Introduction to Fire Ecology

Consider the statement: “Fire is bad” – What do you think? Why? – Can you think of examples of when fire is good and bad? What are they?

Fire is a natural component to many ecosystems – Both plants and animals – Interactions among organisms

What is Fire Ecology? A branch of ecology that studies the origins of wildland fire and its relationship to the biotic and abiotic environment. Fire is studied as a natural process operating as a component of an ecosystem. Fire, similar to floods, earthquakes, and storms, is just one way of promoting change in an ecosystem.

Fire ecologists study: – the origins of fire – what influences the spread and intensity – fire’s relationship with ecosystems – how controlled fires can be used to maintain ecosystem’s health

Physical and Chemical Properties of Fire What does it take to ignite a fire? – Oxygen at ignition point or kindling temperature Woods has to reach 800 ◦ F to burst into flames – As wood is heated, it is dried of water while oil and resins are boiled away – Chemical structure of wood is broken down and flammable gases are produced Flaming combustion

Physical and Chemical Properties of Fire Flaming combustion causes the surface of the wood to become charcoal At cooler temps, glowing combustion consumes 3 molecules – Charcoal, water, carbon dioxide

What influences the probability of ignition and combustion? – Fuel – Weather – Topography – Fire history

Forest Fuel Layers

Fire Behavior Mostly described by its intensity and the area it spreads to

Factors influencing intensity Available fuel – Quantified by size and arrangement – More fuel, more intense

Factors influencing intensity Moisture and temperature – Cool, moist fuels combust more slowly than hot, dry fuels

Factors influencing intensity Fuel composition – Can make fire more or less intense – Oils and resins increase heat yield of reaction and burn more intensely – High concentrations of minerals can reduce flammability

Factors influencing intensity Wind – Increases oxygen supply – Can produce “spot” fires

Factors influencing intensity Topography – If fire at top of slope, fire will burn slowly downhill – If fire at bottom of slope, fire will burn quickly uphill

Factors influencing spread – Fires in dry, windy conditions with ample fuel spread rapidly – Fuel continuity – Topography Rivers and lakes can act as fire breaks – Composition of plant community Some plants are more flammable than others

Effects of Fire on Ecosystems 1. Mosaic Patterns – Burn Mosaic Wildfires create areas of total burn, partially burned, and unburned sections – Result from factors like wind shifts, chemical composition, temperature changes – Varied regrowth rates of vegetation

2. Soil Conditions – Fires can be both good and bad for soil – Nutrient levels can increase due to: Mineral content of ash and charcoal Warm, moist conditions which increase microbial activity – Intense heat can cause soil to become water repellant Causes run off and erosion

3. Animal Populations – Some will perish during fire especially smaller, older, weaker animals and insects – Larger animals can leave area – Populations tend to suffer more after fires due to loss of food source Most fires tend to be before winter – Predators have advantage since groundcover is gone – Scavengers find increase in food – Some animals, like deer, will eat nutrient rich charcoal – Birds benefit Increase in seed availability Nesting sites increase due to snags (dead standing trees)

4. Plant Populations – Vegetation composition determines how fire behaves Fire behavior in turn determines how plant population is affected – Fire decreases competition to survivors – Increases nutrient, water, and light availability – May rid plants of their parasites (e.g. mistletoe) – Plant adaptations allow to survive and reproduce Sequoia has thick bark to protect Chaparral shrub needs fire to open seeds

Thick bark of Sequoia tree Chaparral seeds need fire to be released

Fire Regimes Regimes are patterns in wildland fires that include frequency, extent, intensity, type, and season Varies among ecosystems due to their composition and structure – Influenced by climate, vegetation types, and ignition source

Ecologists will study evidence to determine historical fire records or natural fire regimes – Sample fire scars on trees Sequence of fires on growth rings – Sample sediments from lakes and reservoirs – Current weather – Written and oral histories – Fuel build up – Lightning fires

Based of those factors and the ecosystem, ecologists will use the most appropriate management regime. Various management techniques will be used. One technique does not fit all habitat types.

Human influence on wildland fires Humans have one of the greatest influences on ecosystems Humans have altered natural fire regimes – Native Americans and early settlers used fires in their management practices – Today will use fire to clear lands for housing, agriculture, and roads

Prescribed Burning Fire Suppression – One of the fires management practices – 1930’s researchers began to challenge policy Possible benefits to ecosystems – 1950s and 1960s the national forests began to experiment with prescribed burning Prescribed burning = starting fire on purpose

Prescribed Burning (continued) Prescribed burning – Restore natural fire regime in area where suppression had been practiced – When reintroduced to ecosystem, takes time for ecosystem to adjust – Use low intensity fires – In areas where there is potential for high intensity fires (fuel and wind), this practice is not has useful

What effects does Fire have on an ecosystem? Depends on its intensity Hotter, longer lasting fires have more extensive effects than cooler, short-lived fires Pros Return nutrient to the soil Encourage plant diversity Prevent insect attacks Burned areas provides snags for wildlife Cons Soil erosion Food for wildlife, humans destroyed Kills trees, vegetation, wildlife Very hot fires remove all roots, seeds, and soil organisms for tree growth