Forest Fires: Their Effect on the Forests of Eastern North 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 conifer hardwood 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 nutrient rich 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 and its breakdown" (Johnson, 1992, p. 14).
Typically, this weather occurs due to westerly flow disturbance along the Arctic front. At the surface, the resultant anticyclones (high pressure areas) bring periods of high temperature and low humidity. This weather may last anywhere from a few days to a month.
High pressure ridges tend to develop over Alaska, the Yukon and the Northwest Territories of Canada. As summer progresses, the center of ...