THE BIOGEOGRAPHY OF WILDFIRES:
THE TILLAMOOK BURNS AS EXAMPLES
Brian L. Altonen
- Introduction 2
- Wildfire History 3
- The Evolution of Fire-Dependent Regions 6
- Fire Adaptations 8
- Wildfire Biogeography and Fuel 11
- Wildfire Biogeography and Winds 14
- Wildfire Biogeography and Water 16
- Geography and Wildfire 21
- Computer Mapping: the Geographer’s Role 24
- Conclusion 26
- Bibliography 32
TABLE I. PACIFIC NORTHWEST WILDFIRES FIRE SCHEDULE
- 1871 Peshtigo Fire, Wisconsin
- 1885 Adirondack Reserve Fire, New York.
- 1886 Yellowstone Fire
- 1894 Hinkley, Mn. Fire
- 1905 Forest Reserves Fire
- 1910 Rocky Mountains Fire
- 1933 First Tillamook Burn
- 1937 August 21 Blackwater Fire on the Shoshone
- 1939 Second Tillamook Burn
- 1945 Third Tillamook Burn
- 1947 Bar Harbor, Maine
- 1951 Fourth Tillamook Burn
- 1965 Centerville, Maine
- 1968 Oregon Weigh-Station Fire
- 1969 Oregon Bull Springs Fire
- 1977 California
- 1977 Alaska
- 1977 New Jersey Pine Barrens, July 22. 32,000 A.
- 1987 Silver Fire, Southwest Oregon, 53M#/58 days of inhalable/respirable particulate produced.
Fires are a recurrence in environmental history [see Table I]. Considered natural to the local ecology, they are produced by lightning storms, spontaneous combustion, and human-related pyrogenic events. The possibility that a fire initiates naturally, and becomes a major forest fire is increased during periods of drought. A typical forest fire is propagated by the biomass of the grasslands and woodlands where it begins, Both of these features are what typically limits the spread of fire whenever they define a significant portion of fuel source for a fire (Van Gelder 1976) [see Tables II and III]. In addition, a number of regions with a recurring history of wildfire have climatic variations, local landforms, and natural history which play key roles in local fire ecology. In sum, the biogeography of heavily forested regions susceptible to wildfire is defined by the available fuel sources in combination with natural methods of ignition and propagation of fire that a regions has, to which is often added the ecologic impacts of other natural events which occur due to these fires, natural events that to some extent are self-sustaining for the particular ecosystem being impacted (Agee 1990; Kauffman, 1990).
TABLE II. WILDFIRE BIOGEOGRAPHICAL REGIONS
I. Conifer-rich Boreal Forests
A. Pseudotsuga menziessi (Douglas Fir) dominant
B. Pinus ponderosa dominant
II. Mixed Conifer-Deciduous Middle-Latitude Forests
A. Pinus-Quercus dominant
III. Deciduous Forests (Southern Hemisphere)
A. Eucalyptus dominant
IV. Mediterranean communities
A. Chapparal dominant
The events which turn natural fires into devastating wildfires are quite different from those responsible for the typical self-limited forest fire. Unlike periodic, small scale forest fires, wildfires do not really serve much of an ecological other than to clear away the large amounts of debris and detritus that helped to sustain these events once the initial ignition phase is over. Whereas wildfires result from natural events similar to those of the forest fire, unlike forest fires, they consume a great deal more acreage, usually 10,000 acres or more. Most of the time, the actual events that lead to wildfire ignition are typically of human origin, and usually take place as the result of some form of human activity or behavior, deliberate or not. The changes in local ecology which follow a wildfire make the burned over regions less likely to undergo a full environmental recovery, and often lead to an instability in the landmasses situated beneath the burned areas. The ultimate outcome of such events is usually ongoing in nature, resulting in many predictable outcomes also very disaster-like in nature, but also events that often wind up being unpredictable, unexpected, and unwanted. In sum, the ignition, propagation, and ecologic impact of wildfire is determined by human biogeography, not natural history.
TABLE III. PYROGENIC PLANTS
Source: Hefner and Deeming 1978.
Grasses: western annuals, perennial, saw grass.
Savannah: open timber and grass regions
Brush: sage, high pocosin, mature amd intermediate chapparal, southern rough palmetto-gallberry regions.
Timber: short-needled conifers-heavy and normal dead; long-needles conifers-normal dead, southern pine plantations, Alaska Upland Black Spruce regions, Hardwoods.
Wildfires require three factors for ignition. They need a heat or flame source such as lightning, a dry fuel source such as trees and shrubs, and weather conditions capable of supporting ignition, propagation, and rapid spread. Wildfires also need a continuous oxygen source, typically provided for by nature in the form of strong surface winds and convection currents. In turn, the relation of each of these factors to local landforms, the presence of dry conditions on land and in the air, and most importantly, the presence of a highly flammable fuel source for ignition and a dense fuel source for wildfire propagation, are the natural events most responsible for the increased number of wildfires in recent years (Pyne, 1984).
Recent wildfires in North America have consumed massive amounts of economically-important rich conifer and mixed conifer-deciduous (usually oak-bearing) forests (Cleaves and Brodie, 1990, pp. 277, 280, Pyne 1995). Even though these ignitions depend on regional climatic, ecological and meteorologic events, and various forms of direct and indirect human activity to give rise to their ignition, this human biogeography of wildfires is not new and can be used to explain the historically important wildfires of the Midwest during the late 1800s and early 1900s.
As soon as industrialization took place in the Midwest and Rocky Mountains, many regions became increasingly susceptible to fire. The impacts of deforestation and conservation, along with human activities, led to the propagation and spread of three wildfire events in the Northern-Midwest during the late nineteenth century, (Haines and Sando, 1969; Pyne 1995). The Peshtigo Fire of 1871 for example occurred as the direct result of the rapid migration in settlers into this region just several decades earlier. These migrations in turn led to the passage of laws designed to prevent the harvesting of valuable timber, after which the development of large amounts of undergrowth ensued, followed by their ignition in Summer of 1871 (Wells 1968; House, 1992).
In 1885, a wildfire took place in the Adirondack Reserve of New York. The following year a similar event took place in the newly established Yellowstone Park. Then, in 1894, wildfire consumed one of the nation’s most economically important conifer forests near the lumber town of Hinkley, Minnesota. This and the subsequent Forest Reserves wildfire of 1905 had tragic effects on regional and local economies. Following a similar wildfire event in the Rocky Mountains in 1910, the forestry service began developing plans for the prevention and elimination of both forest fire and wildfire history (House, 1992).
Soon after the Rocky Mountain fire, the West Coast also began to experience heavy migration, turning West Coast timber into an important resource for future development. This led to the practice of fire suppression in economically important Sequoia, Western Cedar, Western Hemlock, Sitka Spruce, and Douglas Fir forests through government protection. After only twenty-five years of this protection passed, the first major wildfire took place on the West Coast as the 1933 Tillamook Burn. As was the case for the conservation practices of Wisconsin, Minnesota, and Yellowstone Park, Tillamook forest reserves became overgrown. In the southwest, where the development of Mediterranean-like chapparal regions was taking place, numerous wildfires also developed due to the prevention and elimination of scrub-fires during the middle twentieth century.
Therefore, throughout the colonial years of the Atlantic Maritime region, the early post-colonial years of the first “Northwest” and Midwest, and the middle to late nineteenth century settlement years in the Midwest and Far West, fire suppression activities gave rise to the events which finally erupted at Peshtigo, Wisconsin in 1876. Following the supplanting and removal of Native American groups to reservations, these regions lacked the earlier cyclical fire activities practiced as preventive measures by Native American groups and the related grassland-forest environmental histories.
The Evolution of Fire-Dependent Regions
The natural selection for fire-dependency came about due to evolution. When conifers first developed, they resided in tropical regions where the greatest biodiversity existed. With the formation of the Angiosperms, the removal of less efficient conifers from the tropics and into the much cooler temperate and sub-arctic regions took place (Briggs, 1995, pp. 137-8, 176-7, 325-6). Similar events led to the growth in biodiversity of sub-montane regions, as conifers removed to the higher altitudes where cold temperate and sub-arctic climates persisted. This migration is also what led to the natural selection of conifers residing in colder, higher altitude regions, as later warming took place due to receding ice ages (Kussela 1992, 1992).
Some evidence suggests that the adaptations of conifers to wildfire first developed as adaptations to temperature extremes in global climatic history. Conifers probably developed their viscous resin to improve their tolerance to the extreme cold. Their thick bark on the other hand was designed to allay the threat of fire during warm, dry haplothermal periods. As similar development took place within the angiosperms, the future survivability of conifer species came to depend more upon their newer adaptations for dealing with recurring forest fires. Thus their ability to remove from rapidly growing angiosperm regions to the less active sub-arctic regions came due to much earlier climate-based evolutionary developments (Briggs, 1995, 176-7).
Accompanying the need for heat tolerance on behalf of conifers is drought tolerance. The fact that conifers ar capable of residing in both hot, arid, and cool, moist conditions suggests that theses behaviors evolved as pre-holocene traits to contend with the more drastic changes in temperature then taking place. We find current boreal and sub-boreal forests exemplify this role of natural history in conifer development. The fire-prone forests of Saskatchewan (Ogilvie 1989) and Ontario (Stocks 1977), which bear Jack Pine (Pinus banksiana Lamb.) and Balsam Fir (Abies balsamea (L.) Mill.) stands, developed these survival patterns for the same reason as the Scots Pine (Pinus silvestris) forests of Germany (Goldammer 1979), numerous Chinese and Russian forest, the former conifer-rich regions of Scandinavia, and the southernmost edge of Australia which harbors the resin-rich Eucalyptus.
In conclusion, plants dependent upon wildfire for their continued survival did not necessarily develop their pyrophilic or pyro-tolerant features due to the presence of fire during their evolution. Instead these features and adaptations to living habits underwent continuous change over the years, giving rise to the ecosystem which now exist that are dependent upon recurring fires for their continued propagation.
Recent studies of Mediterranean biogeography note the importance of fuel types in fire and the role of fire-dependent climax species in producing regions with recurring forest fire ecology schemes. Various pines, for example, provide the fuel needed for fire ignitions, such as duff, needles and cones. In turn, these pines depend on fire to disperse their seeds from resin-sealed cones and clear the land for re-seedings to take place. Examples of these serotinous conifers include Aleppo pine (Pinus halepensis), Stone pine (P. pinea), Maritime pine (P. pinaster), Corsican pine (P. nigra), and Brutia pine (P. brutia) of the Mediterranean region in Europe (Velez, 1990a), the Monterey and Bishop pines of California, and the Lodgepole pine (Pinus contorta), Sugar pine (Pinus lambertiana) and Ponderosa pine (Pinus ponderosa) of the Pacific Northwest. Similar attributes are shared as well by many other conifers, including Douglas Fir (Pseudotsuga menziesii), Incense Cedar (Libocedrus decurrens), and various Junipers (Juniperus spp.) (Kauffman, 1990, pp. 46-47). Together these Pinus features suggest a regional-climatic link in their evolution and propagation. All are of a maritime nature, many residing on raised lands away from the locally-humid maritime weather, but not out of reach of the forceful maritime winds.
In the Pacific Northwest, adaptations to this weather-fire relationship are borne by such conifers as Western Larch (Larix occidentalis), Ponderosa Pine, Douglas Fir, Grand Fir, and Western White Pine (Pinus monticola), which are listed in descending order of fire resistance (Franklin and Dyrness, 1973, p. 192). In addition, other adaptations to fire-prone regions are noted, for example, Larch rapidly replants following a fire due to the delivery of its lightweight winged-seeds by wind. Certain oaks have lateral buds which are activated by the removal of terminal and lateral buds due to fire. Many sclerophyllic broad-leaved evergreen plants, like Arctostaphylos uva-ursi, Mahonia aquifolium, and various Berberis species, re-grow from root stock so long as high ground temperatures have not been reached during a burn. Finally, many conifers survive fire due to its impact on diseased members, the elimination of disease-causing agents (such as insects and Mistletoe (Viscum spp.) and the removal of overactive herbivore populations (Thies, 1990). The Ponderosa Pine, for example, uses fire as a natural defense against western pine, pine engraver, and red turpentine beetles (Mitchell, 1990, p. 113-114; Flanagan 1996); during its recovery, its rapid regrowth may be facilitated and the branching improved due to browsing branch tip-consuming deer.
Other fire-survivors such as Lodgepole and Whitebark Pine are noted to have low fire resistance, but yet require fire for seed replacement. Poor tolerance to fires is seen with hemlocks, certain larches, firs, spruce, and cedars. Douglas Fir is most susceptible to fire-related injury and death during its young to middle years (i.e. less than 200 years old), which is in part due to its moderate bark thickness. Since potential scorch height also plays a role in defining the Douglas Fir’s reaction to fire, the lower crown base containing highly flammable dead branches may serve in wildfire propagation and crown scorching. Yet, even after crown scorching has taken place, deep-rooted conifers oftenm remain uneffected by fire. Such a trait of Douglas Fir once again suggests it re-adapted to live in a cool temperate region, following its removal from a sub-arctic climate and post-glacial warming.
Wildfire Biogeography and Fuel
Wildfire is distinct from the smaller, seasonal forest fires which most trees adapt to. Whereas periodic fires are rapid burning and self-extinguishing, wildfires go through two major burning stages. The initial stage of wildfire is the aggressive burn of both the understory and canopy, during which the wildfire often explodes into being, is short-lived, and is of minimal destruction to major trees and the forest floor. The second stage of a wildfire burns hotter, longer, and is more capable of producing long-term destructive effects on forest life and wood products. It makes use of the embers being produced as part of a much more complete combustion process and ash production process that ultimately extinguishes the various lifeforms residing on and within the forest floor (Pyne, 1984, pp. 17-25).
Once a fire begins to carry out its rapid burning and flame production as its first stage, it consumes mostly the highly-flammable fuels such as resins, essential oils, seed oils, and lipids. These fuels undergo rapid incineration, evaporation, and incomplete combustion or pyrolysis. The pyrolytic stage of the burn releases various complex chemicals into the atmosphere as debris, aerosols, and evaporants. The deposit of the remaining unburnt fuel and tar-like substances onto the forest floor then follows. These rapid-burning processes take place not only on the surface of the floor, but also within the forest’s understory and its canopy (Pyne, 1984, pp. 27-29). The brevity of these fires causes little destruction of the total biomass, and adds important nutrients to the soil (Miller and Seidel, 1990; McNabb and Cromack, 1990). Should this fire continue and then start to comsume wood-rich materials like dead branches and duff, then high temperatures are reached near the floor and initiates the second stage of the burn.
The formation of glowing embers behind the front line of a fire results from the second stage of a wildfire. It often involves the complete conversion of lignin and other fuel sources into carbon dioxide and water by means of a complete combustion process. The ash which remains is the end-product (Pyne, 1984, pp. 27-29).
During combustion, temperatures along burning sites become more damaging to the remaining lifeforms which reside there. This stage in the burn is what differentiates wildfires from common forest fires, for it usually reverts regions of a semi-pristine to modified state to a barren state with floral patterns that are more like those of the earliest stages in plant succession for that region. Equally important is the impact this stage in a wildfire has on soil chemistry. It can modify and sterilize any remaining biota left behind, which traditionally was previously untouched by much smaller forest fires (Pyne 1984, p. 7; Borchers and Perry, 1990, p. 151).
These changes in ecology due to wildfire are the results of local weather, landform, and plant geography patterns. Droughts prepare the forest floor and canopy for rapid burning. Ignition is required to start the fire. Dry winds help feed it and allow wildfire to continue. These fire-directing features are the direct result of landform features and water behaviors for the given region. Therefore, wildfires are often seen in close association with hillsides which bear significant slopes and windward faces, where dry weather, winds, and landform then combine with local plant patterns to form a local biogeography highly susceptible to ecological forest fires and at times wildfires.
A study of the Pocosins illustrates the two major fuel types needed for wildfires. The Pocosins depend on three to four year fire cycles to remain stable. In 1972, following the prevention of these fire cycles during previous decades, more than 10,000 acres burned. The recovery, growth, and rejuvenation of Ponderosa Pine (Pinus serotine Michx.) which ensued was matched by a recovery of Lowbush Gallberry (Ilex glabra (L.) Gray, an evergreen that holds it foliage over the winter, and Gamble Oak (Quercus gambelii Nutt.). Both survived after serving as the major hot-burning fuel sources for this region (McNab et al., 1979).
This mixed deciduous-conifer combination for a fire-dependent forest not only illustrates the important roles played by two types of chemical components in shrubs and trees–resin rich pine and lignin-rich oak–it also illustrates how each of these fuel types have adapted to fire-prone regions. Each plant plays a different role in the stages of natural pyrogensis. The resin is responsible for ignition and spread. The conversion of brief fires into long-term burns takes place due to hot-burning oaks (McNab et al., 1979).
Studies of the Midwest Sub-Montane and Eastern Maritime regions also show that these fire-prone regions are composed mostly of pine and oak fuel sources (Brotak and Reifsnyder, 1977). As subsequent research further supported this finding, it also illustrated how evergreen sclerophyllous deciduous trees can adapt to forest fires by producing a thick bark to serve as insulation and a much denser hardwood which is slow to ignite. In the Mediterranean for example, trees bearing these traits include Holm Oak (Quercus ilex), Cork Oak (Q. suber), and Quercus coccifera, the last of which bears dormant buds in large numbers capable of opening following fires (Velez, 1990a). In the Pacific Northwest, where oaks are less dominant in wildfire regions, the hot-burning fuel sources are the much smaller evergreen sclerophyllous shrubs like Salal (Gaultheria shallon) (Franklin and Dyrness, 1973, pp. 73, 132-3).
Wildfire Biogeography and Winds
The second biogeographic element for fire–air in the form of foehns–has received blame for many maritime zone wildfires, especially in the Pacific Northwest. Velez noted many wildfire-prone regions develop periodic, strong, desiccating winds such as the tramontane in Catalonia and Italy, the mistral in the Rhine Valley, the khamsin in Lebanon and Syrian Arab Republic, the sharav in Israel, the sirocco in Maghreb, the poniente in Valencia, and the levanter in the Strait of Gibralter (Velez 1990a). These winds are easterlies known as Santa Ana winds in California, and the easterly winds (sometimes Chinook winds) in Oregon, both of which are foehns (Pyne 1995).
In the case of Chapparal fires, such weather conditions as prolonged summers (i.e. lasting from June to October), drought conditions, daytime temperatures of well over 30 degrees C., humidity below 30%, and high winds to spread the sparks, are responsible for the propagation of these fires following their initiation due to natural or human-induced events. The local foehn winds common to parts of Southern California are also responsible for the recurring history of these fires. Whereas topography, slope, wind, and weather help to produce these Chapparal fires, the biomass of this region still remains responsible for much of its long term history. Low-lying stunted trees and shrubs responsible for these rapid burns include chamise (Adenostoma fasciculatum) (90% of biomass, or one-third of the cover), scrub oak (Quercus dumosa), California sage (Artemisia california), manzanita (Arbutus menziesii), sumac (Rhus spp.), and buckthorn (Rhamnus californica) (Klinger and Milson, 1968). The biogeography which is blamed for these fires produced these complex fuel sources (of more than one species), and the local air circulation patterns needed (Brotak, 1977; Brotak, 1992-1993, p. 26).
In Oregon, the conditions which give birth to such fires (i.e. the Tillamook burns) are reversed. Oregon wildfires depend on a single type of fuel source–conifers–rather than a mixture of hot burning deciduous trees with resin-bearers. Like the Chapparal fires, Oregon’s fires can be supported by strong east winds, but in addition, as these winds react to the steep inclines of the coastal range, they produce unique weather conditions known as dry-storms. These are the events which gave rise to the Tillamook wildfire of 1933 (Dague, 1936; Gray, 1936).
Wildfire Biogeography and Water
The first significant study of the meteorological-biogeographical causes for wildfire was carried out in 1951 for the Department of Forestry by George M. Byram and Ralph M. Nelson (Byram and Nelson 1951; Byram 1954). Byram defined a method for predicting the impacts of drought as precursors to wildfire. This ultimately led to the creation of Byram’s Drought Index, a measurement still in use for ecosystem-wildfire management.
By the 1960s, a better understanding of midwest forest fires clarified the natural causes for pyrogenesis. One researcher proposed that fires in mountains tend to occur due to the order in which the sun strikes mountain slopes (Countryman 1966). This rule however did not hold true for fires like the Tillamook burn, which experienced an early morning ignitions due to low-intensity burns which burned overnight and then re-ignited with the early morning winds and increased early morning solar drying. Therefore, by the middle 1970s, speculation about the natural ignition of fires began to focus more on natural causes inherent to forest biogeography and ecology.
In 1973, Robert Matthews blamed some of the fires on the “Punky wood or heavy duff…[which] catches and holds sparks” in the forest floor (Matthews 1973). Several years later, Donald Haines of the Forestry Service proposed his theory that unique lightning storm patterns were responsible for drought-related wildfires (Haines et al. 1976). Haines argued that during periods of severe drought and atmospheric dryness, precipitation fails to reach the terrain even though lightning can continue to reach the ground. Haines then used his theory to explain 50% of the fires in Montana, Idaho, Arizona, and New Mexico, and 45% of the fires in Oregon (Main and Haines, 1976).
Most important to Haines’s theory was the association he made between geomorphology, weather, and ignition potentials. Haines suggested that landforms responsible for dry thunderstorms also led to the formation of lightning responsible for dry ground ignition. Haines noted that whereever cloud bases were set high above the terrain, the rain fall evaporated on its way to the ground as the same region underwent intense lightning strikes. Known as “High Level Dry Thunderstorms,” Haines concluded that this geomorphology-meteorological feature was responsible for fires in the western mountain ranges like the Tillamook burns (Maine and Haines, 1976, p. 6).
Haines’s study set the stage for a more complete review of the physical geography study of wildfire carried out by Edward A. Brotak of Yale University as his Dissertation topic in 1977 (Brotak 1977). Brotak concluded that certain landform features in the midwest assisted the ignition of wildfires and their continuation. The features produced were the onset of drought and aridity, lightning storms and human activities, and the initiation of fire-supporting windflow patterns, all of which are climatic patterns needed for wildfire ignition.
Haines’s and Brotak’s events can be related to regions along the Atlantic and Pacific Coasts at climatic borders inland from the maritime regions. As examples, consider the the mixed conifer-deciduous Pine Barren forests of Long Island, New York, parts of New Jersey, and South Carolina (Green, 1990; Richards, 1990). The Pacific Northwest Western Hemlock and Douglas Fir Zones bear mostly coniferous biomass to fuel a fire, as well as a small understory of hot-burning but very small ligneous shrubs (i.e. Salal) and ferns (Franklin and Dyrness, 1973, pp. 72,85-89). The Siskiyou Mixed Deciduous-Mixed Evergreen regions bear a mixed decidiuous-evergreen fuel source (Franklin and Dyrness, 1973, p. 133). Similar maritime regions with rich fire histories include Alaska (Anonymous 1977; Heinselmann, 1971), Indonesia (Cougill, 1989), Turkey (Ozyigit and Wilson, 1976), the Heilongjiang Province Northern China (Salisbury, 1989), India (Saigal, 1990), and even the high altitude conifer forests of Guatemala (Veblen, 1978; Dembner, 1990/3).
Following his post-doctoral research, Brotak used his findings to support his claim for the forest fire and wildfire events which took place in the New Jersey Pine Barrens. This region consisted of a mixed deciduous (mostly Quercus)-Conifer (Pinus sp.) community, under the influence of Maritime weather patterns augmented by lightning. The July 22, 1977 wildfire which took 32,000 acres of these Pine Barrens illustrated how meteorological events cause massive wildfires to develop (Brotak, 1978-9).
For the New Jersey fire, Brotak concluded that a Cold Front originating from a High Pressure system over the Great Lakes and an attached trough which helped form winds originating from the North-Northwest gave way to an influx of warm air and a drop in the humidity of the Pine Barrens. This setting resulted in the ignition of a forest fire fed by a convection column consisting of constant winds at speeds greater than 10 mph. Brotak has since compiled a fairly precise method of determining the likelihood of ignition, propagation, and spread of these wildfires using Low-Atmosphere Severity Index, Vertical Temperature structure and Lapse Rate (which influence convection over the fire), and amount of air moisture present capable of adding moisture to possible fire fuels (Brotak 1978-79).
Proof of Haines’s and Brotak’s protocols for predicting wildfires came most recently as the Rocky Mountain and Pacific Coast fires (Beighley and Bishop, 1990). The “High Level Dry Thunderstorms” noted by Haines were formed by lightning strikes to dry ground, in turn leading to natural pyrogenesis and the formation of a convection column above (Main and Haines, 1976, p. 6). This convection, in turn, was assisted by surface winds blowing just above the canopy and the slower winds which blowing aloft. These high elevation fires were noted to respond favorably to light winds, usually less than 25 miles per hour. After confirming his proposed causes for Western United States conifer wildfires, Brotak concluded that a review of 700-500 mb temperature differences at High Elevations, the 700 mb dewpoint depression, and the surface to 500 mb wind profile are needed to determine if changes taking place in nocturnal inversion pattern behaviors between late morning and mid-day can in turn cause unstable fire conditions and “blow-up” (early morning ignitions) to take place (Brotak, 1992-1993, p. 26).
Following “blow-up,” the presence of the convection pattern overhead becomes very important in the continuation of Pacific Northwest wildfires. Unlike East Coast fires, which involve low-altitude flat to hilly conifer- and oak-rich forests, West Coast fires involve higher altitude, sloping lands capable of producing strong winds which are funneled into conifer forests by landforms. This leads to rapid ignition, blow-up, and propagation and spread of wildfire. These fires are also dependent upon monthly meteorological patterns, about two-thirds of them take place in June and August, periods when atmospheric instability, convection, strong surface winds, and drought conditions can often set in. These seasonal conditions occur in both eastern and western maritime regions, and are similar if not identical to the conditions which gave birth to the Tillamook burn in 1933, as well as Tillmook’s subsequent fires in 1939, 1945, and 1951 (Dague, 1936; Brenner, 1991).
Geography and Wildfire
The role of geography in wildfire studies has several applications. Since similar wildfire events take place in many regions around the world, geographical computer mapping provides methods for facilitiating the prediction of wildfires (Rechel, 1992-3; McCuthan et al., 1995). In China for example, the potential for wildfire was studied and show to have causative factors similar to those of the Pacific Northwest and parts of the Midwest: winds ranging from 27 to 43 mph., hilly terrain and mountains, slopes less than 15 degrees, and numerous rivers which provided shallow beds and open grasslands to help the fire spread (Westoby, 1975; Fuchs, 1988). The association of wildfire with particular latitudes has been noted by the Chinese and several European researchers (Salisbury, 1989; Pyne, 1995).
The use of geography to better understand regional forest fire patterns also provides support for the recent revival in the practice of prescribed burns. Traditional Native American practices have historically involved the periodic burning of local ecosystems. Their goal, according to historians, was to facilitate the use of lands for exploration, settlement, and travel and to improve hunting and foraging. Important plants influenced by these periodic burns include Blueberry and Wild Huckleberry as important food sources (Minore 1972; Kautz, 1987), Hazel (Corylus cornuta var, californica) for nut and wood products, and Beargrass (Xerophyllum tenax) for fiber production (Hunter, 1988).
To both the biologist and the forester, the fire prevention goals prior to 1930 were directed toward suppressing both the first and second stages of the burning process [see Table IV]. This led to massive growth of understories which in turn served as an important fuel source in any fires capable of reaching their second stage. On September 20, 1937, for example, a Shoshone Blackwater Fire on August 21 was blamed on the “scrubby jungle look” of otherwise “low-danger forest conditions” within a Lodgepole Pine-Fir community (Granger 1937). During this same decade, numerous fire hazards began developing around unattended railways due to the growth of lush vegetation near the tracks (Gustafson, 1937a, 1937b).
Similarly, the active prevention of scrub-fires in California in recent years enabled the growth of normally fire-resistant Ceanothus shrubs to take place (Klinger and Milson, 1968; Philpot, 1974; Leisz, 1977; Radtke, 1982). As Ceanothus reached twenty-five to thirty years of age, this led to a collection of dead branches at the base of their crowns, changing these shrubs from a state of low-flammability to high-flammability. Most recently, these same conditions are what led to a major wildfire in 1990 during an extreme drought condition (Meehan 1991).
During the 1960s, fire prevention measures were taken through the use of herbicides and the allowance of understory grazing (Corlett, 1967; Cowles, 1972). By 1970, this was followed by the initiation of prescribed burns tests on the Apache National Forest (Buck 1970-1), and the Bitterroot Mountains, Missoula, Montana (Anonymous, 1971; Aldrich and Mutch, 1971-72). Due to these tests, Stephen Arno published his findings on the importance of forest fire in 1978. Arno noted that different fire histories exist with Douglas Fir/Western Larch, Lodgepole Pine/Engelwood Spruce, and Subalpine Fir/Whitebark Pine stands due to the different ecologies borne by each of these regions (Arno, 1978).
Arno’s study showed that by allowing the removal of undergrowth and even crown burning to take place, fire ecologists allow a new form of natural stabilization to take place which should lessen the future risk of wildfire (Arno, 1978). Most recently, nearly twenty years later, important steps were taken by administrators in Washington, D.C. when Bruce Babbitt recommended a return to periodic burning of one-hundred fifty years previous, prescribing periodic burns to large forest reserves every several years (Babbitt, 1995).
Computer Mapping: the Geographer’s Role
Fire prediction measures are applied to computer mapping in two ways: through the use of Fire Indices, and for the planning and control of future forest harvests and growth (Hirsch, 1989). The use of the Keetch/Byram Drought Index [KBDI], a method of analysis designed in 1968 and revised in 1988, is currently undergoing a revitalization due to its potential computer applications. Used to determine the depth of drought-derived impacts on the forest floor, it determines through mapping the relative saturation of soil which in turn reflects any potential use of roots as ladder fuels by propagating fires (Melton 1989; Melton 1996). Another measurement applicable to computer mapping is fire vulnerability based on geographical and ecological patterns as each relates to fuel sources, topography, weather, low-atmospheric Stability Index (high index = stability and moist), and the presence or absence of certain regional weather patterns (i.e. the Santa Ana and Sundowner winds) (Andrews and Chase, 1990; Werth and Ochoa, 1990, p. 10-11).
These projects have subsequently been improved by the most recent use of satellite monitoring devices, along with the support of the Federal Emergency Management Agency [FEMA]. FEMA has involved itself in this ever-growing human ecology problem by analyzing the effects of climate and ecology on large fire-production processes, and by supporting the development of a Geographic Information System known as METAFIRE in which specific data concerning latitude-longitude, time zone, elevation, primary and secondary fuel sources, climatic region/class/normalization, Palmer Drought Index, Current Soil moisture data, and Keetch Spring and Fall Codes for detecting major changes in season are recorded (Simard and Eeningenburg, 1990; Eenigenburg and Main 1995).
In recent years, the value of the geographer in this field has been in the development of “spot forecasting” skills. The 1994 Storm King fire was “spot Forecasted” based on cloud observations, inversion breaks in the morning, general windshifts (upslope vs. downslope, and up versus down valleys), smoke dispersal rates, and instability indicators including dust devils and towering cumulus and cumulonimbus clouds. Additional factors assisting in this forecast included low temperature and high humidity in the mornings around 1 to 8 AM, which changed to high temperature and low humidity by 2 to 3 PM due to strong diurnal wind patterns (Cuoco and Barnett, 1996).
During the 1880s, ranchers who lived in the fire-prone regions of the Western United States indirectly began to suppress wild fire activities. The animals which they raised grazed on the undergrowth in the local forests, removing part of the debris required for periodic brush fires to occur in this region. In addition, due to the Rocky Mountain wildfire in 1910, concerns grew about the need to preserve a valuable timber source, a public attitude reached its peak during the first World War when western evergreens like Sitka Spruce, Port Orford Cedar, and Douglas Fir became important sources for the natural materials needed to manufacture aircraft and ships (Babbitt 1995).
The purpose of researching natural pyrogenesis and wildfires in two-fold. First, it leads to a better understanding of the forest as an ecosystem. Secondly, it has served as an important component of human geography research made by future land use planners (Fahnestock, 1971; Lynch, 1974; Williams, 1995). Whereas some of those who research forest fires hope this will result in improvements in the silviculture industries by the prevention of wildfire through better silviculture management (Van Gelder, 1976; Velez 1990b), others view this understanding of both fire and wildfire to be important to our understanding of past and the modern global environment and its future ecology (Alexander and Andrews, 1989; Shugart and Smith 1992).
Since fire and its progenitor, heat, are important to life and climate, serving as energy natural sources for biota, perhaps the best interpretation of fire begins with the assumption that it exists for one or more reasons. The best natural conception of fire begins with understanding it as an important part of past, present and future global survival. Thereafter, fire prevention and unnatural propagation can be judged either as the result of failures of natural ecology, or as measures of success in human ecology.
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