Available Fuel

Available fuel consists of all biomass (vegetative material) that can be ignited by a heat source under optimal burning conditions (Wade, 1989)(Helms, 1998).  Measuring the available fuel will determine the fuel load and determine a risk associated with a particular stand of trees.  Fuels become available as a result of climate, weather and topography.  Climate determines the growth rate of plants, and therefore the rate of fuel accumulation due to drying out an/or dieing.  Increased rainfall and relative humidity will decrease the likelihood of fire ignition or the spread of fire.  Wind can dry and add oxygen to fuels, causing spot fires ahead of fire fronts. Topography creates habitats for different vegetation types, each with different fuel characteristics. (Need Citation).                                                                                                                                          

Fuels are categorized in seperate classes; for example, fuels are grouped in vertical layers, and fire will act differently in each vertical layer, explained below.

1. Ground Fuels include the duff layer, roots, and buried or partially buried dead and decaying logs.  Ground fire spread is usually slow due to the compactness of ground fuels, with burning by smoldering combustion (Debano, 1998)(Add Citation From SAF Book).

2. Surface Fuels include standing trees, herbaceous plants, litter, and downed woody material.  Most fire in natural ecosystems ignites and is travels through surface fuels (Debano, 1998)( Need Other Citation).

3. Crown Fuels are tree and shrub crowns.  Even when the crowns are not burning, they can affect the behavior of a fire in surface fuels.  For example, forest stands with open crowns generally have faster spreading surface fire than those with closed (dense) crowns because of increased airflow (Debano, 1998)(Need Other Citation).