Fire Ecology



In what time period did the combination of grasses and fire begin to help create the open plains?



Mesozioic (100 mya+)


How many tonnes of plant carbon does fire consume annually in the tropics alone?



2700-6800 million tonnes



What is causing the evergreen forests of Hawaii to shrink?



The spread on non-native grasses and the fires they generate



What is swaling?


Small controlled burns set in later winter and early spring to avoid the larger fires which would otherwise break out in the summer.



How much of plant production do insects and vertebrate herbivores consume each year?





How much above ground primary productivity can fires consume?





Fynbos shrublands (South Africa) have above ground productivites of 250gm-2yr-1. How much does it loose to fires once every 15 years?






What features of plants that reduce herbivory promote fires?



tough, fibrous, long-lived leaves



What is a simple fire regime made up of?



Frequency, season, intensity



What are the three types of fire?



Ground fires, surface fires, crown fires


What are backfires?


Fires that burn against wind or downslope

– These are more intense



What are headfires?



Fires that burn with the wind or upslope – These are less intense


List the important vegetation types in order of fires least frequent to most frequent

South American Rainforests (fires infrequent)
Californian Chaparrel Shrublands (25-100 years)
South African Fynbos Shrublands (5-40 years)
African Savannas (1-30 years)
North American Coniferous forest (1-10 years, crown 1-1000y)

Brazilian Cerrando (1-3y)

Australian Euculyptus Woodlands (Annualy at surface, crown 100-300y)

Grasslands (Annually)



Which vegetation type has the highest recorded intensity of fire



Australian Euculyptus Woodland – crown fire 7000-70000 kWm-1



What are the fire intervals of grasslands and African savannas dependent upon?


Rainfall and grazing pressure which determine fuel load


What are the prequisites for fire?


Weather conditions (needs to be dry, climate influences fuel accumalation, lightening generates fire)

Source of ignition (lightening, spark from rocks falling, volcanic activity, humans (last 1my))

Sufficent fuel


What makes plants flammable?


Moisture content

Surface to area ratio

Energy content (levels of oils, fat, waxes & terpenes)




Name three plant types that are fire-prone. Why are they fire-prone?


Pines, grasses and heaths, because they have finely divided leaves that increases their surface area to volume ratio


What are the factors that need to be taken into account when looking at flammability of plant communities?


Fuel types (dependent on moisture content)

Surface are to volume ratio of fuel type

Packing ratio (fuel to air mixture)

Mean fuel energy content for combined fuel mass



What makes coniferous forest understoreys burn with smaller flames and lower intensity than grasslands, depsite much bigger fuel loads?



Because of the dense packing ratio of the fuel bed



Why don’t broad-leaved forests of North America support crown fires?



Because of the high moisture content (140-200% moisture content)



What is the moisture content of coniferous forests?





Why do eucalyptus woodlands burn with greater intensity than similar vegetation types?



Because of the high levels of flammable compounds



Why don’t rainforests burn? (2 reasons)



Because they are too wet and have a high turn over of litter and so don’t accumulate much dead fuel



Why do meditteranean shrublands burn frequently despite high rainfall?



Because of extremely slow decomposistion and so there is a build up of dead fuel. Also because there is low levels of herbivory.

What are the two major threates of fire to trees?



Canopy scorch

Damage to the cambial tissue beneath the bark


What does vegetation survival depend on?

Bark thickness (to protect cambium)


Crown architecture (fast-growing species can grow out of reach)


Resprouting from buds



The ability to resprout it widespread in which group of plants?



The Angiosperms


Resprouting is uncommon in confiers, which species are an expception to this?


California redwood


Jack pine


Give to species examples which resprout from roots resulting in large clonal populations after fires


Aspen and birch in boreal forests



Why are grasses amongst the most fire-resistant?



Because of their ability to resprout at ground level


Most fire-prone communities are dominated by plants with thin bark and lack the ability to resprout. So how do they survive fires?



Their seeds survive the fire


What does fire stimulate in fire lilies?




(Usually plants that suffer little material loss can redirect resources to reproduction rapidly)



Explain serontiny

Some species accumulate seeds in a seedbank stored in the canopey, insulated from fires by cones or other woody structures. They only open and release seeds after fires.



In the Northern hemisphere what are the only serotinous species?






What species are serotinous in the Southern hemisphere?


Many angiosperm families e.g. Euculyptus regnans


What is the self-regulatory hypothesis?



Density-dependent feedbacks determine population size



What is the Fire Interval hypothesis?


Variation in the fire return interval interupts the normal pattern of growth, mortality and reproduction. And so the duration of these normal growth phases determines the state of the population when it is burned



What is the Event-dependent hypothesis?


The circumstances of each fire are unique. The same fire interval may produce very different population effects depending on the nature of the fire.


What are the effects of longer fire intervals?

They allow more time for density-dependant feedbacks to take place

They allow for fuel accummulations which resultom more intense fires which impact survival and reproduction


What are the three “Vital Attributes” that affect the likley success of species in a disturbance dominated community?

1. Some species able to survive, some are killed but can reconolise elswhere afterwards

2. The ability to establish and grow to maturity in the developing community (competition)

3. The duration of certain phases of the life cycle (time to reach reproductive maturity etc.)



Why are fire-prone communites containg sprouter and non-sprouters dominated by non-sprouters?


Because sprouting comes at a considerable cost resulting in reduced seedling growth rates and defferred reproduction. 

Non-sprouters therefore have a reproductive advantage over sprouters


Why have individuals evovled to become more flammable?


Too remove neighbouring competition and then resprout


Name four examples of fire management practices


Livestock production



Reduction of fire hazards


Why are boreal forests unusual amongst fire-dominated communities?

Because fires move through the canopy rapidly causing substantional mortality and the rate of spread causes large areas to be burnt at once

The nature of the litter allows fire to burn deep exposing expansive areas of mieral soil

The frequency with which fires return is often about half the natural span of the trees


How many fires burn each year in the coniferous forests of Canada?





How many hectares of boreal forest are affected by fire annually? What percentage of the forest is this?


2 million hectares



What is the average fire interval of a boreal forest?


60 years


What is the fire interval for central Alaska black spruce forest? 

And Alaska white spruce forest?


36 years

113 years


Why are jack pine and lodge pole pine especially prone to fire?


Because they are associated with well-drained, sandy soils


What is the fire interval in Montana


50 years


What is the mortality rate of the understorey cohort like?


Constantly high


What is the Fire Weather Index based on?


The weather conditions and drying rates of different types of fuel


What is the moisture content of deciduous trees and conifer trees?


More that 150% and lower than 100%


What effect does fire have on low bulk density and shallow duff?


If the surface ignites it could ignite lower levels


What effect does a high bulk density and deep organic layers have?


It protectes lower layers from igniting. A very intense fire would be required to drive off the water and consume the entire profile.



What fuel do most forests consist of?

Duff – litter soil horizons

Surface fuels – needles, leaves, mosses, lichens, herbaceous vegetation, shrubs, tree seedinlings, branches

Crown layer fuels – live foliage, branches

Ladder fuels – provide vertical continuity between fuels


What percentage of burnt patches are larger than 10,000 ha? And what percentage of burned areas do they account for?


3% and 90%


Number if unburned patches increaseas per hectare as fire size decreases or increases?




What are the three types of crown fires in boreal forests? With explanations

Passive crown fires – drop from crown to ground, and don’t spread far, trees generally survive

Active crown fires – ground surface into crowns. Most common form and causes mortality

Independent crown fires – spontaneous, independent of surface fires and spread rapidly


Why are Jack pine and Lodge pine the only species in boreal forests that can survive repeated scorching?



Because they have thick bark


At what tempreture does the resin of Jack pine melt? And to what tempreture can the seeds survive?


60 degrees celcius

150 degrees for 35-45 seconds and 370 degrees for 10-15 seconds


Describe invadors


Species that are usually shade-intolerant such as fireweed and some mosses whose seeds and spores are readily dispersed by wind



Describe Envadors


They regenerate even in killed e.g. Jack pine & Lodgepole pine with serotinous cones, and bristly sarsapanilla, pink corydalis which long lived seeds


Explain Avoiders


conifers such as white spruce and balsan fir killed by fire, regenerate through seed input from individuals missed by the fire. Shade-tolerant mosses and lichens also do this


Explain resisters


Species that are protected against fire e.g. the shoots of cotton grass are protected by dense tussocks


Explain Endurers


E.g. Trembling aspen – the canopey is killed by fire but regenerates from underground organs