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QUATERNARY RESEARCH 3, 408424 (1973)

Fire-Dependent Forests in the Northern Rocky Mountains

JAMES R. HABECK~ AND ROBERT W. MUTCH~

Received April 15, 1973

One objective of wilderness and parkland fire-ecology research is to describe the relationships between fire and unmanaged ecosystems, so that strategies can be determined that will provide a more nearly natural incidence of fire. More than 50 yr of efforts directed toward exclusion of wildland fires in the Northern Rocky Mountains (western Montana and northern Idaho) have resulted in a definite and observable impact on the forest ecosystems in this region. Fire-ecology investigations in Glacier National Park and the Selway-Bitterroot Wilderness have helped to reveal the nature of this impact and to provide a better understanding of the natural role of fire within these coniferous ecosystems. Such areas provide a unique opportunity to study and test approaches designed to perpetuate unmodified ecosystems. However, we still don’t understand all of the long-term consequences of fire control in those forest communities that have evolved fire-dependent characteristics.

INTRODUCTION

Large areas have been established as national parks and wildernesses in the North- ern Rocky Mountains. Their management calls for the perpetuation of all natural forest ecosystems, including those that are fire-dependent. However, these areas have received the same degree of fire suppression that is achieved in commercial forests. There is a renewed interest in the ecology of fire-dependent species, because exclusion of wildland fires may have detrimental side effects (Heinselman, 1970; Dodge, 1972; Kilgore, 1972 ; Kilgore and Briggs, 1972). This concern is supported by an application of basic ecological theory. Many kinds of habitat alterations that cause prolonged or permanent modifications of site characteristics (e.g., changes in soil moisture or nutrient supply) will predictably lead to sig-

’ Department of Botany, University of Mon- tana, Missoula, Montana 59801.

BUSDA Forest Service, Northern Forest Fire Laboratory, haissoula, Montana 59801,

nificant changes in community structure and function. The effective reduction of fire cn landscapes that historically were influenced by periodic fires will have a modify- ing influence that is detectable and measurable (Fig. 1).

Fire-dependent forest ecosystems require fire treatment for their continued perpetuation on the landscape. The competitive success of fire-dependent species is directly related to the selection of characteristics that improve the fitness of populations in the fire environment of the Northern Rocky Mountains. Many species here exhibit morphological and physiological adaptations that provide survival advantages on landscapes that are subjected to fire cycles. We suspect that the diversity of community life forms engendered some sort of ecosystem equilibrium or a kind of biologic “checks and balances” system that governed the magnitude of the effects accompanying a given forest fire.

Personnel from the USDA Forest Service and the University of Montana are seeking

408

Conyright c 1973 by University of Washington. All rights o P reproduction in any form remrvad.

FIRE-DEPENDEET FORESTS, SORTHERN ROCKIES 409

FIG. 1. Tango Cr& Fire, 1953, Bob Marshall Kiidwnes, blontonu

to gain understanding of the extent to which fire suppression in the Northern Rocky Mountains has modified coniferous ecosystems. Without such investigations we will not fulfill the management objectves for national parks and wildernesses. Any management prescription designed to insure a return as closely as possible to a natural incidence of fire on these landscapes must be built upon sound field data. Up to this time both research and administrative studies have been investigating fire-dependent ecosystems in the Selway-Bitterroot Wilderness and in Glacier National Park.

The purposes of this paper are to describe the vegetation patterns shaped by the fire environment of the Northern Rocky Moun- tains, to relate fire-dependent species to ecosystem stability, and to discuss the practical application of such knowledge to wilderness fire management.

GENERAL CHARACTERISTICS OF THE NCRTHERN ROCKY

JIGI-NTAINS

The Northern Rocky Mountains are com- posed of a series of mountain ranges that average between 2400-3100 m (7874-10,170 ft). These ranges are generally orient,ed in a northwest to southeast direction; many are separated by well-defined intermontane valleys occurring at 800-1100 m (2625- 3609 ft) above sea level. The drainage pattern for the entire region is complex; the ranges west of the Continental Divide are drained by the Columbia River system, and those on the cast side by the Missouri River system.

A large portion of the Northern Rocky Mountains was glaciated during the Pleis- tocene, either by the Cordilleran or Conti- nental ice sheets from Canada, or by local

410 HABECK AND MUTCH

mountain glaciers. Many large freshwater lakes in western Montana and northern Idaho were formed by past glacial action. A large portion of this region was inun- dated by Glacial Lake Missoula, and the features of many of the valleys in western Montana have been modified by this past water influence.

Much of the Northern Rocky Mountains west of the Continental Divide is influenced by a Pacific coastal climatic regime. Mois- ture-laden air masses from the northern Pacific Ocean sweep along easterly moving storm tracks at this latitude. Although moisture is lost as the air masses move over the Coastal and Cascade Mountains, much moisture is retained and carried farther eastward into the Northern Rocky Moun- tains. At the higher elevations, annual pre- cipitation may be 1500 mm (59 in.) or more, much of which is in the form of win- ter and early spring snowfall. The intermontane valleys, in contrast, typically re- ceive 380 mm (15 in.) or less annually.

Of particular importance in the annual climatic regime is the marked reduction of moisture during the midsummer months. Many weather stations in western Montana and northern Idaho report 24 mm (1 in.) or less rainfall during July and August. This reduction in moisture allows consider- able desiccation of forest fuels during the warmest months of the year. Summer lightning storms, combined with the drying forest fuels, set the stage for wildfire ignitions.

As a result of the Pacific coast climatic regime, the vegetation of the Northern Rocky Mounta,ins is closely related to that found along the Pacific coast. Western redcedar (Thuja plicata) , western hemlock (Tsuga heterophylla) , western yew (Taxus brevifolia) , western white pine (PiWUS monticola), and grand fir (Abies grandis) are good examples of species whose main botanical ranges lie farther to the west. Dozens of shrubs and herbaceous species also display similar eastward range exten- sions from western Oregon and Washington. In the distant past, all of these species were

more widely distributed in the Northern Rocky Mountains. However, following the upthrust of the northern Cascade Moun- tains, ranges of these species have become limited because of decreased moisture con- tent. This shrinkage of ranges has con- tributed to the complexity of vegetation, particularly in western Montana.

AN OVERVIEW OF FIRE- DEPENDENT FORESTS IN THE

ROCKY MOUNTAINS

Both authors have had over a decade of field experience with forest vegetation and fuels in the Northern Rocky Mountains. The senior author has been engaged in a continuing phytosociological analysis of grassland, forest, timberline, and alpine communities in this region; the junior author has had comparable experience in the study of forest fuels in many different forest ecosystems. During their field work, direct evidence could usually be found that past fires had influenced most plant communities. The presence of charcoal, either above ground or in the soil profile, has indi- cated that most areas have been burned.

Anyone knowing forest successional patterns and species relationships can readily observe that a high percentage of the vegetation, within all forest zones, is at one stage or another of succession following past fires. Climax, or near-climax, forest stands that have escaped fire for several centuries are only rarely found in northern Idaho and western Montana. It is believed that past, uncontrolled fires did not, at any one point in time, create a completely burned over and denuded landscape, because many stages of successional development can usually be found in each forest zone.

Written historical descriptions of the region’s plant communities predate the effects of modern fire-control measures. Two of the best early descriptions of the effects of fire on Northern Rocky Mountain forest vegetation are the reports prepared by Leiberg (1900) and Ayres (1900). Leiberg reported

FIRE-DEPENDENT FORESTS, NORTHERN ROCKIES 411

on the forest resources within the original Bitterroot Forest Reserve. Ayres prepared a similar report for the Flathead Forest Re- serve. The boundaries of the Selway-Bitter- root Wilderness are well within the area discussed by Leiberg, and those of Glacier National Park are within the forest reserve described by Ayres. Both emphasized the nature and extent of recently burned-over forest lands. Over the past 70 yr, our under- standings of forest succession and the dependency of certain tree species on periodic fire treatment have expanded manyfold.

FOREST ZONES OF THE NORTHERN ROCKY MOUNTAINS

A series of vegetation zones are generally recognizable in the Northern Rocky Moun- tains (Daubenmire, 1943; Daubenmire and Daubenmire, 1968; Habeck, 1967; 1970a, 1970b, 1972). These zones are generally arranged spatially along elevational gra- dients, but often are modified locally by slope and exposure factors; thus, no perfect relation between forest zone and elevation is found. Moisture availability varies with aspect, as well as elevation, but it also varies because of the gradual disintegration of the Pacific coastal influence. Thus, the vegetation changes continually in time and space.

Originally, the lower vegetation zones within the intermontane valleys were cov- ered with grassland, sagebrush, juniper, pine savanna, wet-bottomland, streamside, and marsh communities. The lowest continuous forest zone, which marks a transi- tional change between grassland communities and the more mesic forest zone dominated by Douglass fir (Pseudotsuga menziesii) , was dominated by ponderosa pine (Pinus ponderosa) .

Douglas fir occupies a wide elevational range in the Northern Rocky Mountains, occurring at elevations ranging between 600 and 2800 m (1968 and 9186 ft) . The forest zone dominated by Douglas fir is generally restricted to elevations ranging between 900

and 1500 m (2953 and 4921 ft). The western redcedar/western hemlock forest zone is found just above the Douglas fir zone in much of northern Idaho and in portions of northwestern Montana, where annual moisture reaches 760 mm (30 in.) or more. However, as one moves south toward Mis- soula, only scattered, isolated pockets of this western redcedar/western hemlock zone are found in moist canyons. Those relict, communities of this zone that are found in the vicinity of Missoula are actually depau- perate of many of the floristic elements dis- played in northern Idaho and in Glacier Park.

Where the cedar/hemlock zone is not found in the Northern Rocky Mountains, the upper Douglas fir zone comes in direct contact with the spruce/fir zone dominated by subalpine fir (Abies Zasiocarpa), Engel- mann spruce (Picea engelmannii), lodgepole pine (Pinus contorta), and whitebark pine (Plnus albicaulis) . Communities dominated and/or codominated by mountain hemlock (Tsuga vnertensiana) and subalpine fir are found in high mountain areas along the Idaho-Montana State border.

Many of the same species found in the spruce/fir zone are also found in the timberline forest zone, because the spruce/fir zone extends to elevations over 2800 m (9186 ft). On some high, rocky sites at timberline, alpine larch (La& lay&ii) also occurs. This species is common in the Bit- terroot Mountains at elevations above 2100 m (6890 ft) (Arno and Habeck, 1972). These timberline species are joined on t#he Continental Divide by limber pine (Pinxs flex&s) and by species that surprisingly enough are also found in certain portions of the grassland zone on the lower east slopes of the Divide.

Other tree species also occur within these various zones therefore the total tree flora found in these zones numbers about t,wo dozen species. As a result, compositional variation of these species within and he- tween these forest zones is complex. A portion of this complexity is attribut,ed to as-


pect and climatic factors, but much of it has been influenced significantly by fires.

Low-Elevation Vegetation Types

The drier plant-community types in the intermontane valleys and on the adjacent lower mountain slopes have not remained intact. They have been physically altered by man’s activities, although relict examples of each still exist. Such relict communities, however, often occur on sites that were not easily disrupted by agricultural activities or stock raising and consequently may not be typical in their botanical features. The valley grasslands and associated pine savannas burned periodically during settle- ment by Indians and early white people. Evidence of grassland fires does not persist long, but the occasional occurrence of individual trees or small groups of old-aged, open-grown, fire-scarred ponderosa pines on the margins of the valleys provides some testimony today of the influences of previ- ous fires.

Ponderosa pine savannas have been altered considerably during the past century. The scattered pines mentioned in early fed- eral land surveys no longer exist in some of the valleys. These were removed for croplands or for fuel and building along with the native grasses. Thus, fires that might have earlier originated in the valley grasslands and extended into the mountain forests were modified. Such cultural changes probably had an effect on the pine savanna communities, particularly those dependent upon fire for their continuance. However, a portion of the open ponderosa pine stands in western Montana appear to perpetuate themselves without routine fire treatments because of the severely dry sites upon which they occur. One still can find pine openings that have been maintained by site aridity and high temperatures on south and southwest slopes or on rocky ridges and talus slopes.

Some of the original pine savanna communities occurred within the lower Douglas fir zone as major seral stages; these

eventually were invaded by Douglas fir. Periodic fire in such areas favored the continuance of the pine and delayed successional replacement by Douglas fir. When fire passed through such stands, the competition offered to ponderosa pine by other tree species was altered. Competing seedlings of Douglas fir and shrub species that cast shade over the grassland understories were reduced or removed for extended periods of time. Early white man disrupted the natural regime of fire in these communities.

Ponderosa pine savannas occurring on mesoxeric habitats are presently being invaded by Douglas fir or other mesic species because they cannot perpetuate themselves without fire. For example, ponderosa pine, a rare tree within the boundaries of Glacier National Park, is found in a rather restricted portion on the western edge of the Park. Ayres (1900) was interested in these pines because they formed rather impres- sive savannas. Adjacent to these savannas, isolated grassland communities could be found, but these were quite a distance from extensive valley grasslands. Ayres’ description of this portion of Glacier National Park indicates that fire had been important in the formation of such savannas. He tended to attribute savanna formation to the devastations of fire because the areas lacked dense tree cover.

Today, the grasslands on the west side of Glacier National Park are being invaded at their edges by lodgepole pine, and the ponderosa pine openings have been invaded by Douglas fir and spruce (a hybrid, Picea engelmannii X P. glauca) (Habeck, 1970a; Lunan, 1972). The lack of ponderosa pine reproduction less than 50 yr of age has given rise for concern that this pristine forest community type may be lost from the Park’s vegetation, Recent measure- ments in these stands indicate that fuel accumulations have created a hazard to the ponderosa pine, if fire was immediately re- turned to these areas.

Similar invasions of ponderosa pine


openings occur in the Selway-Bitterroot Wilderness (Habeck, 1972; Aldrich and Mutch, 1973). On the south-facing slopes above White Cap Creek, ponderosa pine occurred nearly to the stream edge of this creek in the past. Engelmann spruce and grand fir presently occupy much of the im- mediate streamside habitats, and advanced Douglas fir reproduction is present beneath

the larger pines. The oldest pines often have large-diameter lower limbs this indicates that these trees grew over a lengthy period of time in the open (Fig. 2). Man has effectively excIuded fire from these pine openings for many decades. Pine saplings generally are present in this zone where there have been fires. Because fire no longer limits Douglas fir invasion, a significant rc-

Fro. 2. Large, unpruned lower limbs indicate that this ponderosa pine developed in a much more open stand in the past.

414 HABECK AND MTJTCH

duction in the area of ponderosa pine can be expected. Pine stands probably can persist on midslope positions above White Cap Creek on sites that are too dry for successful invasions by other tree species; it is too early to determine the ultimate success of Douglas fir expansion into the fire-dependent pine stands.

The Douglas Fir Zone

Within the Douglas fir zone, fire dis- turbance is often followed by the encroach- ment of ponderosa pine (Fig. 3), but its tenure on such sites is limited to a single generation (Habeck, 1967; Schuler, 1968). However, old-aged ponderosa pines might

still be found in old-aged Douglas fir communities. Ponderosa pine’s role as a pioneer invader in this zone is shared by western larch (L&x occident&). Douglas fir within much of its mid-elevation range in the Northern Rocky Mountains can be found on all aspects. However, western larch and ponderosa pine occur on different sites within this zone. Ponderosa pine is known as a major seral species found on warmer and drier aspects, whereas western larch is found on the cooler, more mesic northern aspects. The latter is less apparent within the lower spruce/fir zone and within the moister cedar/hemlock zone, whereas western larch occurs on a variety of aspects.

FIG, 3. PQnderosa pine seedling in fire-created opening.

FIRE-DEPENDENT FORESTS, NORTHERN ROCKIES 4 15

Both ponderosa pine and western larch withstand moderate ground fires. This abil- it,y is attributed to the development in both species of thick bark layers that effectively insulate the trees. These bark layers are developed early in the lives of these trees but are most effective as the trees approach full maturity. Ground fires, however, will de- stroy or reduce in number the young seedlings of both species, but even these young seedlings often can tolerate high temperatures for short durations (Roeser, 1932).

Douglas fir also has morphological adaptations that permit it to survive ground fires. Mature Douglas fir trees develop a thick, corky bark, which affords partial to complete protection from light-to-moderate burns. Douglas fir does not often form savanna-like communities; however, it does occur within semiopen stands with ponderosa pine on some rocky talus slopes. The perpetuation of such semiopen stands might have been enhanced by periodic ground fires, but not necessarily so. Because the dense Douglas fir stands can support des- structive crown fires, the thick bark does not provide as effective a survival mechanism for Douglas fir. The thick-bark fea- ture is known to have been instrumental in the survival of some mature Douglas firs in stands that otherwise would have been consumed by fire. These survivors have served as local seed sources for natural re- generation in such stands. Isolated, old- aged trees with one or more fire scars at their bases frequently can be found throughout the Douglas fir zone in t,his region.

The Cedar/Hemlock Zone

Conspicuous morphological fire adaptations are not found in western redcedar or western hemlock. Both species have rather thin bark, which provides only minimum protection against high temperatures gener- a.ted by ground fires. Redcedar, however, endures the impact of ground fires far better than western hemlock, and occasionally exhibits the ability to survive ground fires,

Such cedars have scars on their outer &em surfaces. Some individual cedars seen have had a narrow strip of intact bark tissue supplying one or more living branches in the crown. We have also observed westcrll hemlock with small fire scars, but these were rare.

Pioneer and seral species in the cedar/hemlock zone are fire-dependent. These include lodgepole pine, western larch, western white pine, and Douglas fir. Habeck (1968, 1970b) reported that fires occurred frequently enough before 1900 in Glacier National Park and that climax stages of forest development usually could not be found. He explained that recurring fires burned through early and intermediate stages of succession in stands dominated by lodgepole pine, western larch, western white

pine, and Douglas fir, rather than in old- aged stages of stands dominated by rcd- cedar and western hemlock.

Before fire control was used as a management action in Glacier National Park, lodgepole pine and western larch were dominant in most communities; in such situa- tions fire maintains this dominance. Appar- ently, the percentage of each species in a given stand depends on the periodicity of fires and the stage of development each species had reached before a succeeding burn. In Glacier Park, lodgepole pine is the most abundant tree species despite over a half century of fire suppression. Man’s protection activities now are contributing to forest-cover alterations that may not have occurred before 1900.

Lodgepole pine stands are reaching maturity in much of the Park. Their understories are supporting advanced reproduction of more shade-tolerant, species, including both redcedar and western hemlock. Some of these stands are receiving competition from Douglas fir and western white pine. Western white pine is common in the seral communities occurring in the vicinity of Lake McDonald. This area is at the eastern range limits of western white pine; evidently climatic factors exist that


prevent this species from demonstrating in Glacier Park the same postfire vigor it exhibits in much of northern Idaho.

In other lodgepole pine stands, the understory consists of dense spruce reproduction and continuous canopies. In such stands in Glacier Park, extremely high amounts of fuel have accumulated. If fire protection is continued in such stands, the potential for fire spread and intensity will be heightened because the accumulation of heavy fuels will be further increased.

In Glacier Park, western redcedar enters pioneer communities at an early stage (Habeck, 1968) because the lightweight, winged seeds of cedar are readily dissemi- nated from existing seed sources. Seedlings develop rapidly in open stands of lodgepole pine and western larch. Cedar seedlings have only a moderate tolerance of shade, not as highly tolerant as western hemlock seedlings. In denser cedar stands, 100-150 yr old, vegetative layering becomes the more important reproductive mechanism. Branches falling from cedar canopies into moist depressions take root producing new individuals, as do young saplings and lower branches pressed down by heavy snowpacks.

Western hemlock invades intermediate stages of forest development well after a continuous forest canopy has been formed. The sexual reproduction of hemlock is highly tolerant of dense shade, but appears to be somewhat dependent upon decaying logs and stumps for germination substrates. On drier upland slopes in Glacier Park, western hemlock often achieves dominance over redcedar, if fires do not occur. Western hemlock rarely replaces redcedar entirely because cedar reproduction and individual trees can usually be found in most size and age classes even in old-age hemlock stands. Redcedar is fully capable of attaining dominance or codominance with western hemlock along streamsides and in other poorly drained habitats. Such examples can be found in Glacier Park, mostly in the midportion of the McDonald Creek Valley,

where widespread fires have not occurred for many centuries. E’lsewhere, where pioneer and other seral communities are most common in the Park, it remains to be seen how these competitive relationships between cedar and hemlock will sort themselves out.

An analysis of 50 yr of Glacier Park fire records (O’Brien, 1969 in Habeck, 1970a) reveals that a very large number of lightning-caused fires have occurred in the cedar/hemlock zone in the sourthwestern corner of the Park. Fires starting before June 20 generally are confined to elevations below 1500 m (4921 ft) ; however, the burn- able zone increases about 185 m (607 ft) every 10 days between June 21 and August 25 up to an elevation of 2500 m (8200 ft). Lightning ignitions most often occur on ridgelines and south-facing aspects.

Without any fire control in Glacier Park, the forests in the cedar/hemlock zone would tend to be continually “recycled” through repeated fires; thus there would be little or no opportunity for extensive development of climax cedar/hemlock stands. This reflects how fire control today can change successional vegetation patterns over large areas. Such control has reduced the production of younger seral community types, and is contributing to an unnatural increase of intermediate- to old-aged stages in this area.

These successional developments also produce unnaturally high accumulations of fuel, which means that diligent fire control will be required for many more decades. It’s doubtful whether such measures will be entirely effective, because of the predictable occurrence of lightning in these hazardous fuels,

In the Selway-Bitterroot Wilderness, the cedar/hemlock zone differs from that found in Glacier Park because the range of western hemlock does not extend into this part of northern Idaho (Habeck, 1972). Many of the drainages within the Selway-Bitter- root Wilderness are lined with mixtures of redcedar and grand fir, but the understory

FIRE-DEPENDENT FORESTS, NORTHERN ROCKIES -1-17

vegetation is very similar to that found farther north and in Glacier Park.

In some of these cedar/grand fir forests, the cedar has not been able to regenerate naturally ; this may indicate that the geographic range of this species is continuing to retreat westward. This suspected retreat may be either temporary or permanent, since the ecological behavior of a tree at its range limits cannot easily be pre- dicted. Nevertheless, this partially com- plicates our interpretations of the role of fire in the Selway-Bitterroot Wilderness.

In most of these streamside redcedar/grand fir forests a few redcedar trees having fire scars can always be found, indi- cating that fires have occurred. In forests along Moose Creek and Bear Creek within the upper Selway River system, redcedar trees 180-240 cm (6-8 ft) in diameter (ages that approach 700 or more years) can be found.

Little change of consequence has taken place within the older cedar groves, despite man’s fire-suppression activities in recent years. However, we still have to determine if periodic ground fires may have enhanced the competitive position of redcedar with grand fir, or whether major regional climatic shifts over the past 500 yr in this portion of the Northern Rocky Mountains have diminished this advantage.

The Spruce/Fir Zone

The spruce/fir zone is found at elevations above 1800 m (5900 ft) and is dominated by subalpine fir, Engelmann spruce, lodgepole pine, whitebark pine, and other coni- fers. This zone has been subjected to nearly the same kind of fire occurrence as those zones at lower elevations, despite the fact that cooler and moister conditions are found there. More climax communities are found in this zone than in lower forest zones, but the complex mosaic of various- aged seral communities is still present. The rocky topography existing at higher elevations in many of the Northern Rocky

Mountain ranges also contributes to these complex vegetation patterns.

In the spruce/fir zone, community processes are slowed by the short growing seasons and lower temperatures. Consequently succession following fires does not proceed rapidly. Therefore the effects of 50 yr of fire suppression are not as discernible in the spruce/fir zone as is true in vegetation zones at lower elevations. Frequent fires are not needed to maintain biotic diversity at these high elevations; the effects of fires that do occur are long-lasting (Fig. 4).

Lodgepole pine often is the major pioneer tree species establishing itself following fire in this zone. Western larch and Douglas fir also occur as pioneer species in the lower edge of the spruce/fir zone, but neither will be as dominant as lodgepole pine. When Engelmann spruce germinates heavily on burned sites, it can become the dominant pioneer species in this zone. Obviously, the exact composition of the pioneer and devel- oping seral communities is highly variable, because it is dependent upon many factors existing at the time fires occur (e.g., the intensity of the fire and the number and kinds of seed-producing tree species that survive in the area). Studies of forest succession have revealed that recovery patterns are more predictable in forests in lower zones than in the spruce/fir and t,im- berline forests. However, there are known instances where combinations of the potential climax species (subalpine fir, whitebark pine, and mountain hemlock) have re- invaded spruce/fir forests immediately after fire. Centuries-old communities of subalpine fir, whitebark pine, we&rn hemlock, and Engelmann spruce are not often found. In some such old-age communities, Engelmann spruce assumes a role of a dominant seral species; in others. it serves a codominant role.

At timberline, where forest cover often becomes discontinuous, western larch is not found and Douglas fir is present only rarely. Locally, in different mountain ranges, alpine larch or limber pine join


FIG. 4. Vegetation response proceeds more slowly at higher elevations following a 19% fire in the Selway-Bitterroot Wilderness.

Engelmann spruce, subalpine fir, lodgepole pine, whitebark pine, and mountain hemlock. Forest recovery processes at timberline are extremely slow, and disruptions caused by fire, rockslides, or snow ava- lanches are easily detectable for a century or more. Although forest cover may not always be continuous at timberline, which might suggest the existence of some areas that have been exempt from past fire, this has never proven to be the case in our experience ; searching has always yielded some charcoal.

High-elevation fires have occurred recently in Glacier Park (Habeck, 1970a) ; observations of these fires showed that a well-established fire can travel successfully through upper spruce/fir and timberline zones. For example, a fire that occurred in the 1930s successfully crossed the Conti-

nental Divide through a pass located above 2150 m (7054 ft). Furthermore, we believe that some amount of the present-day alpine vegetation in Glacier Park occupies sites that once supported krummholz timber before it was removed by fire. Apparently, the pace at which the forest reestablishes itself above 1850 m (6070 ft) in Glacier Park has produced a downward extension of alpine species; these remain until the forest rein- vasion occurs (Habeck, 1969).

FIRE DEPENDENCY AND ECOSYSTEM STABILITY

The effects of wildland fires on ecosystems have been well documented (Lutz, 1956; Ahlgren and Ahlgren, 1960; Cooper, 1961; Daubenmire and Daubenmire, 1968). Two recent papers (Loucks, 1970; Mutch, 1970) have dealt with the effects of the


interaction between fire and evolutionary and successional developments of plant communities.

Mutch (1970) hypothesized that fire- dependent plant communities burn more readily than non-fire-dependent communities because natural selection has favored development of characteristics that make them more flammable. This hypothesis recognizes that plant species that have survived fires for tens of thousands of years may not only have selected survival mecha- nisms but also inherent flammable properties that contribute to the perpetuation of fire-dependent communities. However, Mutch did not mean to imply that fire dependency and non-fire-dependency are the only events that evolved, because the time dependency of flammability causes a spec- trum of fire frequencies.

Flammability is an interaction between plant communities and environment over time. Practically every dry season a significant fire is possible in such communities as grasslands, ponderosa pine, and savanna woodlands, because these communities bring certain properties to the ecosystem t,hat enhance ff ammability. Under natural conditions, characterized by frequent fires, these communit’ies would generally experience lower-intensity fires than other communities ; thus, their composition and structure are maintained by periodic fires because inherent characteristics enhance fire spread. However, the potential for spreading fires is not readily available in all plant communities. A physical deterioration over time is often the factor that finally induces high flammability in lodgepole pine, spruce, and north-slope communities in the Northern Rocky Moun- tains. This deterioration of stands leads to high-intensity fires that eventually causes stand replacement within these forest communities.

Bloomberg (1950) described how the accumulation of windfall and other organic matter over long periods of time resulted in a high fire hazard in a spruce/fir forest.

In this forest, lightning strikes no longer caused merely spot burns but major con- flagrations during exceptionally dry seasons.

The flammability of forest fuels in the Northern Rocky Mountains is controlled by variations in plant succession and fuel succession in time and space. The spectacu- lar fires are readily recalled; however, the effects of limited burns and low-intensity fires on ecosystems and vegetation mosaics are also meaningful.

The fire dependencies of ponderosa pine, savanna woodlands, and many grassland communities are readily discernible because high fire frequencies often result in competitive advantages. In other communities, even much longer fire frequencies might also contribute to such fire dependencies. For example, Loucks (1970) hypot8hesizecl upon t,he ecological significance of recurring disturbances of varying intervals:

I offer the hypothesis that evolution in ecospskms has brought about not onl~ adapt,ntion to heterogeneous environments, hut adaptation to a repeating pattern of changing rnvironm:>nts, a stationary process that represents a composite of timr interc:ik over which replacementr of speries is repeab! over and over again. The periodicity ranges from several centurirs in the northern lake forest, where white pine seems t,o have hecn recycled at intervals of 300-400 years, through the shorter intervals in the deciduous foresis of the Mississippi Valley, to periods of a fell decades and pvpn annually at the edge of the grasslands.

Loucks also said that these perturbations tend to recycle the system and maintain a periodic wave of peak diversity. He con- cluded that any modifications of the system that preclude periodic, random perturbation and recycling would be detrimental to the system.

Wildland fires traditionally have been viewed as (a) a negative and destructive force, or (b), at best, a transitory dis- turbance in forest systems, or (c) a “tool of management.” In view of our condi- tioned attitudes regarding fire, we may be suggesting solutions to ecosystem functions


and land-management problems that disre- gard fundamental relationships because we have not asked the right questions. For example, Olson (1963) never asked the question: Is fire a decomposer? Instead, he utilized an exponential model to predict steady-state levels of energy storage based only on the balance of producers and decomposers in ecological systems. His analysis showed that many ecosystems in northern latitudes for centuries continue to show positive net litter-production levels.

Daubenmire and Daubenmire (1968) in- dicated that fire incidence in Northern Rocky Mountain stands reaches a prob- ability of certainty in 450-500 yr. In many stands, the fire cycle is much shorter than this. The enigma, then, is this: If fire serves as a decomposing agent, can we adequately manage coniferous ecosystems without ac- counting for the cyclic role of fire? Such an omission would certainly lead to dis- continuities in our comprehension and management of food chains, energy flow, and nutrient cycling within these systems.

The world’s most highly productive forests, the tropical rain forests, are also characterized by their low level of net accumulation of litter (Bray and Gorham, 1964). In Lindeman’s (1942) successional theory for the cool-temperate lake system, senescence of the lake began when organic- matter production greatly exceeded decomposition rates, Does a similar senescence, or regressive productivity, occur in coniferous forests as litter production exceeds decomposition rates? Do population oscillations in cool-temperate regions, even lethal oscillations, contribute toward ecosystem stability over time because they serve to compensate for the multiplicity of energy conversion pathways characteristic of equatorial regions (but not present in higher latitudes)? We know that the ac- tivity of decomposing organisms is limited in cool-temperate regions and organic debris accumulates over time. Fire may be the oscillatory agent in higher latitudes that serves a vital role in energy conversion.

In the classical sense, stability in an eco-

system implies that such an ecosystem is free from oscillations (Dunbar, 1960). Some interesting questions are posed by Dunbar’s comparisons of the highly stable production systems of tropical waters with the seasonal and longer-term oscillations of temperate and polar waters. He hypothesized that population oscillations are an expression of the immaturity of a system and contrasted this with the stability of the more mature adapted floras and faunas.

Dunbar’s concepts provide an interesting frame of reference within which to consider ecosystem adaptations to equatorial and cool-temperate climates. He assumes that oscillations are bad for any system and that violent oscillations are often lethal. However, we believe other judgments might be reached, if you don’t begin with his be- lief that population oscillations are cate- gorically “bad.” How can anyone judge that oscillations, even lethal ones, are bad in the functioning of biological systems? Is it even valid to extrapolate such a premise from an equatorial climate and apply it to a cool-temperate one?

Dunbar stated that climatic and seasonal oscillations do not occur in tropical and subtropical environments. This fosters more complex ecosystems in such environments, he added, which contain many energy pathways along which overloadings can be re- leased. This last statement may be the key in critically looking at his argument.

Admittedly, numerous pathways do exist in tropical forests that speed up energy conversion processes; the most important of which are the high rates at which micro- bial and fungal decomposition occur. How- ever, aren’t the fire cycles observed by Whittaker and Woodwell (1969)) Habeck (1970a), Vogl (1970), and Loucks (1970) just as valid an approach to any considerations of stability and the viability of higher-latitude ecosystems?

We might hypothesize that terrestrial ecosystem stability is sustained when heating levels are commensurate with energy conversion requirements. By so doing, it


then becomes immaterial whether heating rates are continuous (equatorial and micro- bial heating) or cyclic (wildland fire heating).

Understanding fire’s role within wildland ecosystems will help describe the amplitude of present-day fire perturbations. Highly flammable properties of plants might be detrimental to the functioning of ecosystems under programs of attempted fire exclu- sions, because the accumulation of flammable fuels over a long period of time on some sites may lead to fires of unnatural intensities. Of equal concern would be the introduction of fire at shorter intervals than the system experienced naturally.

Slobodkin and co-workers (1967) defined the balance of nature as the persistence of ecological systems as a result of their ten- dency to compensate for perturbations; however, we might question the amplitude of the fire perturbations today. Odum (1969) emphasized that pulse stability occurs only if there is a complete community adapted to the particular intensity and fre- quency of perturbation:

Adaptation-operation of the selection process-requires time measurable on the evolutionary soale. Most physical stresses in- troduced by man are too sudden, too violent, or too arrhythmic for adaptation to occur at the ecosystem level, so severe oscillations rather than stability results.

The large fires that occurred in central Washington, southern California, Florida’s Everglades, and northern Minnesota in 1970-1971 might be viewed as examples of severe oscillations rather than signs of oscillatory stability in ecosystems that had adapted to fire. In taking such a view we would be attributing the cause to man’s relatively recent use of fire control in these ecosystems.

WILDERNESS FIRE MANAGEMENT : PRACTICAL CONSIDERATIONS

Knowledge showing how wildland fires tend to stabilize fire dependent ecosystems can be utilized to fulfill the philosophy of

the Wilderness Act of 1964; that is to pcr- petuate areas that are “affected primarily by the forces of nature.”

Any management action plan to restore a natural incidence of fire in an ecosystem would require much more than an understanding of the role of fire cycles and fire frequencies in the various plant communities. It would have to be based on (a) fuel inventory and appraisal data, (b) fire spread and intensity predictions, (c J understanding of plant succession and fuel succession, (d) landform types, and (c) the area’s fire history, as well as including com- prehensive pre-attack planning.

What does wilderness fire management mean? It is not a policy of simply letting fires burn. It is a pre-planned program that insures a more nearly natural incidence of fire in wildernesses.

First, it means understanding fire as a process in wildland ecosystems; what fire does and what it doesn’t do. Such an understanding would entail only an objective ac- counting of the physical and chemical influences of fire on biological systems and the effects of biological systems on fire.

Second, it means the integration of our knowledge of fire processes with the management objectives for specific land units. This is the management phase that actually applies specific prescriptions to the ground.

Third, it means the application of con- s training principles to these prescriptions so that the results of management actions are evaluated. This provides a feedback mechanism whereby prescriptions may be periodically updated and improved.

In itself, a fire-management plan should consist of the following:

1. Basic assumptions for the total management area.

2. Prescriptions on a zone-by-zone basis-what will be done and where.

3. Pre-attack plans on how fires will be managed once they occur and where management action will be taken.

In order to provide the necessary data for wilderness fire management planning in the Selway-Bitterroot Wilderness, the


White Cap Wilderness Fire Study was started in 1970 (Aldrich and Mutch, 1973). Objectives of this study are to:

1. Develop inventory methods that relate fire management to the wilderness resource.

2. Determine relationships between fire and wilderness ecosystems.

3. Determine strategies for a more nearly natural incidence of fire in wilderness.

The study area, approximately 260 sq km (100 sq miles), is located in the Bad Luck and White Cap Creek drainages of the Selway-Bitterroot Wilderness in northern Idaho. These drainages are characterized by a wide diversity of plant communities from shrubfields and ponderosa pine savannas along the breaks of the Selway River at 900 m (2950 ft) elevation to alpine larch communities along the crest of the Bitter- root Mountain range at 2400 m (7875 ft). Over a 45-yr period, 212 fires have been re- corded, of which 97% were started by lightning. Fire-control efforts have been effective in suppressing 154 of these all of which were 0.1 ha (l/4 acre) or less in size. This successful record of fire suppression makes the White Cap study area an excellent out- door laboratory for determining the effects of fire control on plant communities and fuels.

This study has included such investigations as (a) fuel inventory and appraisal, (b) a quantitative analysis of plant communities, (c) a reconnaissance of habitat types, (d) an analysis of landforms, as well as data pertaining to the area’s fire history, hydrology, and fishery resources. Results to date have provided the necessary data to combine 18 land types and 10 habitat types into five ecological land units: (1) shrubfield, (2) ponderosa pine savanna, (3) ponderosa pine/Douglas fir, (4) north-slope communities, and (5) subalpine. Ecological land units are recognizable subdivisions of the landscape that are equivalent in terms of topography, vegetation, fuels, and fire potential. Specifically, there are consistent

similarities within these units as well as significant differences between units. Eco- logical land units are used for implement- ing fire-management prescriptions applicable to those specific zones.

The fire-management plan for the White Cap study area (Table 1) was approved by the Chief of the Forest Service in August 1972. Management prescriptions are related to on-the-ground conditions in each of the five ecological land units, or fire- management zones. The prescriptions also take into account the important factors of human safety, fire-weather, and constraints of pre-attack planning.

A lightning-caused fire in the shrubfield zone on August 18, 1972, was the first fire to be handled under the new fire-management plan. The fire was monitored by air and ground observation and went out naturally after 4 days at a final size of approximately 7.3 by 7.3 m (24 by 24 ft).

Current studies and fire-management programs in wildernesses and national parks provide opportunities to better understand relationships between fire and vegetation diversity, as well as the effects of (a) successional development of flammability on plant communities, (b) effects of fire-control practices on plant communities and fuels, and (c) effects of continued fire suppression on wilderness ecosystems. Knowledge and strategies are now at hand to begin to return fire to wilderness ecosystems. However, following 50 yr of fire suppression, these strategies must be based on an understanding of time-dependent relationships between forest productivity and flammability.

The idea of truly dedicating certain areas to the perpetuation of naturally evolving plant and animal communities has merit. Such communities have esthetic and educa- tional appeal and one day may be important as field laboratories to provide us with the vital links toward a better comprehension of food chains, nutrient cycling, and energy flow. Such knowledge would provide management constraints applicable to all


TABLE 1

SUMMARY OF WILDERNESS FIRE-MANAGEMENT PRESCRIPTIONS FOR

WHITE CAP STUDY ARES, SELWAY-BITTERROOT WILDERNESS

Management zone Suppression Observation Observation + suppression

1. Shrubfield a. Hunting season: a. Prehunting season BUIa > 170

b. Along study boundaries b. Hunting season: BUI <170

a. Fires approaching Wapiti Creek Ridge

2. Ponderosa pine savanna

a. BUI <170 a. BUI >170

3. Ponderosa pine/ a. < 1372 m (4500 ft) a. >1372 m (4500 ft) a. >1372 m (4500 ft); Douglas fir elevation elevation; BUI < 170 BUI >170

4. North slope a. Along study boundaries a. West of Peach Creek a. BUI >170; fires ap- Drainage proaching Peach Creek

buffer b. BUI >170: Peach b. Upper White Cap unit

Creek Drainage

5. Subalpine a. Along study boundaries a. Season-long a. BUI >170; fires approaching Bitterroot, Crest passes

b. BUI >170: Bitterroot Crest passes

a BUI: Buildup Index of the National Fire-Danger Rating System.

wildlands to maintain the viability of biological systems. Consequently, the perpetuation of unmodified ecosystems in wilderness could benefit all members of so- ciety, not only those who visit them.

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