Effect of Forest Fires in Eastern No. America

The forests of eastern North America exhibit considerable variation in both their composition and their response to natural fire. As one progresses from north to south, these forests range from boreal and mixed coniferhardwood to deciduous. Throughout this range, forest fire can have a number of different effects.

Fire is a natural force which is actually required by the many dynamic processes of forest regeneration (Ripper, 1989, p. 36). Forest fire purges mature forests of various pests (Brosnahan, 1990, p. 69). For example, smoke kills the Tussock moth and spruce bud worm (Ripper, 1989, p. 36). Fire also converts tree needles and other forest floor debris into nutrientrich beds. These areas promote the growth of seedlings. Finally, many plant species actually incorporate periodic conflagration into their reproductive cycles.

The primary cause of natural fires is lightning (Johnson, 1992, p. 6). In some areas, it accounts for 90% of areas burned. In order for a large fire to occur, a number of circumstances must be present (Johnson, 1992, p. 11). For one, the wood fuels must be dry enough to burn. Then, there must be ignition. Finally, wind is usually necessary for fire spread.

These factors can only occur in the right sequence when specific meteorologic conditions prevail. Thus, critical fire weather is associated with a "characteristic persistent 50 kPa (500 mb) longwave ridge

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forest growth. All northern tree species seedlings do well in mineral soils (Johnson, 1992, p. 100). Farther south, hardwood fires can actually enhance forest growth. These forests often have a dense understory of shrub species (Patterson, 1992, p. 34). The shade tolerant plantsmany of which have been imported from other parts of the worldcan make survival difficult for deciduous seedlings. "Cool" surface fires of the hardwood forests clear out this shrub layer (Reich et al., 1990, p. 2179). Furthermore, they tend to have a lesser effect on the larger trees, and may actually increase nutrient availability. Thus, fires in hardwood forests suppress intolerant species while providing opportunities for the reproduction and growth of the survivors (Matlack et al., 1993, b., p. 119). In fact, in many deciduous forests wind is the principal cause of natural disturbance (Matlack et al., 1993, a., p. 1559). In the more southerly areas, fire may consume herb and shrub level vegetation but only high winds damage the forest canopy. Only occasionally may fire injure a tree and thus make it vulnerable. Under noncatastrophic conditions the structure of eastern hardwood stands is largely determined by regeneration in gaps creat
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