After wildfires burn through forests, there are often efforts to re-plant trees in those affected areas. But, new research offers some guidance on how to do that, as well as when those efforts should, and should not, take place.
Kyle Rodman, a research scientist at NAU’s Ecological Restoration Institute and lead author on the paper detailing this, joined The Show to talk about what the team of scientists found, starting with the size of this study.
It looked at more than 300 fires in the western US, excluding the west coast, over the course of a few decades, and if Rodman felt it was right that this kind of research hasn’t really been done at this scale before.
Full conversation
KYLE RODMAN: Right? Exactly. Yeah. So there have been a handful of studies that have looked at essentially how tree planting after fire can affect what's going on on the ground, the outcomes of those activities, right? And many of those studies in the past have been focused on maybe one to five different wildfires that have happened in a particular state or a particular part of the country, right? But these activities are done all over the place, right?
We've, we've identified hundreds of individual wildfires all across the western US that plantings have been done on federal lands in the United States. And if we don't have a sense of how well those are working across a large area, we don't really know how to know whether the money that we're spending on these things is actually worthwhile, right? That's a key piece, because it's an expensive thing to do, to put trees in the ground and get them out there on the landscape.
MARK BRODIE: Aren't the different kinds of forests similar enough that what you find, you know, for example, in northern Arizona might be applicable to, you know, somewhere in Montana, for example?
RODMAN: Yeah, that's a great question. You know, many, many of the forests in the western US have similar kinds of dynamics, but there are different species that grow in different places, different kinds of trees that grow in different places. There are also different climatic conditions in different areas.
And these are all things that we actually looked at in the study, how those factors might actually affect the outcomes of planting, right? Because people are planting all sorts of different tree species in the western US, and they're planting those in different areas that may or may not be suitable climate for the kinds of trees that are being planted in those areas, right?
BRODIE: So what did you find then, in terms of what strategies tend to work best after a wildfire, to get trees back into those places?
RODMAN: Yeah, so in a lot of the places that we were looking at, plantings are typically done in the spring or fall, sometimes in the early summer, right? And there are certain things that people that do these activities have control over, they may not have control over the weather, which is important, if you're a gardener or you do you know this kind of work, like forestry work, weather plays a big role in the outcomes of these things.
So if you're a forest service person, you go out and do a tree planting activity, and you get a couple dry years afterwards, it's likely that you're gonna see a lot of mortality. That's not something that many people have control over. What we do have control over is the kinds of places that we can plant trees. We have control over the seasons that we plant trees, and there's a certain amount of control that we have over like the kinds of trees that we're using, right?
There are different ways of growing trees in the nursery. There are different species that you can plant in different areas. So some of the things that we found in this study, if you're planting in places that are warm and dry, it often makes sense to try to plant in the fall season, right? So after the hot, dry summer period, so those trees go on the ground, they have a few months before things get hot and dry again, and they can sort of get their feet under them, in a sense, right?
But if you're planting in a cool, wet area, like many places in Montana or Idaho, for example, planting in the spring can work pretty well, and traditionally, that's what's been done in a lot of those places. So it's kind of nice to see that the knowledge that people have that goes into planting these things and has for many decades, kind of lines up with what we are now seeing. Works quite well.
There's pretty good evidence that the sites that you select for planting can have a big effect on the outcome. So if you, if you plant on, let's say, a hot, dry, south facing slope at a low elevation site, probably you're going to have more of the planted trees die, and the ones that survive may not grow as fast as a planting that happens on like, a high elevation, wetter place, right? So there's a few things that managers have kind of within their toolbox that they can control that do actually affect the outcomes of plantings.
BRODIE: Yeah, I was going to ask if there might be some places where wildfire goes through that just aren't really suitable to replant trees. Or it sounds like in some cases, there might be?
RODMAN: Yeah, absolutely. You know, this is something that I think many people that live in and around forests want to see places return to forest if they were there before the fire. But. Even kind of the combination of some of those places being pretty harsh for trees in general, and things getting hotter and drier.
Now, there are some places where almost no matter what we do, we're not going to be able to get trees to grow back easily. So if we're thinking about how to maximize our investment and try to get the best bang for our buck, in a sense, avoiding some of those places might actually make a lot of sense. Right? Where you're going to be essentially throwing money in a hole to try to get forests to grow back.
BRODIE: I'm curious what you found about the timeline of some of these replanting efforts, in terms of when, after a fire, it might be a good idea to go. And it seems like there might be some debate about whether you sort of wait and see what happens, you know, what the biome does on its own, versus having people come in and move it along a little bit?
RODMAN: Yeah, you know, that's, that's a great question. And I think one of the things that we often say as foresters or as ecologists is it depends. So in some places, for example, in the West Coast, there are a lot of shrubs or re sprouting trees, like Aspen is a good example of this, right?
But there, there are these trees that have this adaptation to grow back immediately after fire from roots that survive the fire. Many broad leaf deciduous trees are capable of doing that, and there are many deciduous trees and shrubs on the west coast that grow back immediately after fire. So if you're working in an ecosystem like that, you kind of have to get in there early if you want to plant trees after a fire, right, and get things like conifers established, because the site will get taken over by other species that you may or may not want in that area.
But in other places, like, you know, certain areas around Arizona and other places in the southwest, where things grow back pretty slowly, we may have a little more time, right? And that's, that's kind of a nice thing, because if we have a few years to wait and see what happens, we're going to see how the natural processes play out, and maybe some forests do recover on their own, right? So those are places we can avoid with planting, right? If planting is really intended to accelerate their recovery of forests, but they're coming back fine on their own. There's no need to do it.
BRODIE: Is that more of an ecological decision or a financial decision, or maybe both?
RODMAN: Yeah, I would say it's a combination. You know, that's one of the interesting things about this issue, is that it kind of brings in a bit of ecological decision making, but also some financial considerations, right? Like, sort of the overall cost of different things. It's much, much cheaper to let a forest recover on its own than to go in with a crew and do planting, right?
And there's also various stages of investment throughout that process, the reforestation pipeline, people call it, where the seed is collected, the seed is then brought to a nursery and stored. It's grown in a nursery, and then those seedlings are transported to a site and planted in the ground. So there are all these different stages that lead to a pretty high cost, right? So if we're able to avoid that cost in any way, that's usually the preferred option.
