Different vegetation types burn differently. The characteristics of the vegetation will influence the intensity and spread of a bushfire. To understand how a bushfire might spread, it is important to consider the following features.
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Fuel quantity is the amount of fuel at a given location. For example, a dense forest has more fuel than an open forest. Fuel quantity is also called fuel load and is measured by the amount of fuel per unit area (e.g., tonnes of fuel per hectare).
Fuel quantity describes the amount of fuel at a given location
Fuel type is a way to categorise fuels into groups which influence bushfires in the same way. There are seven main vegetation types (called Classified vegetation types) in Australia. In Victoria, some of the more common (and bushfire prone) vegetation types include grassland, scrub, and woodland.
There are several different vegetation (fuel) types in Australia
Fuel size and shape
Fuel size and shape influence how quickly a fire can ignite and how long it will burn. For example, grass and twigs are considered fine fuels which ignite and burn very quickly, whereas heavy fuels like tree trunks take more time to ignite and will burn for a long time.
A fuels size and shape will influence how it burns
Fuel arrangement describes how fuel is arranged at both large (the level of individual trees) and small (the level of the forest) scales. For example, at the large scale, Cypress trees have lots of dead highly flammable fuel inside the tree, which means they can ignite and burn very quickly.
The arrangement of the fuel will influence how it burns
Moisture content is a measure of how much water is contained within the fuel. Dry fuels ignite and burns quickly, while wet fuel is difficult to ignite. Moisture content is strongly influenced by climate and local weather conditions, but is also determined by the characteristics of the individual plant species – some plants are naturally dryer than others.
Strong winds, high temperatures and low humidity will decrease moisture content