| Latest Update -- Tuesday, September 12, 2000
Most backcountry trails have also reopened to day and/or night use. However, some trails in the Bechler area that are in close proximity to fires do remain closed. Visitors planning to day hike or stay overnight in the backcountry are encouraged to call the Backcountry Office at (307) 344-2160 for specific trail closure information and other possible restrictions. Yellowstone’s fires are located in remote backcountry areas and are not threatening any developed areas at this time. Following is information on current fire activity in the park. There are approximately 17 people assigned to Yellowstone fires. The Plateau Fire, located in a remote area of the southwestern portion of Yellowstone near Boundary Creek, is estimated to be 2,800 acres. This fire continues to have some activity along the northeast boundary of the fire but none along the western boundary. It is putting up very little smoke and is not threatening any developed areas. This fire continues to be monitored. The Moose Fire, located near Moose Creek south of Shoshone Lake, is estimated at 1,300 acres. There has been little activity and little smoke on this fire, and some snow was noted in the area on September 6. Previously burned areas from the 1988 Yellowstone fires are helping to naturally keep this fire from significantly spreading. This fire continues to be monitored. The Boundary Fire is located along the South Boundary of the park near Grassy Lake. This fire is estimated at approximately 380 acres. No smoke was visible from this fire on September 7, 2000; the fire will continue to be monitored. The Unlucky Fire, located in the southwest portion of the park in the Bechler area, also received a trace of snow on September 6. It is now estimated to be approximately 2,700 acres. This fire is mostly burning in fuels within its perimeter and is putting up a small amount of smoke. It is not substantially expanding. It is being monitored. There have been a total of 34 fires during the 2000 fire season, 4 of which were human-caused; the remaining 30 were lightning-caused. All of these fires, except those mentioned above, have been declared out. In an average year approximately 15 fires are ignited in Yellowstone by lightning, burning about 4 hectares (10 acres) total. About 83% of naturally ignited fires in Yellowstone never reach more than 0.5 hectare (1.2 acre) in size. About 94% of fires in Yellowstone never burn more than 40 hectares (100 acres). In Yellowstone, on average, fires are detected at 3:03 in the afternoon-- fires burn most vigorously during the heat of the day, causing tall smoke plumes to be seen by fire lookouts or sharp-eyed park visitors.
Although many fires were caused by human activities, most ignitions were undoubtedly natural. The term ‘natural ignition’ is nearly synonymous with a lightning strike. Afternoon thunderstorms occur frequently in the Northern Rockies but release little precipitation, a condition known as dry lightning. In a typical season there are thousands of lightning strikes in Yellowstone. Lightning strikes are powerful enough to rip strips of bark off of a tree in a shower of sparks, and blow the pieces up to 30 meters (100') away. However most lightning strikes never result in a wildfire because fuels are not in a combustible state. Fuels are typically wood, foliage or grass. Fuels may be fine, such as twigs and needles, or heavy, such as logs, branches and whole trees that have blown down in a storm. Fuels may also be living such as an understory layer of tree regeneration or a layer of shrubs. In order for an ignition to take place, the fuels must be dry. As spring advances into summer, temperatures increase and the relative humidity decreases-- factors which dry fuels. On average in Yellowstone, fuels dry out enough to ignite the first wildland fire of the year about the middle of June. Young forests generally do not have the fuel loads that mature and old-growth forests do. Many young stands grow on old burn sites in which accumulated fuels have burned off. However, as a stand develops it accumulates fuel: needle-cast, fallen branches, lichens, and logs. As the young trees grow they compete for light and other resources. Many don’t survive the competition, and remain in the stand as standing dead snags which fall over and further contribute to the fuels on the forest floor. As trees grow they also ‘self-prune’ old branches that become shaded by new foliage at the top of the canopy. These pruned branches eventually fall off the tree and accumulate as litter on the ground. As the stand grows older and taller the canopy begins to break up, letting light reach the forest floor and allowing the establishment of an understory layer of shrubs and regenerating trees. This understory layer forms a ‘ladder’ of fuel that may allow a ground fire to ascend into the forest canopy. This accumulation of fuel on the forest floor and the continuity of fuels between the ground, understory and overstory are factors that predispose older stands to ignition by a lightning strike. Nearly all of Yellowstone’s plant communities have burned at one time or another. Some plant communities ignite and carry fire more readily than others. Therefore the ‘fire regime’ of Yellowstone is as varied and complicated as the environments within the park. It must be remembered that any forest will burn provided an ignition during periods of prolonged drought, high temperatures, low relativity humidity or high winds. However each type of forest has certain characteristics that cause wildfires to behave differently. Some trees such as Douglas-fir have very thick bark that insulates the tree against heat. The bark protects the cambium (the water and nutrient conducting system between the bark and the wood) which will die if it is exposed to temperatures greater than 60°C (140°F) for longer than 1 minute (Agee 1993). Thick bark ensures that wildfires seldom to kill mature Douglas-fir trees. Other species such as lodgepole pine, whitebark pine, Engelmann spruce and subalpine fir have thin bark but these species have other adaptations to fire. Lodgepole pines have cones that are serotinous; that is, they are glued shut by resin. The heat of a wildfire is needed to melt the resin and allow the cone to open and disperse the seeds within. This adaptation ensures that the seeds of lodgepole pine will not disperse until wildfire creates conditions that favor the establishment of seedlings-- diminished litter on the forest floor and plenty of sunlight. Although whitebark pine, Engelmann spruce and subalpine fir are also thin-barked, they are adapted to fire by escaping, that is they grow in habitats that are less susceptible to wildfire. Whitebark pines grow in open, cold, high altitude habitats that accumulate fuel very slowly. The length of the growing season between snowmelt and snowfall, and the cooler temperatures leave a short seasonal window in which wildfires can ignite and carry. Engelmann spruce and subalpine fir grow in cool, moist habitats at lower elevations where wildfires are infrequent. Aspen also has thin bark and low tolerance to fire but it readily regenerates by sprouting. Aspen clones are connected by a network of roots which survive even very hot fires because they are insulated underground. Although the above-ground stems are killed by fire the roots send up a profusion of sprouts in the following years. Fire ecologists use estimates of fire return intervals to
better understand the role of fire in different forest types. Fire return intervals
represent the average frequency of fire for an area or plant community type on the
landscape. Natural, historical fire return intervals in Yellowstone range from 20-25 years
for shrub and grasslands in the Northern Range (Houston 1973) to 300 years or more for
lodgepole pine forests on the central plateau (Romme 1982, Romme and Despain 1989) and
subalpine whitebark pine stands. Romme, W.H. 1982. Fire and landscape diversity in subalpine forests of Yellowstone National Park. Ecological Monographs 52(2): 199-221. Romme, W.H. and D.G. Despain. 1989. Historical perspective on the Yellowstone Fires of 1988. Bioscience 39(10): 696-699. |
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Last modified: October 21, 2000
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EDITOR'S NOTE: This was the latest fire update for the 2000 season.
As of October 1, the fire season has ended. Early, heavy snows on the weekend
of September 22 effectively brought an end to the fires of 2000 in Montana, Wyoming and
Yellowstone. The photo to the left was taken in the Bitterroot Valley on August 6 by
John McColgan of Fairbanks, Alaska. This picture captures the essence of the 2000
wildfires.
The
history of wildfire in Yellowstone is long and varied. Even before written records of fire
with the advent of Yellowstone National Park in 1872 we see evidence of fire in soil
profiles, lake sediments, land slides, and in old-growth trees that have been scarred by
fire. It is clear that wildfire has had a role in the dynamics of Yellowstone’s
ecosystems for thousands of years.