Factors affecting the behavior of wildland fires
Fuel can affect the fire’s behavior based on the nature of the grass. Short dry grasses will flash over once and contribute little to the fire, while short dry grasses will not burn, but dry out and finally burn when the moisture content dries up and provides fuel for a reburn. For long dry grasses, the tops of the grasses will burn first, leaving the stems for a reburn if the fire is a fast-moving one. While a slow moving fire would end up burning the grasses to their stems causing the top of the grass to fall.
For brush and heavy timber, the fire may ignite the tops of the trees first, called crowning. The heavier portions of the tree may then ignite later as the fire conditions change. Heat transfer through radiation may also cause trees nearby to be raised to their ignition temperature where upon they will conflagrate into flames.
The make up of the fuel will also affect the nature of the fire. They may affect the spread of the fire and its intensity. Trees with high resin content such as firs and pines, will result in unusually fierce and intense fires. Some trees will die when the living layer of cells just beneath the bark, the cambium, gets damaged. Trees have adapted some rather interesting ways to resist damage. Some trees also have the ability to resist fire such as the giant redwoods, which have a thick huge bark to resist fire. Others may contain a high oil or grease content in the wood, shielding the tree from the hot and intense environment. Fire burning on this fuel would be extremely intense even to the point of causing the oil contents in nearby plants to volatilize, resulting in the formation of flammable vapors.
Another aspect of the fuel to take into consideration will be the moisture content. The greater the moisture content, the more difficult for it to conflagrate. The main difference is whether the moisture is internal or external. Trees with external moisture will be resistant to the first pass of the fire, however, on the second pass, it will be fuel ready for ignition if the heat from the first pass evaporates the moisture. For the internal moisture, the external moisture will be affected more slowly because it achieves equilibrium with the atmosphere via the surrounding cells. This would affect the moisture content in such plants at a much slower rate. However, there are instances where fires were able to reduce the moisture content in such plants in a rather rapid rate.