for 426 fire management and ecology - university of idaho

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FOR 426 Fire Management and Ecology

Fire as a physical and ecological process

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This is hands-on learningThis is hands-on learning

• You need matches (wooden ones are good) or a candle and a place you can burn them safely.

• Light them. I want you to think about the processes going on:• Physically: heat is being transferred. Where and

how and why? • Chemically: what is going on, why and how?• Ecologically what are the implications of heat for

plants? Soils?

We will begin with a simple experiment. I would like each of you to get matches and a candle, and make sure you are in a safe place to light it. Now go ahead and light one of the matches or the candle. As it burns think about what processes are going on and how these processes can help us understand the ecological implications for plants, animals and soils.

The two main processes that you should have noticed were the physical process of heat transfer and the chemical combustion process. We will cover each of these in this lecture as well as some of the ecological implications of these processes.

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Fire as a physical processFire as a physical process

• Heat and temperature• Intensity

• Heat transfer:• Convection• Radiation • Conduction

Lets begin by discussing the physical process of heat transfer. To begin lets define what heat is. Heat is a form of energy. It is often measured as temperature. As the temperature or heat of a substance increases, the molecular motion also increases. Molecular motion is known as kinetic energy. In fire ecology and management knowing the temperature is often not very valuable to us, instead we are typically concerned with the intensity or heat flux. The fire intensity is the amount of heat or energy released per unit of fuel consumed per unit of area. Heat transfer is the process by which energy or heat is moved from one source to another source. Understanding the heat transfer principles is critical to understanding the ability of a fire to start and spread. There are three modes of heat transfer: convection, radiation and conduction.

Convective heating is the transfer of heat by the movement of a gas or liquid. In general, currents of hot air move vertically unless they are affected by wind or slope. Convective heating is an important for preheating of high fuel layers, such as the forest canopy, in wildland fires.

Radiation is a form of energy that exists as electromagnetic waves which travel at the speed of light. Radiation typically provide most of the energy to preheat fuels ahead of a fire front. Radiation and convective heating can only transfer heat to the fuel surface. Once heat has reached the fuel surface it is transferred by conductive heating.

Conductive heating is the transfer of heat by molecular activity. Essentially, conductive heating allows heat to transfer from one part of a burning log to another part or between two logs in contact with each other

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Examples of heat transfer in wildland fireExamples of heat transfer in wildland fire

• Heating the fuel• Radiation• Convection• Conduction

• Cooling the fuel• Radiation• Convection• Conduction

As an example of the importance of heat transfer principles lets consider a fundamental question we often talk about in wildland fires, predicting the rate of spread of a surface fire. We will talk in more detail about fire modeling later, but for now let’s just consider fire spread to be a series of individual ignitions, where the heat from one fuel particle (the heat source) raises the temperature of another piece of fuel (the heat sink) until it ignites. Ok so far? Sounds simple, right?

Remember that during heat transfer, any one or all of the following physical processes contribute heating the next piece of fuel to the ignition temperature:

1) Radiative heating from the flame to the fuel2) Radiative heating from the pyrolysis of fuel and associated flame to the fuel (below the fuel bed surface)3) Conduction of heat through the fuel bed4) Convective heating of the unburned fuel by hot gases from the flame

The following process are acting at the same time to cool the fuel bed.

1) Convective cooling to the atmosphere2) Conductive cooling downward through and out of the fuel bed3) Radiation from the heated part of the fuel bed

As you can see the process of heating a fuel element to ignition temperature can be very complex when we think about all of the heat transfer mechanisms going on.

How do you think that wind and slope affect each part of the heat transfer?

Is the heat transfer process the same for a live plant as for a stick of wood?

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Fire as a chemical processFire as a chemical process

C6H12O6 + O2 6CO2 + 6H20 + energy

Photosynthesis

Decomposition

combustion

Combustion is a chemical process that releases the energy bound in the complex organic compounds in wood, grass or other vegetation (here symbolized by C6H12O6 – you’ll recognize that as the general chemical formula for carbohydrates).

Combustion is often called rapid decomposition. Both of these processes, decomposition and combustion, result in the breakdown of organic compounds into their component parts. Both are in some ways the opposite of photosynthesis.

Decomposition and combustion have other similarities as well. Can you think of some of the differences and similarities between these two processes?

1) Both release energy, and they take energy to get started. 2) Nutrients are released during both combustion and decomposition. These processes release the

nitrogen, Ca, Mg, K, and other nutrients that were incorporated into the organic compounds as plants grow – they are part of proteins, cell structure, etc.

3) Both are often incomplete. In spite of how the formula above is written, combustion and decomposition seldom break down organic matter down completely. Pieces get smaller and there are many partial combustion products (CO, NO, tars, resins, etc.)

4) Both make nutrients more available, at least temporarily.5) Combustion is usually much more rapid than decomposition. During combustion, some

compounds are volatilized or otherwise carried away in the wind and smoke. 6) Can you think of any other similarities and differences, or other ecological implications?

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Phases of combustionPhases of combustion

• 4 phases of combustion• Preignition• Ignition

• Lightning• People• Spontaneous

• Combustion• Flaming combustion• Smoldering or glowing combustion

• And extinction

The process of combustion has four distinct phases beginning with preignition of the fuel. Ignition leads to combustion followed by extinction.

The process begins with a a series of endothermic reactions and ends with an exothermic reaction. In other words, heat is absorbed and then released.

We will now explore each of the stages of combustion to better understand the process as a whole.

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• Preignition• Dehydration

• Water• Oils and waxes• Other compounds

• Pyrolysis• Combustible gases

The preignition phase of combustion is a series of endothermic reactions which raise the temperature of the fuel to the ignition point. As the fuels are heated they produce combustible gases. There are two processes which are at work during the preignition combustion phase: dehydration and pyrolysis. Dehydration acts first to drive off the water in the fuel particle and also causes the volatilization of waxes, oils and other compounds. As the temperature increases, pyrolysis takes place which drives off combustible gasses. Pyrolysis is the thermal breakdown of fuel. The compounds released during pyrolysis are later involved in the combustion phase.

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• Ignition phase• Fire spread and ignition

• Fire spread is a series of individual ignitions

• Sources of ignition• Lightning• People• Spontaneous combustion• Volcanic activity

Ignition is a transition between the preignition phase and the combustion phase. The process from pre ignition to combustion is important because a fire can be viewed as a series of ignitions where heat is supplied to the fuel from the first ignition, the surface is dehydrated and than pyrolysis begins. Once the fuel particle can support combustion the fire spreads.

The initial ignition source can be lightning, humans, spontaneous combustion or volcanic activity. Ignition from lightning is by far the most general and widespread cause of wildfire ignitions. Although lightning is the most common source of ignition in most areas in the western United States, human activity has historically played an important role. Anthropogenic fires were noted by European settlers for North and South America as well as Africa and Australia. Human-caused fires have been started accidentally and on purpose (the latter is usually known as arson). Ever since humans first learned how to control and use fires, humans have used fire as a tool to increase forage, change understory vegetation by favoring one species over another, to manage fuels and reduce fire hazard, as weapons during wartime, and in many cultural and ceremonial ways.

Pyne (1996) provides information about the relative importance of ignition sources for the United States. He reports that about 9% are caused by lightning, 19% from smoking, 18% from debris burning, 6% from campfires, 8% from machine use and 26% from incendiary fires. Incendiary fires are fires which are set willingly to burn vegetation not owned or controlled by them and without permission of the owner or his agent.

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• Combustion• Flaming combustion• Smoldering or glowing combustion

• Photo by Dale Wade USDA Forest Service

There are two types of combustion, flaming and smoldering (also known as glowing combustion). Each of these involves different processes, with very different appearances, rates of heat production, and effects on the surrounding environment.

A flame from a burning piece of fuel is considered flaming combustion. In smoldering or glowing combustion, no flames are present.

Smoldering combustion can have dramatic ecological effects.

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• Extinction• Termination of combustion

• Which of the following do you think has the lowest extinction point in terms of fuel moisture? And why?• Dead grass• Forest litter• Chaparral

Extinction is the opposite of ignition. It is a transition point from combustion to non-combustion. Extinction occurs when there is a limiting factor in the combustion process, such as the loss of oxygen or a high moisture content.

Another common way a fire may be extinguished is through a weather event such as a downpour. Latham and Rothermel (1993) developed probabilities to help predict the occurrence of such a weather event for the Pacific Northwest. Although this tool is not based on the physics of combustion it provides an indication of the kinds of conditions under which the probability for the extinction phase of combustion to occur is high.

To answer the question above we may think about the chemical properties of these types of fuel. However studies of the intrinsic fuel properties have failed to relate chemical properties to the sensitivity to moisture content. Pyne et al. (1996) report extinction points for dead grass (15 to 20% moisture content), forest litter (30% moisture content) and chaparral (100% moisture content). So we can see that chaparral can burn at much higher fuel moistures than either dead grass or forest litter. Why?

Define moisture of extinction. Why is it different for different types of fuel? Do you think it is something useful to know for the types of fuel you work with often?

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Fire BehaviorFire Behavior

• Fire behavior principles• Fire behavior triangle

• Fuel• Topography• Weather• And Fire

• Types of fires• Surface• Ground• Crown

The behavior of a fire is dependent upon the environment in which it is burning. The fire environment triangle was developed to include the major factors affecting fire behavior. Four variables are identified in the fire environment triangle, fuel, topography, weather and fire. These four factors all influence each other and are influenced by one another. Fire is placed in the middle of the triangle to symbolize the interaction of fire and the environment. In most cases fuels, weather and topography will determine the fire behavior, but in some cases fire can influence the environment and thus its own behavior.

Depending upon the interactions of these factors we will see different fire behavior. We can characterize fire behavior based upon many different factors but typically we use the type of fire as a basis.

There are three common types of fire behavior: surface fires, ground fires, and crown fires. Surface fires are fires which spread through fuels at or near the soil surface, such as grass and forest litter. Ground fires are those which spread in the subsurface organic fuels such as peat. Crown fires are those which spread in the canopies of the fuels. Crown fires have been further divided up into three types (dependent, independent, and active) by Rothermel (1977). The definitions are based on whether a fire burning through the canopy is dependent upon the surface fire, is spreading independently of the fire in the other fuels, or if the surface and crown fires are spreading simultaneously.

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Characteristics of wildland firesCharacteristics of wildland fires

• Fire Behavior• Fire intensity• Rate of spread• Flame characteristics

• Length• Height• Angle

• Fire effects• First order fire effects

• Mortality• Air quality

• Secondary fire effects• Plant response, erosion, habitat change, etc.

We can further describe wildland fires based on the characteristics of specific fire properties. Typically we use a combination of a few properties to describe a fire. For example we could report the rate of fire spread, the type of fire and the fireline intensity of an active fire to plan how we might attempt suppression. Or we could describe a previous fire using the type of fire, or we could use a combination of first order and second order fire effects to help plan rehabilitation efforts.

Fire behavior modeling can help us predict the outcome of a given fire event.

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Fire behavior modelingFire behavior modeling

• Andrews and Queen (2001) characterized fire modeling into 4 areas.• The fire environment• Fire characteristics• First order fire effects• Second order fire effects

A complete review of fire models is outside the scope of this course. Instead we will review how we classify fire models and specifically look at surface fire spread models. To begin with though, we need to think about how we classify the many fire models which have been developed. Andrews and Queen (2001) provided a basic framework for thinking about fire models. They suggest that all fire models are in one of four broad categories. Models of the fire environment are used to describe or predict information about fuels, weather, and terrain. These types of models are often used to get the required inputs for fire characteristic models. Fire characteristic models are models which apply to the actual fire itself. This group of models includes the traditional fire intensity, spread, and flame length predictions as well as models of the combustion phase. We will talk in more detail about this category of models in the next few slides. Another group of fire models are used to describe and predict first order fire effects. This series of models includes predicting such outcomes as tree mortality and other immediate, direct effects of fires. First order effects are prompt and local. Lastly, we have models of second order fire effects. Second order fire effects are described by Andrews and Queen (2001) as all other fire effects. These include those that are either far from the burned area or evident after a long period of time.

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Fire characteristic modelsFire characteristic models

• Describing fire behavior models (Pastor et al. 2003)• Nature of the equations

• Theoretical models• Empirical models• Semi-empirical models

• The variables studied• Fire spread models• Fire front properties models

• The physical system modeled• Surface fire models• Crown fire models

The model categories in the framework proposed by Andrews and Queen (2001) are very broad. We will take a closer look at their fire characteristics category, which would include fire behavior models. We will use the categories detailed by Pastor et al. (2003) to help us further understand wildfire behavior models. To start, we will define wildfire behavior models as a single equation or a collection of mathematical equations which provide numerical values for the behavior of the system. Pastor et al. (2003) state that wildland fire models may be classified by the nature of the equations, the variables studied or by the physical system modeled.

They suggest there are three types of models based on the nature of the equations: theoretical models, empirical models and semi-empirical models. Theoretical models are constructed from the laws of fluid mechanics, combustion and heat transfer. Pastor et al. (2003) state that these types of models are difficult to validate but they can be applied to a wide range of conditions.

Empirical models are based on statistical correlation extracted from experiments and other observations. These types of models are only applicable to the systems in which they were developed and only under the same conditions.

Semi-empirical models are constructed from simple, general and theoretical expressions and completed through experimentation (Pastor et al 2003). These types of models can be applied to conditions similar to those that were used to build the model, however there are difficulties in validating the models.

Other classification methods used by Pastor et al. (2003) include classifying the models by the variable studied, such as fire spread models, which include rate of spread and intensity, or by fire front properties such as flame length, flame height or by the physical system (surface fire, crown fire or ground fires).

Most models are best described by a combination of terms that might help you understand how a model works, it’s limitations and it’s applications. For example Rothermel’s (1972) surface fire spread equation is considered a semi-empirical, surface fire spread model.

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Fire spread modelsFire spread models

• Rothermel (1972)

• Byram (1959)• I = HWR,• where

• I = fire line intensity, • H = heat Yield of the Fuel• W = mass of the fuel consumed• R = Rate of Spread

Surface fire spread models are one of the most common modeled systems. These models are the fundamental equation sets used in many of our fire behavior calculation systems such as BEHAVE. The most common surface fire spread model used in the United States was developed by Rothermel in 1972. This model is a semi empirical model which produces a rate of spread value. The model was developed with a theoretical base to allow its application to be as wide as possible. The key concept that fire spread is a series of ignitions, and therefore fire will spread at the rate that fuel can be heated to the ignition temperature. In Rothermel’s (1972) equation, the rate of spread is calculated as a ratio of the heat received by a particle of fuel (the numerator) and the heat required to ignite the fuel (the denominator). You can think of these as the heat source (numerator) and the heat sink (denominator).

The key assumptions made with this model are that the fuel bed is uniform, fires are spreading across the surface and not by spotting, there is no erratic fire behavior, and environmental conditions are constant. Given those assumptions, where do you think this model is applied?

Although this model has been widely used, several limitations have been noted in the literature. Particularly it has been noted that this model is overly sensitive to fuel bed depth especially in mixed fuels and at high wind speeds.

Another equation that is commonly used along with the Rothermel equation is Byram’s (1959) fire line intensity equation. This equation states that the fireline intensity is a function of the heat yield, availability of fuel and the rate of spread.

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The future of fire modelingThe future of fire modeling

• Other types of fire models• Cellular automata models

• The future of fire modeling• Improved understanding of fire related

phenomena• The development of theoretical models

As we end our brief discussion of fire modeling I would like to talk about one other type of model and provide some insight into the future of fire modeling.

One type of model that we have not discussed is a cellular automata model. These types of models are a common approaches to simulate fire growth as a discrete process of ignitions across a landscape. In using these types of models, a landscape is divided into a two-dimensional grid of cells. Each cell is assumed to have a uniform condition. Fire spread is than simulated into neighbor cells using percolation theory to calculate the probability of spread into a neighbor cell. All though these models are not widely used there have been several papers which have used them to look at fire spread across landscapes.

As we think about the future of fire modeling we must consider that the most widely used fire behavior models in the US are based on Rothermel (1972) and Byram (1959), both of which are well over 30 years old. When reviewing the current literature, two key areas appear to lie at the future of fire behavior modeling. Improved understanding of fire-related phenomena such as the transition from a surface fire to a crown fire, and the development and use of theoretical surface fire spread models such as the one of Grishen et al. (1983). The Grishen et al (1983) model is a wind driven model which considers the basic physical and chemical processes of heating, drying, pyrolysis and combustion. This model incorporates chemical kinetics, which allows the model to incorporate the inclusion of conditions under which combustion will not occur (a key feature of this model and of Weber (1991).

World-wide, there are many different efforts to model fire behavior of crown fires. The International Crown Fire Experiment and other efforts have let to innovative modeling approaches very different than those of Rothermel (1972). Some of these reflect rethinking how to represent the processes of heat transfer in models. For instance, the heat transfer within crown fires is that of non steady-state flames.

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Fire as a disturbance processFire as a disturbance process

• We live in a fire environment• Biomass production exceeds decomposition in

most temperate ecosystems • Accumulated biomass fuels fires when there are

ignitions during hot, dry and windy conditions

• Fires have recurred multiple times in the past• Many plants and animals have developed

adaptations to survive and regenerate after fires

Fires are an important ecological disturbance that have shaped the composition, structure and function of many wildland ecosystems. In some ecosystems such as grasslands, fire historically burned often, while in other ecosystems such as subalpine fir forests, fire burned very infrequently. We’ll talk more about how we describe this pattern of recurring fire in our next lesson. In any case though the composition, structure and function of these ecosystems is a reflection of the fire regime. Fire is classified as a disturbance agent because it is a discrete event in time, changes the physical environment, and influences community and population composition, structure, and/or function.

The idea that fire is part of the natural disturbance process leads us to the realization that we do live in fire environments. Almost every terrestrial location has a fire history – fires have occurred and recurred multiple times in the past. In many temperate ecosystems, more biomass is produced than can decompose. Biomass accumulates, and it can fuel fires if weather conditions are right (remember that fuel is one of the legs of the fire triangle) and there is an ignition source (another leg of the fire triangle, oxygen is present in the air so lets assume that one is always present). If the environmental conditions are conducive, fires will spread.

Many plants and animals have adapted to survive in fire environments.

As we have mentioned fire and ecosystems have evolved together over many centuries. As a result, many plants and animals have developed adaptations to survive and regenerate after fires. We will now discuss each of these separately.

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Plant adaptations to firePlant adaptations to fire

• Bark insulation• ponderosa pine

• Vegetative insulation• longleaf pine

• Sprouting• manzanita

• Serotinous cones• lodgepole pine

• Can you think of other adaptations?

Photo By Joseph O'Brien, USDA Forest Service

courtesy of forestry images.

The ability of a plant to survive a fire and/or regenerate after a fire is determined by the life-history, anatomical, and physiological characteristics of the plant, the fire itself (how much heat, where and for how long), and the environment (drought, grazing, competition, etc.).

Ponderosa pine is a species well adapted to survive surface fires. The bark of ponderosa pine is very thick when trees are old and large. The thick bark of ponderosa pine trees protects the cambium from the heat output of a fire (as long as the fire is of short duration) by insulating the cambium from heat. Ponderosa pine has other adaptations to fire as well, including a high, open crown, with long needles.

Many plants survive fire because the meristematic tissue, which includes the buds that are the source of new growth in leaves, cambium, and roots, is protected from the heat of the fire. Longleaf pine has an interesting life stage and morphological features which demonstrate this adaptation. Longleaf pine trees stop height growth soon after seedlings establish and allocate nutrients to the root system during what is called the grass stage (See picture). During this stage the needles are densely packed together around the terminal bud. If a low intensity surface fire burns through the stand, the terminal bud is protected from the heat in two ways. First, the foliage surrounding the bud is high in moisture content and can absorb a lot of the heat. Second, the densely packed needles limit the amount of oxygen around the terminal bud thus limiting combustion.

Many shrubs, grasses and even some trees resprout after fire removes all or part of their crown. Many shrub species such as manzanita have evolved lignotubers. Regrowing shoots draw upon the stored carbohydrates and nutrients in the lignotubers. Many other shrubs and grasses resprout from rhizomes (these are underground stems), the root crown, the basal caudex, or other structures at the base of the plant.

In tree species with serotinous cones, the mature seeds remain in the cone – the cone doesn’t open because it is sealed by resin. When the cone is heated enough in a crown fire, the resin melts, the cones open and many seeds are released. Lodgepole pine has serotinous cones some of the time and in some places.

There have been many other fire adaptations suggested such as seed dispersal mechanisms. Can you think of some examples of other adaptations?

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Animal adaptations to fireAnimal adaptations to fire

• Escape• Burrow• Life stage and life

history

Just like plants animals, have also evolved with fire. Some have developed adaptations or strategies to survive fire as well. The most obvious tactic for surviving a fire is simply to avoid the fire. Animals can avoid the effects of fire by simply moving away from the fire front, or they can seek refuge in an area that has not been burned as seen in this picture. This strategy is only useful however if the animal can get away from the fire and smoke. Species like deer and elk which are fairly mobile often use this tactic. Birds also use this tactic if they are old enough to fly. We will talk about this more in a little bit.

Other animals, such as mice or reptiles, probably cannot move fast enough or far enough to avoid the fire front, so they must use another strategy. One strategy is to burrow into the ground for protection. Although some may consider this an escape mechanism we will discuss it separately for now. When an animal burrows into the soil, the soil absorbs the heat. Animals do not have to burrow very deeply to escape the heat.

Last I would like to talk about how life stages and life history may help animals survive fires. Life stage may be important in the ability of many species to survive fire. For example, nestlings will not be able to fly to a refuge or unburned area. Kruger and Bigalke (1984) provide one of the only case studies of a vertebrate using life history to survive fire. They show how the geometric tortoise lays eggs in the spring which are buried in the soil. The eggs remain in a incubation period throughout the fire season protected in the soil, than hatch in the fall once the fire danger has been reduced. Other animal attributes which may help survive fire are body size and fur. Think about how body size and amount of fur may help an animal survive in terms of the principles of heat transfer.

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Ecological implicationsEcological implications

• Injury, mortality, susceptibility to other disturbance agents

• The lethal temperature of living, unprotected tissue is ~60C for 1 minute

• How do plants ever survive fires then? (Hint: think in terms of heat transfer) I-90 fire west of Missoula, Aug 2005,

photo by Sarah Bunting

As a result of fire, individual plants and animals may die, they may be injured or otherwise weakened and therefore become more susceptible to insects and other disturbances.

We will begin by discussing mortality. For the purpose of this course we will consider mortality to be the death of the entire plant. Unprotected plant tissue dies when heated to about 60 degrees Celsius is applied for one minute. Note that this is a general rule of thumb, and that some tissue, like dry seeds, can take higher temperatures. If enough tissue is killed during the fire the plant will eventually die.

Many studies have been conducted to predict mortality of trees from fire based upon the type and degree of injury from fire. We will define plant injury as the death of any plant material. The injury of plant material can than increase the susceptibility of the injured plant to other disturbance agents such as insects or pathogens, which can than lead to mortality of the whole plant. The relationship between fire and other disturbance agents is not well understood in many ecosystems but can have important management implications.

When we think about the idea that plant tissue dies when temperatures are raised to 60C for 1 min, then how do you think plants ever survive fires? To answer this question we need to think in terms of heat transfer principles. As we have discussed, plants commonly survive fire when their meristematic and other living tissues are insulated from the heat of the fire. For example, the roots can be insulated by soil, and the cambium can be effectively insulated if the bark is thick enough and the fire passes quickly (short duration of heating). If trees are tall and the lower branches have died the base of the live crown may be well above the flames and the heat

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More ecological implicationsMore ecological implications

• With these simple ideas, explain:• Why small trees are more

susceptible to fires than big trees (assume the only difference is size of the tree)

• Why most shrubs and grasses and forbs are top-killed by even short flames

• Why many plants can resprout after fire

• Why are crown fires (those where the biomass in the tree and shrub crowns are the fuels that burn?) more likely to kill trees than surface fires?

I-90 fire west of Missoula, Aug 2005,


Let’s continue to think in terms of heat transfer principles to address these questions.

Why do you think small trees are more susceptible to fires than large trees? Small trees often have thinner bark (less insulation of the cambium). They are also short (so their living tissue is often heated beyond lethal temperature from direct heat contact or convective and radiative heating).

Why do you think most shrubs, grasses and forbs are top-killed by even small flames in a fire? Most shrubs and grasses and forbs don’t have insulating bark that is thick enough to protect the cambial tissue from heating, and they aren’t tall enough to have their buds and other living tissues in the crowns above the flames even when the flames are small. They have to resprout or reestablish from seeds stored in the soil, the soil “seedbank”, or from seed that reaches the site from off-site sources.

Why do you think so many shrubs are able to resprout and become established after a fire? The buds that give rise to new tissue are often protected by soil (a poor conductor of heat), and the buds are often stimulated to grow in the post-fire environment.

Why do you think crown fires are more likely to cause tree mortality than surface fires? In crown fires, the buds that give rise to new tissue and the leaves are subjected to the temperatures inside flames (via convection, radiation, and direct consumption) which are well over the lethal temperature of living tissue. In a surface fire the cambium is protected by the bark and the crown tissue is protected

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More ecological implications questions More ecological implications questions

• Why are ground fires more severe than surface fires, even though they burn less intensely?

• Why are animals that burrow into the ground more likely to survive than ground-nesting birds?

I-90 fire west of Missoula, Aug 2005,


OK. More questions. Think like a fire ecologist. Why do you think a ground fire is more severe than a surface fire even though it burns with less intensity? Surface fires burn organic material on (above) the soil surface. Ground fires burn organic matter that is part of the soil (think of a peat fire such as one that occurs in a wetland dessicated by drought). In ground fires, the soil itself is heated at the depths and to the temperatures that are often lethal to living tissue. (Also, the organic matter is important in holding water and nutrients and insulating the soil and so making conditions more favorable for some organisms).

Lastly lets think about why animals that burrow into the ground are more likely to survive a fire than a ground-nesting bird? Soil is an insulator and therefore protects the animal from extreme heating, though some may die from inhaling hot gases.

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Key pointsKey points

• The power of thinking about the underlying mechanisms for fire and fire effects

• Terminology• Crown, surface and ground

fires• Meristematic tissue and

insulation• Plant adaptations to survive

fires• An introduction to fire intensity

and burn severityI-90 fire west of Missoula, Aug 2005,


These are some of the key points I hope you got out of this short presentation.

I hope that you’ll bring this search for underlying mechanism and it’s implications to our further studies of fire ecology. I will keep asking you to focus on the underlying processes – the how and why of what you observe about fire effects.

I’ve introduced lots of new terms. If these terms are unfamiliar, you need to review them. Be sure that you can define them, give examples to illustrate your understanding, and be able to compare and contrast similar terms. If you have trouble with terms, look in the textbook for explanation, check out the ecology module that we put together for you, and ask one another for help.

We’ll talk about fire intensity and burn severity in upcoming lectures as we explore fire history and fire regimes, and again as we think about vegetation response in each of the different ecosystems we’ll study during this semester.

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Literature CitedLiterature Cited

• Andrews, P.L. and Queen L.P. 2001. Fire modeling and information system technology. International Journal of wildland Fire. 10: 343-352

• Byram, G.M. 1959. Combustion of forest fuels. In Davis, K.P. (ed.) forest fire: control and use. McGraw hill NY, NY. 65-89

• Grishen, A.M., Gruzin, A.D. and Zverev, V.G. 1983. Mathematical modeling of the spreading of high level forest fires. Sov. Phys. Dokl. 28. 328-330

• Latham, D.J. and Rothermel, R.C. 1993. Probability of fire stopping precipitation events. USDA Forest Service Research Note INT-410

• Pastor, E., Zarate, L. Planas, E. and Arnaldos, J. 2003. Mathematical models and calculation systems for the study of wildland fire behavior. Progress in Energy and Combustion Science. 29: 139-153

• Pyne, S.J., Andrews, P.A., and Laven, R.D. 1996. Introduction to wildland fire. John Wiley & Sons NY, NY. 769 pp.

• Rothermel, R.C. 1972. A mathematical model for predicting fire spread in wildland fuels. USDA Forest Service Research Paper INT-115.

• Weber, R.O. 1991. Modeling fire spread through fuelbeds. Progression in Combustion Sciences 17: 67-82

Here’s the information you could use to find the references Chad Hoffman and Penny Morgan cited in this presentation.

None of these are required reading.

We do expect you to read the related chapters in your textbook. You can expect questions on the exam that require you to understand and apply what you’ve learned here today.

for 426 fire management and ecology - university of idaho

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