fire-dependent forests in the northern rocky mountains
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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 relation- ships 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 dont understand all of the long-term consequences of fire control in those forest communities that have evolved fire-dependent characteristics.
Large areas have been established as na- tional parks and wildernesses in the North- ern Rocky Mountains. Their management calls for the perpetuation of all natural for- est 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 character- istics (e.g., changes in soil moisture or nu- trient 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 influ- enced by periodic fires will have a modify- ing influence that is detectable and measur- able (Fig. 1).
Fire-dependent forest ecosystems require fire treatment for their continued perpetua- tion on the landscape. The competitive suc- cess of fire-dependent species is directly re- lated to the selection of characteristics that improve the fitness of populations in the fire environment of the Northern Rocky Mountains. Many species here exhibit mor- phological and physiological adaptations that provide survival advantages on land- scapes 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
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-depen- dent 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
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 inter- montane 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 light- ning storms, combined with the drying for- est 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
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 au- thor has had comparable experience in the study of forest fuels in many different for- est ecosystems. During their field work, di- rect evidence could usually be found that past fires had influenced most plant com- munities. 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 pat- terns and species relationships can readily observe that a high percentage of the vege- tation, 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, be- cause many stages of successional develop- ment can usually be found in each forest zone.
Written historical descriptions of the re- gions 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 vege- tation 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 de- pendency 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,