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Science and Innovations

Study: Forest Restoration Shows Benefits Decades After Initial Treatment

Melissa Sevigny

A new study from Northern Arizona University looks at the long-term effects of restoring a forest with mechanical thinning and prescribed burns. The news is good: treated forests are healthier and more resistant to catastrophic wildfires, and those benefits seem to last. But climate change adds a wild card. KNAU’s Melissa Sevigny spoke with forest ecologist Mike Stoddard about the findings.

Tell me what was the question you wanted to answer going into this study.

The main question I really wanted to answer is just how long these treatments had a shelf life for. We’ve been doing this restoration projects or treatments around Flagstaff and throughout the West for several decades now. One of the questions when it comes to foresters is how long these treatments last before we have to come back in there and start the process all over again, or do some sort of maintenance. We’re really lucky in the fact that we had 20 years of data so we could look at those sorts of questions.

Tell me about some of your results, what did you discover was working in the treated areas?

We saw better growth in these forests. We saw less mortality.…. And what we see in these particular treatments is the risk of canopy crown fire is reduced. Because you have less trees, you have less continuous ground cover, so you don’t have that forest that is continuous and allowing fire to rip across the canopy.

How long did these positive effects last?

That was the big surprise. That was what really came out of this study. These sites seem to have a twenty-year shelf life. As of right now, we’re still seeing beneficial effects of these treatments. Who knows how long, further they could go? …. It gives managers opportunities to move on.

They don’t have to go back and thin every five years?

Sure, exactly. These particular treatments are pretty aggressive… and then we’ve come up into some of these sites with fire. Well, all the sites we come in with the fire afterward to clean up some of the understory and get rid of fuel accumulation. But only a few sites have had recurring maintenance of fire.

All good news so far, how does climate change change the story?

Regardless of treated or nontreated, we see concerning losses of ponderosa pine basal area in the future. A lot of these forests look like they’re going toward less trees or less basal areas.

Really quickly, define basal area for me.

Basal area is the amount of area in a given area that trees encompass. If you have an acre, how much of that area is encompassed by trees…. The good news is the treated areas seem to retain some of that basal areas, compared to untreated areas. That’s the positive spin. The negative spin is climate change is really hampering these forests….. A lot of things are happening right in our face, right now. North of the Peaks, some of the big juniper die-off. Seeing some of the ponderosa pine and the browning, or the dieback.  I’m hopeful, in these gloom-and-doom times, it would be nice to have something to have some sort of faith in. Doing treatments on the ground, doing them where we don’t have to come back every five years, it’s really important because there’s so much out there that land managers have to deal with. Knowing that there is some long-term benefits is really important.

Mike Stoddard, thank you so much for speaking with me.

Thank you very much.


Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.
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