To Burn or Not to Burn? A Framework to Answer the Question

[Damon Runberg] Hello and welcome to the Oregon Science Podcast. I am Damon Runberg.

Today we’ll hear an interview recorded last month with USGS Forest and Rangeland Ecosystem Science Center research ecologist Dave Pyke.

I sat down with Dave to speak about his current research on the use of fire as a restoration tool. A prescribed burn is one strategy for controlling the spread of invasive and non-native species. Dave recently developed a method to help land managers predict results when they use fire to control or enhance certain plants.

[Damon Runberg] Dave, thanks for joining us today.

[Dave Pyke] You’re welcome.

[Damon Runberg] When land managers use prescribed burns, what are they trying to control?

[Dave Pyke] Sometimes they use it to control weeds, but other times they use it to benefit the plants that are remaining after fires. So, it can go both ways.

[Damon Runberg] One issue that comes to mind when I think of prescribed fires is a lack of predictable behavior. What makes fire so unpredictable when using it as a management tool?

[Dave Pyke] Fire is dependent upon the kinds of conditions and the types of fuels present that will burn. The best we can do is to make an estimate of how well that fire is going to burn. When we start a prescribed burn, we are trying to keep it under control. However, control is a relative term, as weather oftentimes regulates how well that fire is going to burn, as well as the landscape position. It’s much easier to burn up a hill than down a hill and, if the wind is blowing, the fire burns faster. The problem is that when a fire starts to burn it also creates some of its own weather.

[Damon Runberg] I have read the term “fire regime” in your paper and other works that I have seen. What exactly is a fire regime?

[Dave Pyke] Fire regime takes into consideration both the combination of the factors that are created by weather, climate, and landscape positions, in combination with the types of fuels in that area. These fuels include what has grown in that area, what plants have died, what remains - essentially all the plant material that is there. What is the plant is made up of or what kind of chemistry does it have? Some plants have oils in them that burn better, which means that the chemistry of the plant can actually affect the fire. Fire regimes also take into consideration the length of time you have between burns. You can think of every ecosystem as probably having a component of fire as a natural disturbance.

[Damon Runberg] How has the history of fire suppression that we have seen in the last one hundred years affected these fire regimes?

[Dave Pyke] We have manipulated fire regimes through changes in fire suppression. In some areas we have suppressed fires more often than they would have been in the past or caused a change in the frequency of fires. A good example of this would be in many of the areas that are shrub-grassland systems in the Great Basin. In these systems, we have tried to suppress many of the fires at higher elevations, because they are very close to where the forests are and oftentimes close to where people live. By suppressing these fires, we have at the same time restricted the frequency of fire, which has caused there to be a longer interval between fires. This has allowed the plants that normally would be susceptible to fires to move into that area. For example, juniper and piñon trees across the western United States are susceptible to fire. However, if we control fire, then they will expand into and ultimately begin to dominate many of these shrub grasslands.

[Damon Runberg] Are there any circumstances where we see that fire has actually been increased in certain fire regimes?

[Dave Pyke] We have many ecosystems in the western United States where we now have invading plants from other parts of the world. They were never seen in these plant communities before and are now moving in and changing fire regimes. These invasive species increase the amount of fuel and make fires more frequent in many communities in the western United States. In the Sonoran Desert around Arizona, we have seen the invasion of buffelgrass, which was originally planted as a forage crop for livestock. It has now escaped and is moving through many areas in the Sonoran Desert. This area historically had fire maybe once every couple of hundred years, and now in areas where buffelgrass has invaded, we are seeing fires occurring less than twenty years apart. We have several different examples where we can get reductions in the length of time between fires, as well as an increase in the time between fires.

[Damon Runberg] Why would someone use a prescribed burn instead of other management strategies, such as herbicides or simply pulling the plants out?

[Dave Pyke] A prescribed burn is going to do things that you would not be able to accomplish with these other techniques. An herbicide treatment may or may not be specific to a certain plant, and it may impact all of the plants within a system. Going through and trying to pull individual plants is backbreaking work and time-consuming. It can also be very difficult to do for many plants because their roots are deep, and it could be difficult for individuals to pull them out.

[Damon Runberg] It seems that there are only so many things that we can control when it comes to fire. What are some of those factors that we can control? Inversely, what are some of those factors that we cannot control?

[Dave Pyke] What you are getting at are some of the drivers associated with fire regimes, and it’s a very good question. We can control factors that are relative to the vegetation that is on the landscape because that is the fuel that is used in the fire. We can actually manipulate these fuels by mowing vegetation before burning it. Uncontrollable factors include things like weather or topographic position (position on the landscape). A south-facing slope that gets the sunshine every day and is very steep is going to be an area where the vegetation is going to dry quickly. If a fire starts at the bottom of the hill, then the fire will very quickly make it to the top of the hill.

[Damon Runberg] When do land mangers know when it is appropriate to use a prescribed burn?

[Dave Pyke] They actually have a very long and detailed process that they go through when making that type of decision. First, they are going to take into consideration how close they are to where humans are living. Fire managers will try to make sure that they are not going to be in an area that may run the risk of the fire escaping and burning buildings or causing problems for human habitation. The next thing that they would consider is the type of vegetation that they have and what the objective is for that fire. If their objective is to try and control a plant that is in that area or reduce the impact of a plant, then they want to make sure to use the type of fire that would be most appropriate to control that specific plant. You can have fires that burn at or near the soil surface, or you can have fires that might burn in the canopy of trees and not even touch the soil surface. If you are trying to control the plants that are on the soil surface while allowing the trees to survive, you want to make sure that the fire does not get into the canopy of the trees.

[Damon Runberg] I understand that you have been developing a decision framework for using fire to either control or enhance plants. Can you give us a brief description of this framework?

[Dave Pyke] The framework itself is dependent on how a plant grows, and how that plant grows will determine its susceptibility to fire. The framework also pays attention to the growing points of the plant. If you think about a grass, it grows from the ground up. Trees and shrubs grow from the branches, and every year they put on more growth from those branches to grow taller. The types of fires that can be used to control each of these plant types might be different.

[Damon Runberg] It seems like your framework really looks at how these plants are going to respond individually.

[Dave Pyke] Individually, in terms of how the individual plant species would respond relative to one another. A plant community is made up of a number of different species; some of those plants are going to be more or less susceptible to fire.

[Damon Runberg] Knowing how these plants are going to respond to fire, how do you use that as a fire manager for making decisions?

[Dave Pyke] You have to know what the objective is. Are you trying to control a plant? Knowing something about that life form and knowing something about how those plants grow tell you what type of fire you need. Can you get by with a fairly cool fire and control the plants that you want to control? Or, are you going to need a very hot fire in order to control that plant? If both groups of plants are going to be killed, then maybe fire is not the appropriate tool to be used, and you should be using some other tool to try and control that group of plants. However, if you can use fire, then you should be able to get control of the one group that you want to control and potentially enhance the other group that would be remaining after the fire.

[Damon Runberg] Thank you very much for joining us today, Dave.

[Dave Pyke] It’s been my pleasure, thank you.

[Damon Runberg] That’s all the time we have for today’s episode. Make sure to check out our transcripts for links to more information on the research going on at USGS FRESC. For those who subscribe through iTunes, you can access the transcripts at our website: or.usgs.gov/podcasts. If you have any questions or comments about the USGS Oregon Science Podcast, please email us at oregonpodcast@usgs.gov. As always, thank you all for listening. If you want to hear more about other research the USGS is doing around the country, please check out the other USGS podcasts at usgs.gov/podcasts.

Until next time, I’m Damon Runberg.

This podcast is a product of the U.S. Geological Survey, Department of the Interior.