The following individual was interviewed for today’s show. Our thanks to:

Elizabeth Reinhardt
Research Forester
Fire Effects Project – FiSL
USDA Forest Serice
Missoula, MT

Links:

WWF – “Global Review of Forest Fires”:http://www.panda.org/forests4life/fires/report_sum2.cfm

Interview with Elizabeth Reinhardt:

ES:

ER: I’m Elizabeth Rheinhardt, and I’m a research forester with the Missoula Fire Sciences Lab, a Forest Service research station.

ES:

ER: In the Fire Lab, in general, we we study fire behavior and fire effects and fuels, because fire behavior and fire effects are dependent on fuels that the fire’s burning. And a lot of research over the years has focused on surface fires, fires that are moving through the forest floor, through the litter and twigs and grass. And many of the fuel models and behavior models have dealt with fires moving in surface fuels. But, a big problem to managers is whether or not fires leave the surface and enter the canopy of the stand. Because crown fire behavior is more severe and the fires move faster and have more dramatic effect and are harder to suppress. So other people have been working on models for looking at crown fire behavior and occurrence. But those models were dependent on some kind of description of canopy fuels, and that was really lacking in previous work. So what we wanted to do is actually find out by destructive sampling, we wanted to characterize the fuels in the forest canopies. So we looked at 1/10th acre plots in a variety of forest stands, and actually mapped every branch in these 1/10th acre plots and weighed them. And then looked at how much of that material was of what size. So some of the larger material isn’t really available to the fire. What proportion of the material was needles and fine twigs, which might be expected to burn in a crown fire. and then we’re correlating that information with indirect measures of canopy fuels based on stand descriptions for one thing, photography, and optical sensors.

ES:

ER: Well, surface fires are moving through the material on the forest floor, or not necessarily forest, but grasses, or shrubs, or whatever. And they can be dramatic and hard to suppress also. But when a fire gets up in the crowns of the trees, and it’s moving from tree to tree through the treetops, it’s much more influenced by wind because, you know, it’s up there where the wind can really push it. And it tends to burn with much greater intensity and disperse faster. Well, it usually results in 100% tree mortality, a lot of smoke production, and it’s not as easily suppressed by normal firefighting techniques. So the difference between a surface fire and a crown fire is very dramatic. And some people think that there’s more of a tendency to have crown fires now that fire suppression has resulted, over the past century, in thicker forest stands, stands with more little trees, and so more of a pathway for fires to get up to the crowns.

ES:

ER: Well, we’re actually in 1/10th acre plots, we mapped every tree in the 10th acre plot, and then we took those trees apart branch by branch. The smaller trees, we cut and lowered to the ground and tool off each branch. But the taller ones we climbed and cut the branches off one by one, measuring their height above the ground. And then, once the branch was cut, we weighed it. And a subset of the branches we sorted by size class. So, the crew would actually pluck off every needle of the branch. And then they would take calipers and measure those 0-3 mm branch width, clip it off, and weigh that. And then they would measure the 3-6 mm branch width and so on. So that they got the branches sorted into stuff that would probably burn and that that would probably not burn in a fire. So we have that branch-by-branch data in the whole plot, and that allows us to have a three-dimensional estimate of available canopy fuel and the bulk density of the canopy fuel. And how it’s varying both vertically and horizontally.

ES:

ER: Well, the larger branchwood doesn’t burn, a crown fire doesn’t burn for more than a few seconds at any given time. The larger branchwood isn’t usually burned. It’s mostly the foliage and the very finest branches that would be consumed by a fire. So we got total branch weight for every branch. For a subset of the branches, we we sorted out by size class, I mean we developed regression equations to estimate for the branches, but we didn’t sort how much of their weight was available for fuel as opposed to just bigger, chunkier branches that wouldn’t burn. A lot of people think that a branch with less than a quarter of an inch in diameter will burn in a crown fire, but not much that’s bigger than that.

ES:

ER: Well, there’s two aspects with a canopy fuel bed that are pertinent. And one is, how dense it is, how much fuel is available to the fire. And that’s the canopy bulk density. So how much – trees per acre – is relevant to thinking about how much biomass is up there, but a similar aspect that’s really relevant is how far that is off the ground. So how likely is it that surface fire can ignite the canopy fuels. So in other words you have a really dense canopy, but if it’s separated by a long distance from the surface fuels, because it’s high off the ground, it might not be very available to crown fires. So vertical continuity, and then also horizontal continuity are the two things we’re looking at, amount of fuel and where it’s located.

ES:

ER: We had a crew of five people. One or two people would be up in the trees cutting, climbing the trees and cutting off each branch, and the crew on the ground would be retrieving the branches and weighing them. And then – usually they would do that in the morning – in the afternoon they would sit and pull off the needles and sort the material. They like the climbing the best, they don’t really like the sorting, it’s pretty tedious.

ES:

ER: We have a plot just outside of Missoula and near ###, Idaho, one near Flagstaff, Arizona, one near Sacramento, and one over in Central Montana.

ES:

ER: Well, we try to look for sites that would be considered crown fire prone. We also tried to look for a range of
sites, because this is a real first effort, so the sample size isn’t big, but we wanted to try and get some typical stands. As we took the trees out, we took them out in four levels too and repeated our optical measures for each tim. First we took all our optical with the untreated stand, as dense as it could be. Then we removed a quarter of the trees, sampling them as we went, and repeated all our optical measures. We tried to get a representation that way so that we could get treated, or thin stands as opposed to untwined stands, by starting with the densest stand we could find. Progressively removing trees is kind of like, we were looking at a range of stand conditions within that same plot.

ES:

ER: A lot of people are wondering what they can do to make forests a little less vulnerable to crown fire, and especially forests near communities or where people are living out in the woods. Homeowners want to know: if they thinned the stands around where they live, will they be protecting themselves somewhat from crown fires? So people are wanting to map fuels and wanting to develop fuel treatment plans. But there’s this gap. Someone might want to map canopy fuels so that they can model potential fire behavior, but nobody had ever measured canopy fuels. So there was really this missing link in there. That’s why we got into it. There’s a big question now about whether thinning stands is an effective way of protecting them from crown fire and from severe fire, I think, the verdict is still out to some extant. But the first step is actually just quantifying what’s out there.

ES:

ER: Some people think, and in some forests in particular, that fire suppression over the last century has really changed the structure of the stands and made them denser and more clogged with trees. And they’re supporting a lot more trees than they used to, before fire suppression when they used to burn periodically in a cycle from every 6 to 10 to 20 years. And all of a sudden they haven’t been burned for 50 or 100 years. and lots of little trees have grown up and created theses dense thickets, they’re more vulnerable to crown fire.

ES:

ER: Well, the crown fuel is the conifer needles and the finest branch width in the stand. so the big limbs don’t usually burn in the forest fire. But the needles, and maybe the branch width that’s less than a quarter of an inch in diameter is consumed in a crown fire.

ES:

ER: So we’re just looking at the needles and fine branch width on standing trees, basically. Surface fuels are usually fuels that are considered to be within 6 feet of the ground. So the very smallest trees and shrubs are usually considered part of the surface fuel complex. And sometimes people talk about ladder fuels, which are intermediate sized trees that might serve as ladders to carry a surface fire up into the crown.

ES: What do scientists do with this information?

ER: Well, first thing we’ll do is – we haven’t really done a lot of the data reduction yet but we’ll end up with a three dimensional grid, basically, showing available fuel horizontally, vertically, within this 1/10 acre plot. Then we’ll try and correlate our indirect measures of crown fuel – this would be to develop tools that managers can use. this destructive sampling is very labor intensive. It could never be done on a district by someone who just wanted to know what was out there could never do that because it would take months to do a plot. So we’re trying to correlate out observed data – indirect measures which we get from stand tables, aerial photography, and leaf varying index optical sensors – and hopefully we’ll get correlation that we can use to develop a methodology that will tell people: here’s a way to go sample your canopy fuels without doing destructive sampling, based on a combination of stand inventory data and some kind of optical sensor data.

ES: How do you measure the success of the program?

ER: I guess in the long run I’ll measure it by the tightness of the correlation that we obtain between out direct and indirectly measured data. And hopefully we’ll get some pretty tight statistical relationships. And another thing is that it was a real relief to get through two seasons of climbing trees without having injuries, so that was in a personal way a measure of success. I was kind of nervous about having people high up in trees with saws, but they did fine and nobody got hurt. That was a measure of success for me.

ES:

ER: One thing that was dangerous was these falling branches, some of them were quite large, and so the people on the ground had to be careful about stuff falling out of the sky on their heads. And then the other thing that’s kind of dangerous is being up in the tree and up in the tree with a saw. When they got up to about a four inch diameter, they would top the tree, so that’s kind of a tricky part because then the whole remaining crown of the tree – you know they just cut off the top of the tree, it flings over and falls to the ground, and then they’re just up there on a tall pole with no limbs on it, which after the top is cut off, the remaining tree sways back and forth, so that’s kind of spooky.

ES: What motivates you to take these kind of risks and do this?

ER: It’s not really in the line of what I’ve done before, I just wanted to do something that generated some hard numbers, that we could actually observe these values – canopy bulk densities – which people are always talking about but actually never really measured. So that was a motivation to me, that we could actually get some data that we knew for sure – at least on those 1/10 acre plots – what there was out there.

ES:

ER: One thing is that there’s so many forest types that even within one forest type, there’s so many stand structures. This study was just barely scratching the surface in terms of getting a lot of descriptive information. But because it was a new methodology, it was a pilot study as opposed to an all inclusive study. So after we’re done writing down all our data, in some ways we’ll just have these five data points – one on Flaggstaff, one in Missoula, one in Idaho, but we’ll hopefully develop the methodology that people can use to develop some additional data points with less effort.

ES:

ER: Well, there’s several different ways that you can treat fuels to treat fuels to make them less vulnerable to crown fire. One would be just to treat the surface fuel, because if surface fuels were reduced and you didn’t have much of a fire really moving through there, then it wouldn’t get up in the crowns. If surface fire intensity was always really low, it wouldn’t matter if the crowns were dense. You just would be unlikely that you would have a lot of crown fire. and in that way you would reduce what we call the ladder fuels, sort of the intermediate sized trees that the fire climbs to get up in the canopy. And then the third is to reduce the canopy bulk density, which would mean just a wider spacing of the overstory trees. Not everyone agrees on how much thinning has the potential to reduce crown fire. Some people think that it opens stands up and makes them drier and makes conditions windier near the forest floor which would result in greater surface fire intensity, so you actually might have more crown fire. but I don’t think there’s a simple answer. It just sort of depends on the relative contribution of all those different factors, the surface fuels, the ladder fuels, the canopy fuels, the solar radiation, and the wind speed. So, there might ne situations where thinning might be an effective tool.