a gray wolf,  but I hope your listeners will understand that we’d be really screwed without insects. And it’s really exciting to see this response in native floral diversity from the thin.

Miller: Have there been naturally occurring fires in the areas that we’re talking about in recent years to show us a true kind of natural experiment? Or do you have to rely on the markers of resilience that you described earlier?

Johnston: In a companion study, we modeled fire behavior and found that there were significant reductions in most metrics of fire behavior as a result of thinning. These stands have not yet burned, but they will burn, and we’ll be out there collecting more data to evaluate the effects of the fire and the thinning put together. We expect that those thin stands are gonna be much better set up to be resilient to future wildfire.

Miller: A federal judge recently determined that the US Forest Service broke a number of federal laws when it lifted a ban on harvesting trees more than 21 inches in diameter in six national forests across Eastern Oregon and Southeast Washington, with the stated goal of doing what you set out to study, of improving the resiliency of forests. What went through your mind when this news broke recently?

Johnston: Well, I read the judge’s decision. The judge ruled that the Forest Service had made a number of procedural errors. The judge’s ruling says that the Forest Service did not cross their T’s or dot their I’s properly with respect to the process by which the Forest Service consults with regulatory agencies.

Miller: Things like public comment periods, or a full environmental impact statement.

Johnston: Correct. The judge ruled that the Forest Service had provided the wrong type of environmental documents and that they’d failed to provide the right type of opportunities for public objections. But the judge’s ruling, I think, also made it clear that the Forest Service was following the science when it comes to changes to forest over time and the need for restoration. The study my team just completed adds to a large body of evidence that selective thinning works to restore forests. It’s unfortunate that the Forest Service hasn’t gotten its procedures down right to make needed changes to policy.

But we think that they’re on the right track with respect to the science, and hopefully they’ll be better able to utilize science in the future.

Miller: Are you saying that you think studies like yours could be used as part of the federal regulatory process, as part of an environmental impact statement, to show that these kinds of thinning plans can have the intended environmental benefits? You’re hoping that studies like yours will actually be used to make these things happen.

Johnston: One of the unique things about this study is that it’s very much driven by a collaborative stakeholder process. For more than 10 years, collaborative stakeholder groups in Grant and Harney counties like the Blue Mountains Forest Partners and the Harney County Restoration Collaborative have been working closely with the Malheur National Forest and with Oregon State University to implement accelerated restoration actions across the forest, and to monitor the effectiveness of those treatments. And with the benefit of 10 years worth of data collection, we’ve been able to conclude that those treatments are working.

So it’s some good news from Eastern Oregon for us for a change. And we anticipate that this study and past studies and studies that we’re working on as we speak will continue to be used in environmental planning and will continue to help build consensus among diverse stakeholders for how we move on with the necessary task, forest restoration.

Miller: I’m curious about these communities, economic health, and jobs. This is actually an area where we recently spent a whole week, and these issues, all the ones that we’re talking about, were really big issues when we were there, obviously. Is the amount of thinning or logging that was done for your test plots, would it be commercially viable? Would it even bring in enough money to pay for itself?

Johnston: Accelerated restoration funded through the Collaborative Forest Landscape Restoration Program created by Congress has been huge for local communities like John Day, Burns, Prairie City, Mount Vernon, Seneca. It has created more jobs. Many of these mechanical thinning operations do generate commercially viable wood fiber that’s processed locally and made into high value wood products, at the mill and John Day for instance. And so there is a big economic impact to these types of thinning activities in communities that have some of the highest unemployment in Oregon.

So, yeah, that’s critically important. And the economy is also important for ecosystems because we need that mill capacity and that workforce capacity in order to remove those young trees to protect the old growth trees. So the ecosystems and the economies are very intertwined out there in Eastern Oregon.

Miller: I wanna turn to this question of scale. How much land broadly in Central and Eastern Oregon is similar enough to the test plots that you studied to make you think that there would be similar results?

Johnston: There’s probably at least 15 million and perhaps as much as 20 million acres of Eastern Oregon that are similar enough to the areas where we conducted this research that I think we’d be able to apply the results of those studies to those other areas. And 20 million acres sounds like a lot, and it is. Oregon is only 60 million acres. So a pretty large percentage of the state could potentially benefit from these types of restoration activities. And it always seems to be bad news from Oregon Forest during the summer, with drought and out of control wildfires. I’m glad to be able to give some good news for Oregon forests and hopefully there’ll be more good news for an increasing acreage of eastern Oregon for us in the years to come.

Miller: Correct me if I’m wrong, but I feel like we’ve heard some of the basics of the results that you’ve been talking about, that thinning is necessary and thinning can work after more than a century of fire suppression and post logging monoculture, I feel like we’ve heard that many times now. What more do we need to learn before this can be applied widely?

Johnston: Well, there’s always new and interesting things to learn when you get out in the forest and collect data. But I think you’re right that we have more than enough information to be able to proceed with landscape-scale restoration. And that’s one of the things that’s really exciting about working out on the Malheur National Forest is, it’s a 1.7 million acre forest. We’ve completed about 250,000 acres worth of thinning in the last 10 years. And we’ve gotten money from Congress to complete another 250,000 to 300,000 acres worth of thinning in the next 10 years. And so we’re making a significant dent in the restoration needs at landscape scales, which is pretty unique and unusual for these dry inland Pacific Northwest forests to have that sort of landscape-scale impact.

We’re hoping to continue to build social consensus and to work through the legal challenges and legal barriers to getting needed restoration work done, and I’m hoping that we’re on the right path.

Miller: James Johnston, thanks very much.

Johnston: Thanks again.

Miller: James Johnston is an assistant professor in the College of Forestry at Oregon State University. He joined us to talk about the new study, for which he was one of the authors, that found that thinning a forest in Eastern Oregon increased its resilience to fire and its biodiversity.

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