A wildfire is an uncontrolled fire that occurs in natural vegetation such as a field, brushland, or the forest. Oftentimes these conflagrations are referred to as a field fire, brush fire, forest fire or mountain fire, depending on its location. Wildfires thrive where there’s lots of dry vegetation.
The US Forest Service standardized three main classes of wildfires depending on where the fire is burning: ground fires, surface fires, or crown fires.
Ground fires burn below the surface. Examples of ground fires may be duff fires, fires in coal seams, or fires in a peat bog. They tend to burn slowly, smolder, and can burn for very long times, especially if they are burning in a coal seam or peat bog. These fires inch along and sometimes go unnoticed unless they send up a lot of smoke or create enough heat to ignite surface fuels like leaves or sticks to start a surface fire.
Ground fires can be very destructive to the health of vegetation because they can consume roots, beneficial bacteria, or fungi. In Frederick County, we tend to see ground fires during very dry conditions when the drought index is high. These fires are hard to extinguish, and it normally requires the digging of a deep fire break below the humus layer of soil, down to bare mineral soil. A fire plow may be used on large fires during dry conditions.
This tool will dig a 2-foot ditch around a fire to halt the spread of ground fires. Most of the fires that we see in our area are surface fires. Surface fires consume most of the flammable material on the surface. Normally, most of the fine material such as leaves sticks, moss, etc., can burn in a surface fire that is not very hot. However, when a fire gains momentum or when fire conditions are severe, the heavier fuels such as large logs, shrubs, and dead standing trees begin to ignite.
When this occurs, the fire increases in intensity and is harder to extinguish. These higher intensity fires give rise to ground, and sometimes, to crown fires.
A crown fire is one that reaches into the crowns of trees and can be very intense. Crown fires are more common where the predominant trees are evergreens, since evergreen foliage has volatile oils and resins which will ignite when it becomes hot enough. Crown fires are more common in the western states, but they can occur in elsewhere if the evergreen component is large enough.
A surface fire may start to crown when it is driven by hot dry winds, is burning uphill, or where there are fuels that cause the flames to ladder up into the tree. Some of these ladder fuels may be small dead trees, vines, or understory vegetation that have volatile flashy fuels. A fire burning the whole of the tree can create strong updrafts which can send burning embers high into the sky where they may drift for considerable distances before falling back to the ground.
These burning embers may start spot fires far away from the leading edge of the fire. Spot fires are very dangerous, especially for fire fighters because they can result in the unpredictable spread of the fire. Locally, a single hollow dead tree, also known as a snag, may candle (burn from the inside) and send embers out, starting new spot fires. For this reason, removing dead ladder-type fuels and felling burning snags is a high priority activity during forest fire fighting.
Wildfires can threaten life and property. One way to lessen the risk of a large fire is to reduce the fuel loads. In an effort to protect houses and western rural communities, the Federal Government has implemented a program that targets fuel loads and volatile plants. This will reduce the chance that severe wildfires will threaten these areas.
Article by FCFCDB
Nature Notes for 6/21/2015