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)
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))
What makes plants flammable?
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?
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?
Resprouting is uncommon in confiers, which species are an expception to this?
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)
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
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?
What is the fire interval for central Alaska black spruce forest?
And Alaska white spruce forest?
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
What is the mortality rate of the understorey cohort like?
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.