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Quinney Natural Resources Research Library, The Bark Beetles, Fuels, and Fire Bibliography S.J. and Jessie E.

1973

Fire in the Virgin Forests of the Boundary Waters Canoe Area, Minnesota

Miron L. Heinselman

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Recommended Citation Heinselman, M. (1973). Fire in the virgin forests of the Boundary Waters Canoe Area, Minnesota. Quaternary Research, 3(3): 329-382. doi: 10.1016/0033-5894(73)90003-3

This Article is brought to you for free and open access by the Quinney Natural Resources Research Library, S.J. and Jessie E. at DigitalCommons@USU. It has been accepted for inclusion in The Bark Beetles, Fuels, and Fire Bibliography by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. QUATERNARY RESEARCH 3, 329-382 (1973)

Fire in the Virgin Forests of the Boundary Waters Canoe Area, Minnesota

MIRON L. HEINSELMAN’

Fire largely determined the composition and structure of the presettlement vegetation of the Boundary Waters Canoe Area as well as the vegetation mosaic on the landscape and the habitat patterns for wildlife. It also influenced nutrient cycles, and energy path- ways, and helped maintain the diversity, productivity, and long-term stability of the ecosystem. Thus the whole ecosystem was fire-dependent. At least some overstory elements in virtually all forest stands still date from regeneration that followed one or more fires since 1595 A.D. The average interval between significant fire years was about 4 yr in presettlement times, but shortened to 2 yr from 1868 to 1910 during settlement. However, 83% of t,he area burned before the beginning of suppression programs resulted from just nine fire periods: 1894, 1875, 18634, 1824, 1801, 1755-9, 1727, 1692, 1681. The average interval between these major fire years was 26 yr. Most present, virgin forests date from regenerat,ion that followed fires in these years. Significant areas were also regenerated by fires in 1903, 1910, 1936, and 1971. Most major fire years occurred during prolonged summer droughts of subcontinental extent, such as those of 1864, 1910, and 1936. Many fires were man-caused, but lightning ignitions were also common. Lightning alone is probably a sufficient source of ignitions to guarantee that older stands burned before attaining climax. Dry matter accumulations, spruce bud- worm outbreaks, blowdowns, and other interactions related to time since fire increase the probability that old stands will burn. Vegetation patterns on the landscape were influenced by such natural firebreaks as lakes, streams, wetlands, and moist slopes. Red and white pine are most, common on islands, and to the east, northeast, or southeast of such firebreaks. Jack pine, aspen-birch, and sprout hardwood forests are most, common on large uplands distant from or west of such firebreaks. A Natural Fire Rotation of about 100 yr prevailed in presettlement times, but many red and white pine stands remained largely intact for 150-350 yr, and some jack pine and aspen-birch forests probably burned at intervals of 50 yr or less. There is paleoeco- logical evidence that fire was an ecosystem factor before European man arrived, and even before early man migrated to North America. Probably few areas ever attained the postulated fir-spruce-cedar-birch climax in postglacial times. To understand the dynamics of fire-dependent ecosystems fire must be studied as an integral part of the system. The search for stable communities that might, develop without fire is futile and avoids the real challenge of understanding nature on her own terms. To restore the natural ecosystem of the Canoe Area fire should soon be reintroduced through a program of prescribed fires and monitored lightning fires. Failing this, major unnatural, perhaps unpredictable, changes in the ecosystem will occur.

INTRODUCTION ha.) remnant of the natural ecosystems of The Boundary Waters Canoe Area, a Minnesota’s Laurentian Shield country unit of the American Wilderness Preserva- 1 Sorth Central Forest Experiment Station, U.S. tion System within the Superior National Forest Service, Folwell Avenue, St.. Paul, Minne- Forest, contains a 532,000-acre (215,000 s0t.a55101.

329

Copyright @ 1973 by University of Washington. All rights 01 reproduction in any form reserved. 330 HEINSELMAN

Fro. 1. Location of study area (bounded by heavy line) and of the remaining virgin forests of the Boundary Waters Canoe Area (shaded areas).

(Fig. 1). Both the flora and fauna of the re- researches of Swain (1972, this symposium), maining virgin areas2 are nearly intact. leave no doubt that fire was a dominant Even the area’s largest carnivore, Canti lu- factor in the entire primeval system. Fire pus, the endangered eastern timber wolf, largely determined the species composition, still maintains a viable population. We have age structure, and mosaic of successional long known that fire was a factor in the stages of the forests, and thus also the habi- ecology of the Great Lakes conifer forests tat patterns for wildlife. It was also a (Ayres, 1899; Maissurow, 1935; LeBarron, major factor controlling nutrient cycles and 1939; Spurr, 1954), but an ecosystem view energy pathways, and in maintaining the of its influence was hampered by lack of diversity, productivity, and stability of the knowledge of the historical role of fire in a whole ecosystem. But the crucial ecological complete functioning natural ecosystem role of fire has not been recognized in the such as the Canoe Area’s. Canoe Area’s management, and fire exclu- My fire history studies conducted from sion has been a nearly achieved manage- 1966 to 1972, reported here, and the related ment goal for 60 yr. Thus this area is the principal Wilderness *The virgin areas of virgin forests are those Area in the central and eastern United areas or forests never directly altered by man States that contains the elements of a grow- through logging, land clearing, tree planting, farm- ing national dilemma. For we must soon re- ing, mining, road building, or similar activities. introduce fire into such fire-dependent eco- Essentially all areas have burned in the past 400 yr, and many virgin forests are postfire succes- systems or accept major unnatural, perhaps sional communities 110 yr or less in age. Virtually unpredictable, changes in the plant, animal, all of the natural forests still contain first-genera- and environmental complex. The problems tion postfire stand elements, and I include all are similar in principle to those in many such forests in the term virgin. To do otherwise other major nature reserves. Resolving this would require setting a totally arbitrary stand age beyond which the forests would be called dilemma will test both our competence to virgin. apply ecological principles to nature-pres- FIRE AND THE NATURAL ECOSYSTEM Xi 1

ervation problems and our commitment to parallel, low ridges with locally st,eep retain or restore some essentially natural scarps. Local differences in elevation range ecosystems. between 30 and 150 m. Most of this relief is related to the contours of the pre-Cam- ECOSYSTEM CHARACTERISTICS brian bedrock: granite, gabbro, graywacke, The Canoe Area stretches for 110 miles felsite, slate, schist, greenstonc, and con- (177 km) along the U.S.-Canadian bound- glomerate (Sims, 1970). The area was gla- ary, ranging from 10 to 30 miles (l&48 ciated repeatedly during the Pleistocene, km) in width. Its gross area is 1,030,OOO the final advance being the Vermillion acres (417,000 ha.), of which about 172,000 phase of the Rainy Lobe, during the late acres (69,000 ha.) are in lakes and streams Wisconsin glaciation (Wright and Watts, over 10 acres (4 ha.) in size.3 1969). Deglaciation occurred about 16,000 Situated near the center of North y.a. (Wright, 1971). Glacial scouring pre- America, the region has a cool continental dominated over deposition, and the scant climate, with short warm summers and long covering of till, outwash, and lacustrine de- cold winters. Annual precipitation averages posits varies strongly over short distances. about 71 cm (28 in.), 64% falling as rain Coarse-textured, heterogeneous soils during the growing season-May through formed on gravels, sands, or boulder till are September. The mean annual temperature usual, but lacustrine clays also occur. Bed- is 2OC (36OF) ; the mean July, 17% rock is exposed on many ridgetops, cliffs, (63OF) ; the mean January, -15OC (6OF) and lakeshores. A labyrinth of over 1000 (Baker and Strub, 1965; Baker et al., interconnected lakes and streams occupies 1967). Temperature and precipitation vari- the bedrock troughs and basins. Thousands ations from these norms are marked, and of filled-lake bogs and forested peatlands significant droughts occur every few years. have overspread the lowlands. Prolonged droughts, with precipitation only The biotic communit#ies are transitional 50-700/o of normal for 1 or more years, have between the Great Lakes-St. Lawrence and occurred several times in the century since boreal forest regions of Rowe (1959). The weather records became available. The boreal trees are abundant: jack pine mean annual snowfall is about 152 cm (60 (Pinus banksiana), black and white spruce in.), and the ground is normally snow-cov- (Picea mariana, P. ylul~a), balsam fir ered from mid-November to late April. (Abies bnlsamea~, tamarack (1,nri.c /ali- Late-winter snow accumulations of 50-100 cina) , northern white cedar iThuja cm (20-40 in.) are usual. Thunderstorms occident&), quaking aspen (Populus tre- are common from May through September, mutoides), and paper birch (Bet&a papy- and lightning ignition of forest fuels during rifern). But so are the two pines char- dry storms is common. Prevailing winds are acteristics of the Great Lakes Forest--the from the west, especially during dry eastern whit’e pine (Pinus strobll.s) and red weather. pine (P. resinosa). Red maple (Acer rub- The area is within the Laurentian Up- rum), northern red oak (Querrus mI)rcI I, land physiographic province (Fenneman, American elm (171nzusamericnncr) , black ash 1938). Its landscape, of generally slight re- (Frazinus nigra) , bigtooth aspen (Popdzrs lief, is broken by numerous, occasionally grandidentata) , and balsam poplar (Popu- Zus balsamifera) also occur on certain sites. ‘Hereafter land measures are in the English Basswood (Tilin american.a) and yc~llow units acres (I acre = 0.40 hectares, or 1 ha. = 2.47 birch (Retula alleghaniensis) are rare. acres), or miles (1 mile = 1.61 kilometers or 1 Conspicuous by their absence are sugar km = 0.62 mi.), because all maps and public records for the Canoe Area are in these units, maple (Acer saccharum), beech (Fagws and the U.S. land survey grid exists on the ground. grandifolia) , and eastern hemlock (Ts?/na 332 HEINSELMAN

TABLE 1 land forests have been quantitatively de- AREA OF VIRQIN LANDSCAPEO BY PLANT COM- scribed and classified by O.hmann and MUNITIES IN THE BOUNDARY WATERS CANOE Ream (1971a, b), and Grigal and Ohmann AREA, MINNESOTA, JANUARY 1973 (1973) Table 1). The jack pine communi- Virgin Virgin ties are the most abundant types today areas, areas, even after 60 yr of attempted fire exclusion. all all The broadleaf group, dominated chiefly by Plant communityb zones zones aspen and birch, is a close second. White Acres Percent pine and red pine communities comprised Upland types only 10% of 106 randomly sampled virgin Lichen outcrop 20,900 4.7 stands (Ohmann and Ream, 1971b). The Jack pine-oak 20,900 4.7 Red pine 17,300 3.9 wetland communities have not been fully Jack pine-black spruce 49,900 11.2 treated, but a preliminary study by Dean Jack pine-fir 28,000 6.3 (1971) suggests that they are closely re- Black spruce-feathermoss 28,000 6.3 lated to peatland communities of the gla- Aspen-birch 28,000 6.3 cial Lake Agassiz region, 100 miles to the Aspen-birch-white pine 20,900 4.7 Maple-aspen-birch 31,400 7.1 west (Heinselman, 1963, 197Oc). Earlier Maple-aspen-birch-fir 28,000 6.3 studies by Buell and Niering (1957) and Fir-birch 71,300 16.0 Maycock and Curtis (1960) described some White-cedar 17,300 3.9 of the spruce-fir communities of this region. Total upland types 361,900 81.4 Most of the common trees, shrubs, and Lowland types herbs have developed means to reproduce Mixed conifer swamp 2200 .5 following fire, although these features have Black spruce bog forest 32,100 7.3 been studied for only a few species (Ahl- Tamarack bog forest 400 .l Sphagnum-black spruce bog 9300 2.1 gren and Ahlgren, 1960; Fowells, 1965). Azh-elm swamp 400 .l Most striking are the serotinous cones of Shrub carr 11,100 2.5 jack pine (LeBarron and Eyre, 1939; Marsh and open muskeg 19,500 4.4 Beaufait, 1969; Roe, 1963; Cayford, 1971), Open water communities 7100 1 6 the semiserotinous cones of black spruce Total lowland types 82,100 18.6 (LeBarron, 1939; Heinselman, 1957)) and Total all communities 444,000 100.0 the root suckering and light seeds of quak- Lakes and streams 88,000 - ing aspen (Fowells, 1965). The fire resis- Total virgin areas 532,000 - tance of mature, thick-barked red and a Virgin areas are those never logged, cleared, white pines is well known, but specific roaded etc. Nearly all areas have burned within studies are lacking. To reproduce, individ- the past 400 yr. Only solid contiguous tracts within generally uncut regions are included. uals of these species must survive the fire, b Upland plant community types from Grigal because good seed crops are intermittent and Ohmann (1973), after Ohmann and Ream and their cones are neither persistent nor (1971b). Lowland types adapted from Superior serotinous (Van Wagner, 1971). Blueberries National Forest Timber Management Plan July 1, 1964-July 1, 1974 for Extensive Zone BWCA. ( Vaccinium angustifolium and V. myr til- loides) may reproduce by sprouting from the roots, which are usually not burned out, canadensis) , the climax dominants often as may beaked hazel (Corylus cornuta) identified with the Great Lakes-St. Law- (Buckman, 1964b), mountain maple (Acer rence forest. Ktichler (1964) has mapped spicatum), and green alder (Ahus c&pa), the potential natural vegetation of the common tall shrubs. Paper birch, red Canoe Country as Great Lakes Pine Forest maple, and red oak reproduce by sprouting and Great Lakes Spruce-Fir Forest. from the root collar as well as by seeding. The plant communities of the virgin up- Some species are easily fire-killed but FIRE AND THE NATURAL ECOSYSTEM xi3

maintain themselves through their ability styles seminomadic. Firearms, flint and to compete well on moist sites and topo- steel, and other European trade goods prob- graphic situations that usually prevent a ably did not come into general use until t,hc clean burn (valleys, lower slopes, islands, fur trade began, near 1730. The native pop- lakeshores, edges of wetlands). White ulation of the entire Rainy River count,ry spruce, balsam fir, and northern white was about 450 individuals in 1823 (Nute, cedar seem to fit this pattern. Some plants, 1941). By 1885, when European settlements such as Aralia hispida, Corydalis semper- adjacent to the Canoe Country began to virens, and Geranium Bicknellii, occur spring up, there were small Indian villages sparingly on land not burned for many on Lac LaCroix and Kawnipi on the (‘a- years but reappear abundantly and flower nadian side of the border, and near the profusely the first year following fire (see present towns of Tower, Winton, Ely, Nett, Ahlgren, 1960 for details). Lake, and Grand Portage on the American The mammals and birds of the Canoe side. Deliberate burning of some jack pine Country also reflect its position on the land to stimulate blueberry production was Boreal-Great Lakes forest ecotone. Among practiced, at least by the late 19th century. species with boreal affinities are the moose But the extent of this practice in earlier (Alces alces) , Canada lynx (Lpnzr canaden- times, or of the burning of forest to drive si.s), fisher (Martes pennanti), pine marten game, improve hunting, or in tribal war- (Martes americana), snowshoe hare (Lepus fare, has not been established. americana), spruce grouse (Canachites The ‘Voyageurs era” of the French and canadensis) , Canada jay (Perisoreus cana- English fur trade began in 1731 with the densis), and (formerly) the woodland cari- building of a trading post on Rainy River bou (Rangifer caribou). Species more typi- by La Verendrye (Nute, 1941). These peo- cal of the Great Lakes forests are the ple did not farm, clear the forests, or build northern white-tailed deer (Odocoileus vir- permanent settlements, except very locally. ginianus), and bobcat (Lynx rufus), while Most of the trapping was done by the In- the following range (or formerly ranged) dians, and the Voyageurs functioned chiefly widely over both regions: (eastern) timber as traders and in transporting the catch to wolf, red squirrel (Tamiasciurus hudsoni- European markets. The heyday of the fur cus) , red fox (Vulpes fulva) , beaver (Cas- trade lasted barely a century, and the fur tor canadensis) , otter (Lutra canadensis) , traffic along the border canoe route declined mink (Mustella &son), black bear (Ursus to a low level when the Grand Portage Post americanus), ruffed grouse (Bonasa umbel- was abandoned in 1804. The impact of the lus), bald eagle (Haliaeetus leuco- Voyageurs on the ecosystem seems to have cephalus), and others. been mainly to reduce the populations of furbearers-especially the beaver, pine CULTURAL HISTORY OF REGION marten, fisher, and wolverine. Even this European man apparently did not di- effect was temporary: beaver and fisher are rectly contact the Indians north of Lake abundant again, although the marten and Superior until the explorations of Radisson wolverine are still rare. and Groseilliers, about 1660 (Nute, 1941). A period of exploration, minerals pros- About this same time the Chippewa pushed pecting, and land claimstaking followed the the Sioux out of that region. Until about fur trade, from 1820 to 1900. Exploration 1700 these native people probably engaged was limited to canoe travel until a wagon in their traditional hunting, fishing, and road, the Vermillion Trail, linked Duluth gathering of wild rice, berries, and maple with Lake Vermillion in 1869. Railroads did sugar, little affected by European ways, not reach the region until the iron mines at Their populations were low, and their life- Tower and Ely were opened between 1884 334 HEINSELMAN and 1890. The prospectors, speculators, and tered areas of older forests that clothed settlers were extremely careless with fire three-fourths of the region were little and must have caused many of the burns affected by this early logging era. They of that era (Ayres, 1899; Braniff, 1903; were left for worthless, to become the nu- Higgins, 1908). But again they built no cleus of the Superior National Forest, cre- permanent settlements within the Canoe ated from the remaining public domain by Area. A few dozen homesteaders’ cabins President Theodore Roosevelt in 1909. It were built from local timber, and a few is this forgotten land that is the legacy of small gardens were cultivated briefly, but virgin forests of the Canoe Area today. these were soon abandoned as the poor There was little appreciation of the eco- agricultural potential became clear. logical role of fire at the turn of the cen- About 1895 timber cutting for sawmills tury. Most government reports describing at Tower and Winton reached portions of the public domain deplored the ravages of the present Canoe Area. White and red pine fire and considered the forests to have been were the main species sought, and only old “destroyed” by the fires of the 19th cen- trees (generally 100-350 yr old) were large tury. Such fires were always ascribed to enough. But, because of a long history of human carelessness, and there was no rec- fires, only about 20% of the region sup- ognition that lightning ignitions were also ported mature pines (Ayres, 1899). A popu- common and natural. Few could have lar account of the early logging has been imagined that the regeneration already es- published (Heinselman, 1969), and just a tablished on those burns would become a few points need be added. First, it is pre- hotly contested timber resource in less than cisely because recurrent forest fires had a century. For example, consider this from kept three-fourths of the region in recent a public domain withdrawal report of E. A. burns and commercially immature forests Braniff (1903) : that only a small fraction of the Canoe Area was subjected to the usual logging The lands were once covered with a forest of conifers, but almost all of it has been practices of this era. Most of the older burned over and replaced by a dense growth stands were “high-graded” for the best of aspen and paper birch. The original stand pine, and little else was cut. But state laws of conifers was neither heavy nor composed of required slash burning to reduce the fire valuable species. Judged from what remains hazard, and most cutover areas eventually of it, the chief species were jack pine, white spruce, and balsam fir, with the jack pine pre- burned, often eliminating white or red pine dominant. White pine and red pine never seed trees and reproduction. Where such formed any considerable part of the stand in burning occurred, major changes in stand the great bulk of the lands. . . .-At present composition often resulted because seed there are two great types of forest, the aspen sources were altered, and no reforestation and birch, and the jack pine. The aspen and birch is the type that has succeeded the fires, work was done. Quaking aspen and paper the jack pine is mostly part of the original birch or jack pine usually replaced the red forest. and white pine in such areas because of their ability to reproduce vegetatively The area to which this statement applies (aspen and birch) or from seed on fire- includes the country from Lakes Malberg killed trees (jack pine). and Alice west to Insula and Hudson-a But unlike so much of the Lake States’ region supporting much virgin forest more pine region, settlement and land clearing than 100 yr old today. It also pertains to did not follow the logging. And most of the the vast region south of these lakes from slash fires did not spread far into the young which hundreds of thousands of cords of forests on the adjacent public domain. Thus jack pine and spruce pulpwood have been the young stands, recent burns, and scat- harvested in the past 30 yr. (His under- FIRE AND THE NATURAL ECOSYSTEM 335

standing of jack pine regeneration after fire to sixty years old.” The burns of 1894 and was certainly less than complete !) 1903-04 would have still looked barren in A slightly more sophisticated attitude to- 1908. ward fire is evidenced in the following de- H. B. Ayres, of the U.S. Geological Sur- scription of the public domain from the vey, spent much time at the turn of the ctfn- withdrawal report of S. M. Higgins (1908) : tury mapping the timber resource on the public domain in several states. His report The commercial forest in this area is much on Minnesota’s “pine region” is one of t.he broken up by burns. . For some twenty more ecologically perceptive early rlescrip- years, cruisers have gone over this land select- ing all the best descriptions. Perhaps 150,000 tions. His map showing the locations of acres of the alienated lands are covered with a merchantable timber and burned-over re- growth of white, Norway, and jack pine, gions in 1899 is the only forest map based spruce, tamarack and balsam, which will aver- on fieldwork covering the entire Canoe age a cut of 5,000 feet per acre. The bulk of Area before logging.4 The following quota- the public lands are found on burnings from one to sixty years old. . . . tions give one a feeling for the evidence of Jack pine, balsam and spruce in mixed stand fire in the ecosystem as he perceived it, comprise most of the merchantable forest. (Ayres, 1899, pp. 684-685) : White and Norway pine excepting in a few locations occur scattered throughout the stand. . much of the so-called virgin forest has Tamarack and spruce occupy the wooded been burned and is now in the various stages swamp lands. Cedar is found only in small of restocking. . Where undisturbed by quantities. cutting, the forest of today differs from that of There is a plentiful regeneration of balsam a hundred years ago only as affected directly and spruce in the mature stand. A dense re- or indirectly by fire. The oldest woods are tirr- production of jack pine, white birch, and scattered, especially where composed of young poplar follows the fire. Perhaps one-half the or middle-aged pine, having large trees scat- burns within the forest are covered with tered among it, These large trees have almost stands of this description from forty to sixty invariably been marked by fire at a dare years old, with a diameter of four to six older than the younger portion of the forest. inches. As this stand begins to thin out with Thus it is seen that fires are not a novelty age balsam and spruce regeneration comes in these old woods, but have for hundreds of in. No better guide could be had for the di- years been a prominent, factor in their history. vision of the mature forest from the forest The coming of the whites and the general dis- following the burn than the alienated and tribution of trappers and ‘couriers du bois’ public lands. . . through the woods by the Hudson Bay Com- Fire has destroyed the mature timber on pany and the American Fur Company 100 IO more than half the proposed area. The damage 140 years ago seem to have been prolific of to the soil, a clay loam, which is constantly fires, for a very large proportion of the trcrjs added to by the disintegrating rock, is not of the older uniform forests are 100 to 110 great. years of age, and must have started during t,hat period. The areas described by Higgins included This, then, is the historical background the land south of Lac LaCroix and Crooked from which the new Superior National For- Lake, and the country southwest, south, est came in 1909. As soon as staff could be and southeast of Saganaga. His descrip- assembled, first priority went to fire ran- tions can easily be visualized by one fa- miliar with these areas today. Most present ‘A map of the original forest,s of Minnesota forests date from burns in 1903-04, 1894, based on General Land Office Survey notes was 1875, 1863-4, 1854, 1822-27, and 1801-03. prepared by F. J. Marschner in 1930. It shows There are significant areas of older forest, generalized forest cover types for the Canoe but they are small in relation to these age Country and checks well with areas known to have been cut later for white and red pine, but classes. Those dating from the burns of unfortmrntely it does not show recent burns or 1875 or earlier were Higgins’ forests “forty tree sizes or ngcs (see Marschner, 1930). 336 HEINSELMAN trol. The next year, 1910, saw the last of origin. Fire scars on older trees, or his- major fires on the old public domain until torical records, were used to identify the the severe drought of 1936 and the Little actual fire year. Sioux Burn of 1971. 4. All major stands were mapped by year When the sawtimber on the alienated of origin. Airphotos and forest type maps land was cut, by 1930, the sawmills de- were used to locate stand boundaries be- pendent on northeastern Minnesota’s for- tween lakes, streams, portages, roads, and ests closed for lack of timber and the early trails. logging ended. It was not until World War 5. Fire year maps were made from the II that the maturing stands on the old pub- stand origin maps and the field evidence ; lic domain attracted a new and burgeoning these show the general burn areas for all pulpwood and crating lumber market. Since known significant fires from 1610 to 1972. then, additional land in the Canoe Area, If possible, fire-scarred trees were located aggregating some 215,000 acres gross area, and examined where needed to determine has been generally cut over for jack pine actual fire years. Most scar dates are from and spruce pulpwood, and for occasional small wedges sawn from the scarred area old red and white pine. These areas are without felling the tree, A few are from mostly part of the original public domain, cross sections cut from wind-felled trees or and were harvested under National Forest dead snags, and some are from cores taken or State timber sales. with a Swedish increment borer. Red pine, As of 1973, some 532,000 acres gross area jack pine, and northern white cedar were (land and water) of virgin landscape re- used most, because they keep scars well and main within the Boundary Waters Canoe have distinct rings. Initial ring counts were Area in large contiguous blocks uncom- made onsite with a hand lens so that the mitted to timber sales. Most of it is located stand origin maps could be drawn in the in four blocks, the largest of which encom- field. Difficult tree sections were rechecked passes about 260,000 acres (Fig. 1). The net in the laboratory. land area undisturbed by cutting is a little Stand-origin dates were obtained mostly over 415,000 acres, mostly within the origi- from cores of dominant trees of species nal public domain. known to reproduce well after fires. Ring counts were made onsite with a hand lens. FIRE HISTORY METHODS Usually two to five trees were cored for Five related techniques were used to doc- ages on each plot. Jack pine and red pine ument the dates and areas covered by past were used whenever available. Other trees fires in the virgin forests: used occasionally were white pine, black 1. A fire year chronology was developed spruce, white spruce, and aspen. Dominant through tree ring counts of sections or cores trees of fire-adapted species were used be- from fire-scarred trees, according to princi- cause the objective was to get an estimate ples first outlined by Clements (1910) and of the time of origin of the stand. Total elaborated by Spurr (1954). ages were obtained from cores taken as low 2. Historical sources and the General on the trunk as possible and extending to Land Office Survey township notes were the heart. Appropriate additions were made searched to check fire occurrences and ob- for height of boring and, if necessary, for tain firm fire dates where possible. Such distance to the heart. Dates were verified checks also tested the validity of the tree with fire scar dates from trees in the vicin- ring methods. ity when necessary and possible. 3. Stand origin dates were determined in So far, 823 stand-origin plots have been the field for the major virgin forest stands. taken. Of these, 142 include fire-scarred Ring counts were used to esbtalish years trees, and some 295 fire scars on 178 trees FIRE AND THE NATURAL ECOSYSTEM 337 were used to establish the fire chronology. thorities on the history of the area were In addition, about 100 data sets with tree interviewed to supplement field mapping ages were made available by my co-work- and other phases of the study.5 ers Drs. L. F. Ohmann and R. R. Ream. When the final stand-origin maps were Personnel of the Superior National Forest completed, a set of “fire year maps” was kindly made available all of their compart- prepared (Fig. 3). These maps include the ment stand origin data and fire maps. Maps entire l-million-acre study area referred to showing the location of all study plots are above, giving a wider base for certain fire available. statistics than would just the present virgin The final stand-origin maps (Fig. 2) forests. They show my best estimates of show stand boundaries defined either by where the larger and more severe fires natural features, such as lakes, streams, burned for each fire year. They were made and swamps, or by stand limits taken from by interconnecting the mapped limits of all 1948 cover-type maps of the Superior Na- stands that seem to have resulted from tional Forest. The latter are published, coalescent burns of the same year. Some high-quality maps based on stereoscopic in- very old burns could be traced only with terpretation of 1948 airphotos. Many fire fire scars, but most mapped burns are based boundaries were easily traced on these on combinations of stand origin and scar maps once the contrasting stand ages were evidence or on historical records, established in the field. Some independent A problem in preparing such maps is to interpretation of 1934, 1937, and 1961 air- reconstruct the paths of burns that have photos was also made. Type maps and air- since been overlapped by later fires. Stand photos were carried in the field to aid in boundaries alone suffice to map the last fire locating fire boundaries, and to build the in any area, but extrapolation is necessary stand origin maps onsite. Small stands to trace earlier fires. I believe this task waF (generally less than 5 acres) are not shown. accomplished for the larger burns since Where no data were obtained, the stand- about 1800. Between 1700 and 1800, at origin dates are extrapolations from the least the major burns are approximateIy nearest similar stands with known origins. shown. For the years before 1700, only two Transfer of stand boundaries from air- major burns are shown and their limits are photos and type maps to U.S. Geological speculative. There certainly were many Survey quadrangles was done with a pro- other burns in the 1600s. Thus, my fire year jector (Map-o-Graph). The area covered maps are a conservative estimate of the ac- by the stand-origin maps is a 1,300,000- tual fire history. As each succeeding fire acre “study area” that includes all of the sweeps the landscape, former st’ands or Canoe Area and some adjacent land. In scar-bearing trees are further obliterated. 1948, the base year for these maps, there After about 400 yr all the tree ring evi- were about 1 million acres of virgin forest dence is gone. Finally in addition to the within that area. Stand origins were large burns, there certainly were hundreds mapped for those virgin areas, even though of creeping surface fires that scarred few the original forest has since been cut in trees, if any. All traces of such fires are al- many cases. ready gone-even fires of the 20th century. Concurrent with this work, the limits of the early logging were mapped so that the 51 thank the following for their cont,ributions: fire history would not be confused with L. R. Beatty, Duluth, Minnesota (deceased) ; stand origins related to logging. This work J. A. Bola, Grand Rapids, Minnesota; G. A. Lim- produced a logging history map (Heinsel- Strom, Duluth; W. H. Magie, Duluth; E. C. Ober- holtzer, Rainier, Minnesota; S. F. Olson, Ely, man, 1969) and accurately located the Minnesota; J. W. Trygg, Ely (deceased); J. W. uncut areas. Long-time residents and au- White. Duluth; and J. F. Wolff, Duluth. FIG. 2. Stand origins on the Gillis Lake Quadrangle (U.S.G.S.), Boundary Waters Canoe Area, 1973. Forests within types date from after indicated fire year. Where stands consist of two or more age classes dating from separate fires, the years for each fire are given, with earliest fire above line. This map is an example of 45 stand origin maps covering all of the virgin forest as it existed in 1948. FIRE AND THE NATURAL ECOSYSTEM

Grand MaraiSdRl

FIQ. 3. Areas known to have been burned by significant forest fires in the Boundary Waters Canoe Area and vicinity, 1610-1972 A.D., based on stand origin maps, field evidence, and historical records. Shaded areas show general areas burned by fires of indicated years.

These points must be considered in inter- example, the General Land Office township preting the data to follow. description for T64N, R15W reads: Historical sources confirm the fire scar “Timber is very good Norway and white dates and burn areas for certain fires. For pine in the Southwest. The North half being 340 HEINSELMAN

FIGURE 3-Continued. FIRE AND THE NATURAL ECOSYSTEM 341

I - 0

d Stodv Area

J%KJRE 3-Continued. 342 HEINSELMAN

47-12 -1747

\-. $444 -i 747

&d 640 -1692

FIWJRE 3-Continued, FIRE AND THE NATURAL ECOSYSTEM 343 badly burned about twenty years ago.” body of evidence from stand origins, fire These notes were made in 1883, placing the scars, and historical data (Table 2). The fire referred to in about 1863. The south- data on known area of burns and the pro- west half of this township is shown on my portion of virgin forest burned are based maps as cut for pine between 1895 and on area estimates from the fire year maps 1915. The north and east sides show virgin for the entire l-million-acre virgin forest stands, chiefly jack pine, dating from study area as it existed in 1948. Three 1863-4, 1894, and 1910. The notes for points about the chronology should be T65N, R16W, to the northwest, were not noted: taken until May 1895. They read: “The 1. There is evidence of significant fires East two-thirds of this township is a barren somewhere in the area at l- to 8-yr inter- rock without any soil to speak of, and all vals from 1926 back to 1739. After 1926, timbers growing thereon has been killed by and before 1739, the intervals between fires the forest fires of the summer of 1894.” widen. My maps show almost all of this area to 2. Major fire years, marked by fires have supported jack pine of 1894 origin, in- burning more than 100 sq miles or more termingled with limited areas of black than 6% of the virgin forest, occurred at spruce, aspen, and red pine. The 1894 burn much longer intervals. recorded here also covered much of the ad- 3. Most of the total area burned in the joining townships to the east, southeast, period of record is accounted for by fires and north, accounting for the elimination in these major fire years. of many stands of 1863-4 origin in T64, To generalize from this record, it is help- R15, and regenerating the forests of 1894 ful to group the data by cultural history origin still present. In 1968, at the time of periods (Table 3). Effective fire cont,rol my fieldwork there, a fire scar on an 1863-4 began soon after the Superior National origin jack pine on the portage from Maude Forest was created. The last year that saw to Astrid Lakes (in Section 13) gave 1894 major burns in the virgin forests was 1910. as the year of the last fire. The “barren I therefore call the period from 1911 to rock” referred to was being logged for its 1972 the “Suppression Period.” The period 70- to 73-yr-old jack pine and spruce! of active settlement, prospecting, and tim- ber looking, spanned the years from 1868 THE FIRE HISTORY SINCE to 1910, and I term it the “Settlement Pe- 1595 A.D. riod.” The fire scar and stand origin record The stand origin and fire year maps indi- begins to fade about 1727-note the erratic cate that virtually all of the l-million-acre and widening intervals between fire years virgin forest study area was burned one to before then. Of course, such a change could several times in the 377-yr period be due to actual decreases in fire incidence 1595-1972 A.D. (This record begins in 1595 before the influence of European man. But’ because that was the approximate year of no records at all were obtained for fires be- origin of the oldest living stand found-a fore 1542 because of the absolute limit set group of red pines on Three Mile Island by the longevity of trees in the region, and in Seagull Lake.) The nearly universal oc- the limit of durability of exposed wood in currence of charcoal at the base of the litter fire-killed snags. Work by Swain (1972) in- and humus layers confirms the widespread dicates that there was as much or more fire extent of past fires. Most areas clearly prior to my record. I therefore call the pe- burned several times in the period of riod before 1727 the “Period of Fading record, but it is often possible to document Record.” only the last one to three fires. This leaves the 184 yr 1727-1911 as the The fire chronology is based on the total period of “good record” also largely un- 344 HEINSELMAN

TABLE 2 FIRE YEAR DATA FOR THE VIRGIN FORESTS OF THE BOUNDARY WATERS CANOE AREA, MINNESOTA, 1542 TO 1972 A.D.” Propor- Propor- Time Known tion of Time Known tion of since Fire area virgin since Fire area virgin Fire previous scars of forest Fire previous scars of forest year year found burns burned year year found burns burned - Num- Square Num- Square Years ber miles Percent Years ber miles Percent 1971 4 - 24 1.5 1834 4 3 2 0.1 1967 31 1 I .l 1830 1 1 - 1936 10 - 16 1.0 1829 2 2 - - 1926 I 1 - - 1827 3 4 13 .8 1925 4 - 1 .l 1824* 2 2 131 8.3 1921 1 - 1 .l 1822 7 2 75 4.7 1920 2 1 - - 1815 4 2 12 .8 1918 1 - 1 .l 1811 3 1 - - 1917 3 - 4 .3 1808 1 1 - - 1914 4 1 - - 1807 2 1 - - 1910 6 14 80 5.1 1805 2 1 - 1904 1 6 4 .3 1803 2 9 2 .l 1903 3 3 4 .3 1801* 5 5 162 10.3 1900 6 5 6 .4 1796 2 5 92 5.8 1894* 2 32 265 16.8 1794 4 1 - 1892 2 2 - - 1790 6 7 - - 1890 2 6 4 .3 1784 4 2 3 .2 1888 1 5 - - 1780 11 1 - - 1887 1 1 10 .6 1769 3 3 - - 1886 1 2 1 .l 1766 7 4 - 1885 1 1 5 .3 1759c* 4 8 312 19.7 1884 1 4 - - 1755 3 6 - - 1883 1 3 - - 1752 5 2 - - 1882 1 4 - - 1747 5 2 15 .9 1881 1 3 24 1.5 1742 3 2 - - 1880 5 7 2 .l 1739 12 4 - - 1875* 4 23 350 22.2 1727* 15 3 207 13.1 1871 3 4 10 .6 1712 15 - 9 .6 1868 4 3 - - 1697 5 1 - - 1864b* 1 50 696 44.1 1692* 11 2 103 6.5 1863 7 8 - - 1681* 33 1 154 9.7 1856 2 1 - - 1648 11 - - - 1854 8 4 60 3.8 1637 27 1 - - 1846 4 5 21 1.3 1610 15 - 9 .6 1842 8 1 - - 1595 53 - - - 1542 ? - - - 0 Basis for table is the l-million-acre virgin area defined on 1948 forest-type maps, including some areaa outside the BWCA. Some of this forest has since been cut. b 1863-64 burns cannot be separated on the ground. The total area for both years is given under 1864, which was the major year. c 1755 and 1759 burns cannot be separated in most cases. Total area for both years is given under 1759. * = “Major fire year,” burning more than 100 square miles. affected by fire control. That period can be with Good Record” (1727-1868) to examine divided into the Settlement Period the effect of increased carelessness with fire (1868-1911) and a “Presettlement Period during settlement. One measure might be FIRE AND THE NATURAL ECOSYSTEM 315

TABLE 3

FIRE YEAR INTERVALS AND BURN PERCENTS BY CULTURAL HETORY PERIODS FOR THE VIRGIN FORESTS OF THE BOUND.4RY WATERS CANOE ARM, MINNESOTA, 1542 TO 1972 A.D.&

Burned area Average ac- Average interval counted Virgin interval between for by Virgin forest between major major forest burned fire fire fire burned per Length Cultural period years year@ years* per year century of record

Years Years Percent Percent Percent. Years Total period (1542-1972) 6.1 48 82 0.43 43 430 “Suppression Period” (1911-1972) 6.1 - 0.5 5 61 “Settlement Period” (1868-1910) 2.1 ‘2 1 80 1.15 11.5 42 Presettlement period with “good” record (1727-1868) 4. 3 28 84 x2 x:! 141 Presuppression period with “good” record (1727-1910) 3.5 26 8:3 .X8 X8 1X3 Early period of “fading” record (1542-1727) 20.6 - - .lO 10 18.5

0 Basis for tabfe is the 1 million-acre virgin area defined on 1948 forest-type maps, including some areas outside the BWCA. Some of this forest has since been cut. * “Major fire years” are defined as those with burns of over 100 square miles. There were only nine such yrs: 1894, 1875, 1864, 1824, 1801, 1759, 1727, 1692, 1681.

changes in the intervals between fire years. ment rate required only 122 yr. The differ- There is such a change (Table 3), although ence between the last two periods could it is not so great as for Itasca Park, 180 again be due in part to obliteration of the miles to the West (Frissell, 1971; this sym- evidence of some earlier fires by reburns. posium). The change in the Canoe Area, Probably there was some real increase in from 4.3 yr in the Presettlement Period to both incidence and burn area in the Settle- 2.1 yr in the Settlement Period, may still ment Period, but it was not major. be due in part to a somewhat faded record Much of the burned area for both the for the earlier period. Settlement and Presettlement periods can Another measure of any effect of settle- be accounted for by just a few major fire ment would be changes in the proportion years. In the Settlement Period, the fires of the area burned in some standard time of 1875 and 1894 created 80% of the total unit. The percentage of the virgin forest burn. And in the whole Presettlement Pe- burned per century is such a measure. riod with good record, just five brief fire When this statistic is calculated for the cul- periods account for 84% of the total: tural periods, an increase in burning is indi- 1863-4,1824,1801,1755-9, and 1727 (Table cated for the Settlement Period (Table 3). 3). These facts indicate that without con- Note also the drastic reduction in burns for trol measures, large acreages were burned the Suppression Period. If the rate of burn- at rather long intervals when weather and ing recorded since 1910 were sustained, fuels combined to yield optimum burning some 2000 yr would be required to burn an conditions. The average interval between area equal to the entire study area. In con- such major fire years only varied from 21 trast, during the Settlement Period, only 87 to 28 yr among cultural periods-a differ- yr would have been required. The Presettle- ence probably related to climatic circum- 346 HEINSELMAN

TABLE 4 stances rather than human activities. The VIRGIN FOREST AREAS OF THE BOUNDARY average interval between major fire years WATERS CANOE AREA, MINNESOTA, BY for the Presuppression Period with good STAND ORIGIN YEARS, MARCH 1973a record was 26 yr, but this actually ranged (LAND AREAS ONLY) from 11 to 42 yr, and if both 1863 and 1864 Stand Cumulative are counted, two successive years even oc- origin Percent percent year Area in 1973 of total of total curred. Important fire years in common Acres with Itasca Park included 1712, 1727, 1759, 1803, 1864, and 1875 (Frissell, 1968; 1971; 1971 2032 0.5 0.5 1967 128 - .5 this symposium). 1936 7968 1.9 2.4 Perhaps more startling than any of the 1925 400 .l 2.5 statistics, however, is the simple fact that 1918 576 .l 2.6 1917 1856 .4 3.0 virtually all present virgin forest stands are 1914 32 3.0 still of postfire origin, even after 60 yr of 1910 34,000 8.2 11.2 effective fire control. That is, most of their 1904 1952 .5 11.7 1903 2368 .6 12.3 overstory elements still consist of the first 1900 512 .l 12.4 generation of trees to repopulate the burns 1894 96,944 23.2 35.6 1890 32 35.6 in question. The mosaic of age classes and 1889 256 .l 35.7 successional stages on the landscape is still 1887-8 176 .l 35.8 a fire-created pattern (Table 4). One can 1885-7 384 .l 35.9 1882 288 .l 36.0 only appreciate the intricacies of this pat- 1881 9968 2.4 38.4 tern and its fit to the landforms and water- 1875 90,614 21.8 60.2 ways by actual aerial reconnaissance or by 1871 5856 1.4 61.6 1863-4 83,600 20.1 81.7 study of the full stand-origin map set 1854 8112 2.0 83.7 (which, unfortunately, it is impractical to 1846 2656 .6 84.3 present here). But study of the stand-origin 1827 912 .2 84. B 1824 1616 .4 84.9 year classes will yield some understanding 1822 6128 1.5 86.4 of the stand age patterns and diversity cre- 1815 5200 1.3 87.7 ated by 377 yr of varying fire occurrence 1803 176 .l 87.8 1801 17,072 4.1 91.9 (Table 4). 1796 5840 1.4 93.3 There is a distinct hiatus in the age class 1784 432 .l 93.4 distribution since 1910, due to fire control. 1766 48 93.4 1755-9 12,240 2.9 96.3 And before 1900 there is a gradual decline 1747 768 .2 96.5 in year classes with time, punctuated by 1739 160 - 96.5 1727 3408 .8 97.3 irregular, but also declining, jumps in year 1712 240 .l 97.4 class areas for the major fire years. This 1692 1472 .4 97.8 pattern of year classes has been modified 1681 8560 2.0 99.8 1648 - 99.8 by man only to the extent that cutting may 1610 72 .2 100 ..o have selectively eliminated certain year 1595 16 - 100.0 classes in areas beyond the remaining vir- Tota,l 415,782 100.0 100.0 gin forests. There certainly has been selec- a Virgin areas are those ‘never logged, cleared, tive elimination of the older pine forests, roaded, etc. Essentially al2 areas have burned since for example. But this problem exists for 1595 A.D. Stand origin years are the year of the last major fire from which the overstory dates. any forest ecosystem today, and there is Many stands established prior to 1900 have been much to be learned from the available burned through one or more times without total overstory kill. For such stands the year given is the record. year of the fire from which the overstory dates, even Many individual stands exhibit a simple, though there may be significant stand elements even-aged overstory structure with one age dating from later fires. class of postfire pioneers still dominant, in- FIRE AND THE NATURAL ECOSYSTEM 347 dicating that the last fire killed virtually multiple scars. These intervals were ex- all above-ground elements of the former tremely variable, however, with some stand. This is the most common situation, stands showing repeat burns as close as 5 especially in jack pine, black spruce, and yr and others as long as 100 yr. Many of aspen forests. Fine examples are the 1864 these fires burned in the same major fire age class of these species on the north, west, years that elsewhere killed entire stands, and south shores of Lake Insula, and the while some occurred in years that are sel- 1910 burns around Amoeber, Topaz, and dom reflected in new stand origins. Where Cherry Lakes, and Lake of the Clouds. possible, the fire year maps include surface If a second major fire came only a few fire evidence, and the area of such burns years after a pervious burn, many conifers is partially reflected in Tables 2 and 4. could be eliminated, because most species Certainly there were also many light sur- do not bear cones until 20-50 yr old (jack face fires for which no evidence remains. pine and black spruce begin bearing at l@-15 yr). Reproduction might then be CLIMATIC FACTORS chiefly from the sprouters-aspen, birch, It is useful to consider the possible red maple, and oak. This may be the his- weather and climatic factors associated with tory of a large region around Wine, Hub, past fires in the Canoe Area’s virgin forests Mesaba, Dent, and Barto lakes. The last because these fires burned intact natural major fire there was in 1875, but much of stands. In contrast, the historic fires of the the area probably also burned in 1863-4. Lake States, about which so many accounts The sprouters, a few jack pines, and scat- have been written, burned largely on cut- tered spruce dominate that area today. Fir, over land carrying logging slash, or even cedar, and white and red pine are conspicu- encompassed some open hay land. This was ously rare. the case, for example, with the great Pesh- Another frequent fire-produced structure tigo, Hickley, Baudette, and Cloquet-Moose consists of two or more overstory age Lake fires discussed by Haines and Sando classes, each dating from a separate fire. (1969). Both the behavior and the ecologi- Such compound stand origins were mapped cal effects of such slash fires may greatly separately when feasible. Often the older differ from those in virgin forests because ovcrstory trees tend to be segregated into of differences in fuels and in tree seed sup- small groups, or even fair-sized groves. plies following the burn. Even most of the These are common patterns in red and region’s literature on prescribed fire con- white pine, although large, truly even-aged cerns burns in logging debris, or on semi- stands of these species are also common. open land burned to improve wildlife habi- Still another common pattern is a rather tat (Beaufait, 1962; Buckman, 1964a, b; fine-scale mosaic of two or more age Ahlgren, 1970; Johnston, 1971; Van Wag- classes. Many examples of these fire-pro- ner, 1966). The behavior, size, and ecologi- duced stand structures can be found in the cal effects of past fires in the virgin forests old red and white pine forests near Boulder depended on many interacting factors. Bay of Lac La Croix and on the islands Among the most important were season, of La Croix, Saganaga, and Seagull Lakes. preceding weather patterns, weather during In addition to the fires severe enough to the fire, vegetation types, fuel types, and introduce the new stands reflected in Table the physical landscape. 4, many surface fires in red and white pine Season is important. Given an adequate stands killed few trees. The average return climatic buildup and suitable weather, interval for fires in pine stands where some spring and fall fires burn readily and or all trees survived was 36 yr, based on spread quickly. This is because the low ring counts for 190 scars from 76 trees with vegetation is cured and the fallen needles 348 HEINSELMAN of conifers and dried leaves of deciduous some jack pine-black spruce or red pine trees and shrubs add to ground fuels. And stands where there is little seasonal change the succulent green vegetation of summer in fuels. is absent, eliminating a critical energy-ab- The ecologicai effects of these various sorbing “heat sink.” Under these condi- types of burns seem to depend on two re- tions, fires can be spectacular. “Crowning” sults of the fire: the extent of crowning and in conifers and total kill of the overstory direct overstory kill, and the depth of over large areas are possible if fuels are humus layer consumption, which affects the dry, and humidity below about 30%, and survival and regeneration of many trees, winds exceed 15-20 mph (Sand0 and shrubs, and herbs and determines seedbed Haines, 1972). But in spring, wet, frozen characteristics. soils and organic layers as well as moisture Now, what can we say about the climatic in heavy fuels usually prevent thorough circumstances associated with past fires, consumption of organic layers, snags, and and what can we therefore infer about their fallen trees. “Spring” burning conditions ecological effects? First, it is clear from the may occur between mid-April and early fire maps, fire scar dates, and climatologi- June. “Fall” conditions can develop early cal data that the total number of fires was in September or even in late August in ex- large, and that many fires did burn even ceptionally dry years. Light surface fires, in years not marked by prolonged regional causing little injury to fire-resistant red drought. For example, in the 32 yr pines, are also possible under spring or fall 1863-1894, fire scars were found for 17 yr. conditions if it is not too dry and the wind And for the whole “settlement period,” not excessive (Buckman, 1964a). 1868-1910, fires were recorded at intervals Summer fires in most vegetation types re- averaging just 2.1 yr. The climatological quire a longer climatic buildup, and more summaries for Minnesota (Martin, 1934a, severe fire weather than spring or fall fires b) document numerous short-term spring, to achieve similar intensities and rates of summer, or fall droughts at various stations spread. But in prolonged drought, evapo- during these periods. Some of these rather transpiration dries out the litter and humus brief droughts set the stage for fairly large layers, and these become part of the fuel. burns in local areas. The probability of ig- Snags, fallen trees, and other heavy fuels nition during favorable weather was cer- also dry out and may be consumed. In the tainly high, considering the activity of past, many summer fires must have been prospectors, timber cruisers, and settlers, smouldering and slow-moving as these plus the expected natural frequency of heavy fuels and organic layers burned with lightning ignitions, the retardant effect of a green undervegeta- But just 5 fire yr account for 90% of the tion. Today most such fires are extin- stand origins still present in the BWCA guished by control crews before they reach that date from the full 70 yr 1840-1910 for significant size; without control they could which some weather records are available burn large areas during prolonged droughts. and suppression was minimal. In fact, 73% Some may have held over into the fall when of all remaining virgin stands date from more rapid spread is likely. Fall fires have these same 5 yr: 1863, 1864, 1875, 1894, the potential both to move rapidly alzd to and 1910 (Table 4). Some useful insights consume heavy fuels and organic layers. can be derived from the precipitation data Some nearly pure conifer stands with for these years (Table 5). only lichen, moss, and heath-shrub under- In 1863, Beaver Bay, Fort Ripley, and vegetation may burn much the same in St. Paul all recorded very light precipita- spring, summer, or fall. I am thinking here tion from April until August. Thereafter, of black spruce-feathermoss types and rainfall was probably sufficient to check or FIRE AND THE NATURAL ECOSYSTEM 319

TABLE 5

PRECIPITATION AT SELECTED MINNESOTA STATIONS FOR SOME IMPORTANT FIKX YE.\RS” (Inches) -~__ .ln- Fire rlWd year Station April May June July Aug Sept. art. Total

1854 Fort Ripley .97 4.34 3.68 (i’2 1.69 4.49 .!)I St. Paul 2.51 4.30 3.31 3.92 1 .7:, 6.55 1.23 ‘26 *5!) I_-- 1863 Beaver Bay 1.01 1.9.5 1.16 4.35 2.76 2.44 Fort Ripley .61 1.89 *2x .60 .i. 17 4.32 1.97 St. Paul .80 2.87 .02 63 3.17 1.23 1.44 I 5 7 7 1864 Beaver Bay .25 1.65 .29 3.16 3.28 2.32 2.18 Fort Ripley 1.35 .92 .90 4.X2 1.37 .90 St. Paul 1.10 .47 1.62 4.14 2.00 1.14 ---1 .60 -~~-.~~15.5:< - 1875 Breckenridge 1.07 3.8.5 4.95 .70 3.31 1.80 :57 Duluth 2.82 2.45 1.84 .47 6.19 3.77 2.60 27. o:< Fort Ripley 1.9;5 4.40 2 33 3 !I9 3 ,i9 3.O!i .36 .- St. Paul 2.27 3.06 4.38 .x2 8.74 2.16 1.56 30 66 1894 Duluth 5.83 5.62 1.89 92 1 .ou 2.08 4.99 31 (70 Virginia 4.75 3.89 4.98 1.67 94 4.64 5.69 34.7:< Winnibigoshish 3.92 2.72 3.97 .49 .XY 2. -50 3.43 2:i. 50 St. Paul 4.39 6.63 1.51 .13 36 1.82 4.49 25.80 ..____--- .-_. 1910 Duluth 1.40 1.18 .ll 3.x9 2.41 4.20 .81 18.11 Virginia 2.67 1.41 .35 4.60 1.04 3 83 1.41 18.39 Winnibigoshish 2.10 1.90 .84 3. 39 :i3 4.10 1.10 Ii.16 St. Paul 59 1.76 .91 99 .98 1.77 75 10.21 1936 Duluth 2.6.5 2.76 93 63 1 93 I .48 1 28-~.~-..~-- 20.9 3 Grand Marais 1.95 4.59 1.72 1.09 2.18 I .84 1. 30 24.72 Tower 1.30 3.19 1.68 2.00 3 09 2 32 .96 21.50 Virginia 1.17 3.00 1.6.5 1. .53 2.95 1.88 x2 2!1 3 1 Winnibigoshish -1.05 1.91 2.37 59 2.28 1.7.: .I7 1 3 3 5 Minneapolis 1.48 2.25 2.29 .ll 3.48 .7x 69 18.47 --__ -__.- ._____- ._. _ Period of record Station Normal precipitation

Years -59 Duluth 2.03 3.24 4.14 3 us 3 1.5 3 -53 2.36 2x.42 42 Font Ripley 1.79 2.90 3.98 2.86 2.83 2.48 1.49 21.57 27 Grand Marais 1.50 2.01 3.00 2.91 2.83 3.43 2.25 24.71 38 Minneapolis 1.9.5 3.40 4.27 3.44 3.26 3.40 2.19 27.31 !I:‘, St. Paul 2.29 3.30 4.13 3.38 3.37 3.21 2.00 27.17 19 Tower 1.60 3.00 4.03 3.50 3.80 3.88 2.37 27.38 40 Virginia 1.60 2.81 3.70 3.64 3.57 3..58 2.11 26.04 40 Winnibigoshish 1.73 2.94 3.64 3.36 3. 7.5 2.82 1.76 24 .04 -. __- a Source: Climatological summaries, Minnesota, Martin 1934a, b; and unpublished data in historical files, Minnesota State Climatologist, Earl L. Kuehnast, St. Paul, Minn. (Personal communication) for Fort Ripley and Beaver Bay. extinguish most fires. But the following Ripley and St. Paul. The fires of these 2 spring (1864) again little rain fell, the yr cannot be separated on the ground, but drought persisting until July, returning they consumed the forests thoroughly in again in August and September at Fort most areas where they burned. Remnants 350 HEINSELMAN of former stands are not common, and large speaks of “the fire of two summers.” At areas are know clothed with even-aged jack Itasca Park, 180 miles west, first Spurr pine, spruce, aspen-birch, and sometimes (1954) and later Frissell (1968, 1971, and red and white pine stands that reproduced this symposium) identified large areas in their wake. The region around Lake In- burned by 1864 fires. Spurr gives the year sula is an example familiar to present-day as 1865, but the subsequent more extensive visitors. studies of Frissell confirm 1864. Grange The weather records suggest that, the (1965) reports l,OOO,OOO acres burned by fires of 1863 came in the spring or early 1864 fires in Wisconsin, summer, while the 1864 fires might have The most remote record of 1884 fires burned almost the whole season, except per- comes from the pioneering study of Fred- haps for a few weeks in July. At Fort Rip- erick E. Clements at Estes Park, Colorado ley, the weather chart, for June 1863 (Clements, 1910). He concluded that the notes : “The drought is very severe, the burns of 1864 were the most extensive of grass upon the prairie is nearly or quite any in his study area (just as I have, 60 dried. The Mississippi River at the point yr later and 1000 miles to the northeast !) . is lower than it were ever known before.” This work, incidentally, employed essen- (Unpublished records, courtesy of Minne- tially the same techniques for dating and sota State Climatologist, E. L. Kuehnast, delimiting fires that Frissell and I have St. Paul, Minn.) used. An idea of the regional extent of the I conclude from the foregoing that the 1863-4 droughts can be gleaned from scat- droughts of 1863 and 1864 were major cli- tered historical records and from other fire matic anomalies, probably subcontinental studies similar to mine. For example, notes in extent. The first fires may have occurred from a Samuel Taylor’s journal at Fort in May and June of 1863, under spring fire Garry, (now Winnipeg) Manitoba confirm conditions. A complete overstory kill, but the severity of the 1863-64 droughts in that little consumption of organic layers or region, some 300 miles northwest of the heavy fuels, might have then occurred. But Canoe Area. On July 1, 1863, Taylor as the drought intensified in July of 1863 wrote: I‘. . . a dry hot day this is the dry- and again in late June, July, August, and est summer that anyone can remember the September of 1864, many summer and fall wheat looks short and thin. . . .” And on burns probably occurred. Some of these September 25, 1863, ‘I. . . only 9 bushels may have been of the slow-moving, smoul- (potatoes) from 9 bushels of cut seed owing dering type in midsummer, others fast- to dry weather all summer. . . .” On Au- moving fall burns. Without suppression, gust 9, 1864, he writes: “. . . the fire is many of the early summer fires probably burning the hay on all directions the very survived the rains of July 1864, and fanned earth is burning the like is never been out over adjacent terrain in late summer known. . . .” and on August 14th “. . . a and fall. Such a sequence fits well with the terrible squall of wind . . . like to blind mapped extent, of the 1864 burns as they people with dust. . . .” (From the original are now known (Fig. 3). At, the same time journal, courtesy of the Laboratory of large areas of forest throughout northern Anthropology, University of Manitoba, Wisconsin, Minnesota, and adjacent On- Winnipeg.) tario and Manitoba were probably involved On the Cutfoot Sioux Experimental For- in fires. Such major fire periods as this est, about 100 miles west of the Canoe may have occurred only once in a century Area, there are extensive even-aged red or two. But when they came, very large pine (and formerly jack pine) stands dat- areas of forest were transformed from ad- ing from 18634 fires, The local lore there vanced successional stages or maturing FIRE AND THE NATURAL ECOYBSTEM X?l pioneer stands to new postfire plant com- The actual dates for the fires in the Canoe munities. In the Canoe Country, at least Area have not been discovered, but it is 44% of the million-acre virgin forest study likely that there were spring, summer, and area became involved in the burns of these fall burns. Several separate fires were 2 yr (Table 2). clearly involved (Fig. 3). Some probably The next earlier period when a similar began as slash fires on logging operations climatic and fire sequence may have oc- and spread into adjacent virgin stands. curred was 1755-1759-more than a cen- The last major drought year marked by tury before. There are no climatic data and large fires in the virgin forests of the Canoe no eyewitness reports. But the silent testi- Area was 1936. Precipitation was far below mony of many stands of even-aged forest normal all summer for most northern dating from these years, and an abundance Minnesota Stations (Table 5), and this of fire scars still identify some of those year was the last of several successive years burns. The forest regeneration that fol- of subnormal precipitation. Hundreds of lowed these fires must have been similar man-caused and lightning-caused fires oc- to that which occupied the 1863-64 burns curred in the Canoe Country, but only because even today there are large areas three burned large acreages of virgin forest where 215-yr-old jack pines dot the land- within the present BWCA. These were the scape within the 1755-59 burns. Frost Lake and Cherokee Lake fires, and The 1875 fires must have burned in July, the Canadian Outbreak. They occurred in as this is the only month that shows up *July and August and were lightning-caused. consistently in the precipitation records as All three were heavily manned by Forest a drought period (Table 5). No actual re- Service and Civilian Conservation Corps ports of these fires have been found. The control teams and are covered by detailed 1894 fires could have burned any time be- reports and maps. tween late June and September, as the cli- The Cherokee Fire burned from July 12 matic data indicate drought persisting most to 15, most of the burn occurring on July of the summer that year. All stations cited 13. That day the fire advanced 2.5 miles show severe rainfall deficits for July and in 10 hr, burning about 2500 acres. The air August. The great Hinckley Fire occurred temperature was about 9OoF (32OC), the on September 1, 1894, about 150 miles relative humidity 20%, and wind velocity south of the Canoe Area. General Land 15-30 mph from the west and northwest,. Office Survey notes (quoted earlier) speak The total area burned was 3200 acres. A of “the fires of the summer of 1894” in the brief, heavy rain during the night of July Canoe Country. Most of these fires prob- 14 aided suppression by a crew of more ably burned in July, August, or early Sep- than 600 men. About half of the burn was tember because general rains did occur in 1727 origin mixed conifer and deciduous later in September. forest ; the other half was in 90-yr-old jack The 1910 fires could have burned any- pine of 1846 origin. Much dead balsam fir, time between May and early October, al- killed by a spruce-budworm outbreak 10-20 though good rains were received at most yr earlier, augmented the fuels. stations in September. The precipitation at The Frost Lake Fire burned from August St. Paul in 1910 was the least ever recorded 12 to 22, consuming about 3500 acres of to the present. Some northern Minnesota mixed conifer-deciduous forest, mostly of Stations recorded fair rains in July, but the 1727 origin. Much of the burn involved in- drought returned, and the historic Baudette sect-killed and blown-down balsam fir and Fire occurred on October 10. This was also spruce, probably resulting from a spruce- the year of the great Idaho and Montana budworm outbreak early in the century. fires-implying a subcontinental drought, This fire made its largest advances on sev- 352 HEINSELMAN era1 fronts on August 17 and 18, with strong the snow had been gone only about 3 wk, southwest and northwest winds. The longest but there had been almost no precipitation single-day runs were between 1.5 and 2 since the snow left. Green-up of the vegeta- miles. A prolonged soaking rain on August tion had not yet occurred, and rapid spread 22 aided 800 men in final control. was also aided by several large meadows The Canadian Outbreak fires burned and open cutover areas. Most of the burn from August 3 to 9 on the American side occurred on May 14 between 2:00 PM and of the international boundary near North, midnight. The maximum advance during South, and Rose Lakes. On the Canadian this lo-hr period was about 7 miles. The side it was necessary to patrol this fire until gross area encompassed by this first day’s October 15. Most of the burn was in On- run was about 8000 acres. During this run tario; some of it in recent logging slash. In the air temperature was near 76OF (24OC), total, about 900 acres were burned on the the relative humidity near 15%, and the U.S. side, some in spruce-fir-birch forest winds southwest to northwest at 15-20 mph, that had much dead material on the with gusts to 30 mph (Sand0 and Haines, ground, and some in 1681 and 1755-1759 1972). Spotting occurred up to three- origin red and white pine, with a fir-spruce fourths of a mile ahead of the main flame understory. On August 3 these fires spotted front. Tree lichens (Usnea and Ale&or&z) across Rose Lake on a strong northwest growing on budworm-killed fir and spruce wind. Most of the other major advances of facilitated spotting-both as a source of these fires on the American side were made flying brands and as sites for quick ignition. on strong west, northwest, or north winds Consumption of organic layers was not (south or southwest winds drove these fires deep, and the root systems of most trees, toward Canada). shrubs, and herbs capable of vegetative re- The severe summer drought that made production by sprouting were still viable all of these 1936 burns possible had two im- after the burn (Books, 1972). Rain (and portant effects: First, even today it is obvi- later snow) commenced on May 17, greatly ous that consumption of organic layers and aiding 500 firefighters in control and dead and down timber was thorough. And mop-up. second, in many areas the root systems of In comparing what is known of the cli- plants that reproduce by sprouting may matic circumstances that accompanied past have been consumed. major fire years with the detailed records The Little Sioux Fire of May 14-17, for 1936 and 1971, one fact stands out. The 1971, is the most recent large burn in the major fire years for which climatic data are Canoe Country. It burned a gross area of available were all characterized by summer about 15,000 acres, but only about 2000 droughts, or droughts that extended from acres were in virgin forest within the Canoe summer into fall. This was the case for Area. Much of the fire was in logging debris 1863, 1864, 1875, 1894, and 1910. These and budworm-killed fir left after timbering years had drought patterns similar to 1936, operations in mixed conifer and jack pine not 1971. Severe spring droughts also oc- stands of 1755 and 1864 origin. The virgin curred, notably in 1863, 1864, and 1910. stands burned included jack pine, as- Possibly the major atmospheric circulation pen-birch-fir, and fir-birch stands of 1864 patterns and other climatic variables asso- origin, and two areas of 1755 or 1681 origin ciated with these subcontinental droughts red and white pine with a fir-spruce under- were all similar. When the underlying at- story. Budworm-killed fir was a major fuel mospheric factors causing such extensive in all virgin stands. This fire, unlike the droughts are better known, we may be able three just described, was a spring burn. to identify the weather factors that lead to Snowfall that winter had been heavy and major regional fire years, FIRE AND THE NATURAL ECOSYSTEkl

IGNITION SOURCES AND FUEL INTERACTIONS

Lightning is the only significant ignition __----.-_-- - - PVr- source not man-related. It may well be Light- vent sufficient to have produced the amount of plan- ning- light- fire recorded from 1595 until 1910 (when All caused rauscd ning- Mont,h fires fires fires caused control began), even though we know many - ~__ --~-...-. .- fires were actually man-caused. Thunder- Num- Num- NUUl- Per- storms occur about 25 days per year over her brr her (8cant northeastern Minnesota (USDA, 1941; April 3; 4 0 0 Komarek, 1964) chiefly between April and May xl ,i I ,1 October. They are usually more frequent June 6% 56 1’2 1x July 103 71 :Si! 3 I in midsummer than in spring or fall, al- August 123 76 47 :;5 though yearly patterns vary greatly. Duff September 58 4x 10 Ii layers and dry snags are often ignited by October 20 1 a 7 :13 Total 411 208 1 1 :: “7 lightning strikes, but most such fires are ex- - tinguished by rains that accompany the a Data from records of the Superior National storm. Occasional storms with little or no Forest, compiled by Rodney W. Sando, University precipitation occur, however, and if they of Minnesota, 1972 (unpublished summary, per- coincide with drouth, forest fires may result. sonal communication). Nearly all lightning fires are now quickly extinguished by control crews, but the fire all fires in the northwestern Canadian taiga records of the Superior National Forest still were lightning-caused from 1961 through show the potential for lightning ignitions 1964. And in the Alaskan interior, light,ning (Table 6). Most lightning fires occur in accounted for 35% of the ignitions, but July and August, although some have been 72% of the area burned from 1960 to 1969 recorded for all months May through Oc- (Barney, 1971i. tober. While the proportion of fires caused In the Canoe Area man was simply an by lightning is now low, it must be remem- added source of ignitions until about 1910. bered that the Canoe Area hosts some Thereafter, he also became a factor in lim- 160,000 recreational visits annually, and iting burn size. The relevant question, then, most campers cook with open fires. Several is how much burning would have taken large logging operations were also sources place prior to 1910 if only lightning igni- of man-caused fires. Thus the potential for tions had occurred? A direct answer is un- man-caused ignitions is probably greater obtainable. But given only lightning igni- now than in the Voyageurs’ era, and per- tions, the burn patterns would result from haps greater than in the settlement era. It interactions between, (1) the number, tim- must be far greater than in pre-Columbian ing, and locations of ignitions, (2) climatic times, when the human population was variations, (3) weather during fires, and much lower. Viewed in this context, light- (4) the mosaic of fuels on the landscape. ning is still a surprisingIy important cause The natural fuels mosaic is controlled by of fire. vegetation types, stand age ciasses, and By comparison, in the Canadian and successional stages-but these are them- Alaskan boreal forests there are only 3-10 selves a function of past burn patterns. days with thunderstorms annually, but Man changed these patterns only insofar lightning is a relatively more important as his ignitions caused burns that would not cause of fires becausethe human population otherwise have occurred. is lower. Scatter (1971) states that 72% of To understand man’s possible role in in- 354 HEINSELMAN creasing natural fire we must, then, con- ing “ladder fuels” capable of carrying fire sider the interactions between vegetation into the crowns of the overstory. These un- types, stand ages, successional stages, fuels, derstory species have very flammable climatic and weather patterns, and igni- foliage. tions. Mutch (1970) argues that fire-de- 4. Within 100-150 yr after fire balsam pendent vegetation types burn with a non- fir may increase enough to sustain a random periodicity regulated by their spruce-budworm outbreak, especially if the flammability, which in turn is linked to in- burns are large, because old trees would bred regeneration adaptations requiring then cover large areas (see Van Raalte, fire. This general hypothesis has merit, and 1972). Once fir mortality from defoliations it may help us understand the interactions commences, dead fir adds to fuels. These alluded to above for the Canoe Area. My fuels are augmented by tree lichens, which version of this theory is simply that many become tinder for spot fires. Stand openings factors linked to stand maturation and permit increased solar isolation, rapid dry- senescence increase the probability that ing of fuels, and increased air movement older stands will burn. Let me outline how (Haines and Sando, 1972). these factors operate: 5. As the pioneer forest ages, the first- 1. Total above-ground biomass in living generation overstory trees become more plants increases with stand age, up to some susceptible to wind breakage and uproot- maximum for each first generation postfire ing. Individuals are felled or, rarely, most forest type (see Loucks, 1970; Hegyi, of the stand is blown down. Such trees are 1972). Some living stand components are an additional source of dead wood (a par- potential fuel, especially in crown fires tial explanation for 2, above). (foliage, branches, portions of the bark of 6. Many pioneer stands contain paper trees; shrubs, some herbs, most mosses and birch, which develops loose scrolls and lichens). The time after fire at which bio- strips of highly flammable bark 50-150 yr mass peaks varies with forest type, but for after establishment. Wind blown birch bark most types in the Canoe Area it is at least causes spot fires. 100 yr. For stands with red and white pine 7. Tree diseases such as the heart-rotting as dominants it may be 150-250 yr. fungi, and plant parasites such as black 2. There is a general relation between spruce dwarf-mistletoe increase with stand time since fire and dry weight of dead age, eventually causing direct mortality wood. Such fuel is initially high in succes- and increased susceptibility of living trees sions following crown fires (snags from the to fire (relates to 2, above). fire-killed stand), but this first peak comes 8. There is a gradual accumulation of when other fuels are low, and the fuel-bed litter, duff, and humus on the forest floor arrangement is not conducive to fire spread as postfire forests mature. Rough measure- (the snags are standing and widely ments during the present study indicate spaced). During midlife of the new stand that accumulations of l-3 in. are usual this fuel decreases, probably reaching a within the first 100 yr after fire. Local site, minimum at 30-70 yr after fire. A resur- overstory, and groundcover factors control gence of dead wood occurs as the first-gen- depth and actual dry weight values. On up- eration trees begin to deteriorate and die land sites accumulations of 3-5 in. or more at 100-300 yr after fire. Here fuel-bed ar- are possible beneath mixed-conifer stands rangement is better, and other fuels also at- 250-350 yr after fire. On 0001 north-facing tain maxima. lower slopes, seepages, and bog margins, 3. Within 50-100 yr after fire an under- indefinite accumulation and peat formation story of fir, spruce, or cedar commonly de- may occur. During severe drought these or- velops beneath the pioneer forest, introduc- ganic layers become fuel. FIRE AND THE NATURAL ECOSYSTEM :kj;i

All of these factors and others tend to TORS, but certainly fires did occur in all increase available fuels and the flammabil- possible fire seasons. ity of stands with advancing age. And a gradual increase in total dry matter per PALEOECOLOGICAL EVIDENCE unit area on the landscape seems to occur OF FIRE up to at least 200-300 yr after fire. Quanti- Charcoal fragments and fossil evidenc.e tative estimates of the more important fac- found in lake sediments, peat bogs, and tors could now be made by actual field glacial deposits indicate that’ fire was a sampling, using the stand-origin maps as major factor in northern Minnesota’s forest the basis for samples from a full range of ecosystems long before the arrival of Euro- postfire stand age classes and community pean man. Lake of the Clouds, a small, types. Unfortunately such data are not yet deep lake in the largest virgin region of tht) in hand. Certainly these correlations of Canoe Area, cont.ains annually laminated fuels with stand age are not simple, because bottom muds that provide a detailed record some dense conifer stands become highly of vegetation and fire over postglacial time. flammable at 30-50 yr of age (Sand0 and Craig (1972) prepared a pollen diagram Eel Wick, 1972). But it seems clear that the this lake showing the vegetational history probability of ignition and of a high inten- since deglaciation, time-controlled by 9375 sity fire generally increases as first genera- varves in the upper sediment, and Swain tion stands reach maturity and senescence. (1972, and this symposium) related fire frr- With time the probability of a lightning- quency to this same chronology by counting caused ignition approaches certainty. Once the charcoal fragments in Craig’s sediment, a significant fire occurs, the fuels are re- samples. duced, successions begin anew, and fuel Briefly, the history at Lake of the Clouds patterns on the landscape are reordered. is this: After deglaciation a sparse vegeta- The burns themselves help control the mo- tion producing little pollen existed for a saic. (See also Heinselman, 1970b; Dodge, time, followed by a period of tundra-like 1972.) vegetation. A boreal spruce forest then en- My thesis, then, is that it was these fuel tered from the south as the result of major factors related to vegetation type, stand climatic change. That forest was transitory, age, and successional stage-interacting however, and with continued climatic with climat’ic oscillations-that regulated amelioration, jack and perhaps red pine re- the pattern of burns in primeval times. placed spruce as the dominants about 9200 Lightning and man were both sources of ig- y.a. Paper birch and alder arrived about nition, but it mattered little which was the 8300 y.a., and 6700-7000 y.a. whit.e pine ap- actual cause. Fuels and weather determined peared with the onset of the postglacial cli- whether a significant fire would occur, and matic optimum. Charcoal levels remain lightning alone was an adequate source of high until about 6000 y.a., when a decline ignitions to guarantee that all flammable seems to coincide with increases in white stands would eventually burn. Man’s best pine and decreases in jack and red pines. opportunity to burn forests when lightning White pine then flourished as a major dom- ignition was less probable must have come inant until about 3000 y.a. Charcoal lrlvels in the spring. But even then lightning igni- fluctuated but were generally lower during tions do occur. And if man fired a stand this time. Beginning about 3000 y.a. a re- in the spring, he simply substituted a spring turn to moister and perhaps cooler condi- fire for a summer or fall fire that eventually tions led to decreases in white pine and to would occur in any case. The ecological increases in spruce, jack pine, and other effects of spring fires may sometimes be elements to present levels. From about 3000 different, as noted under CLIMATIC FAC- to 1200 y.a. decreased charcoal levels cor- 356 HEINSELMAN respond with increases in northern white the Canoe Area, charcoal was found in cedar and some decreases in pine-logical many peat strata, the oldest having 14C trends, inasmuch as cedar is fire-sensitive ages of about 8000 y.a. (Heinselman, 197Oc). and the pines are fire-dependent. This en- The oldest positive evidence of fire in tire sequence fits well with the previously Minnesota comes from charcoal finds in known glacial and vegetational history of glacial drift. Rosendahl (1948) reported northeastern Minnesota (Wright, 1968 ; charcoal associated with remains of Picea Wright and Watts, 1969)) and adds a per- mariana, P. gluca, Larix laricina, Pinus spective on the role of fire. banksiana, Populus, and many shrub and Swain (1972, and this symposium) also groundlayer species. This material, found prepared much more detailed charcoal and in a well boring near Bronson in northwest- pollen curves for the last 1000 yr, based on ern Minnesota, has a ‘“C age of more than close-interval sampling of the upper layers 36,000 yr. A second find, from near the base of laminated sediment in Lake of the of four Pleistocene drifts, was recovered in Clouds. These studies indicate more fire in excavations for an iron mine at Bovey in the ecosystem between 1000 A.D. and about northcentral Minnesota (Heinselman and 1420 A.D. than for most periods since. Roe, 1963). A 14C date (from wood) indi- Charcoal maxima occur near 1300 and 1400 cated dead carbon-placing the time before A.D., before any settlements of European 38,000 y.a. Charred wood was found asso- man on the continent. A period of reduced ciated with two closed cones of jack pine, fire then persists until about 1670 A.D. The several open cones of black spruce, and next 80 yr, from 1670 to about 1750, show wood identified as Picea, Larix, Abies, a strong charcoal peak, followed by an er- Pinus, Populus, and Vaccinium-all genera ratic decline to very low levels in the up- still present. Both sites evidently predate permost sediment. The vegetation reflected early man in America (see Irving and by the pollen curves was relatively stable Harington, 1973 ; Martin, 1973). There is over this lOOO-yr period, showing only also some pollen evidence for jack pine in short-term shifts in the relative abundance the Sangamon interglacial period, about of species following major fire episodes. 100,000 y.a. (Yeatman, 1967). Thus fire Both the charcoal and pollen curves ap- and some of the present fire-dependent parently record a mixture of regional and forest dominants-at least jack pine, pop- local contributions, because the charcoal lars, and black spruce-were associated in counts are of very small, wind-borne frag- Minnesota before man was a possible ments. Thus a precise record of fires at source of ignition. Jack pine apparently Lake of the Clouds itself has not yet been evolved its cone serotiny in a lightning-fire achieved, but the general pattern of past environment in Miocene, Pliocene, or early fires in the region is clear. My fire chronol- Pleistocene time, 1 million-20 million y.a. ogy for the last 400 yr evidently covers a (Mirov, 1967; Yeatman, 1967). period that saw somewhat less fire that oc- curred in several long periods before the in- PHYSIOGRAPHIC FACTORS fluence of European man in North America. Stratigraphic studies of peat bogs also re- Study of the fire year maps, 1948 forest veal evidence of past fires in northeastern type maps, and stand-origin maps suggests Minnesota. Several charcoal layers in the interactions between historic fire patterns, Lindford Peatland, 80 miles west of the vegetation, and several physiographic fac- Canoe Area, date fires only a few hundred tors. These factors are: years ago to near 3000 y.a. (Heinselman, 1. Location, size, shape, and compass 1963). And in the Lake Agassiz Peatlands alignment of lakes, and the abundance of Natural Area, about 70 miles southwest of islands in them. FIRE AND THE NATURAL ECOSYSTEM 357

2. Location, size, shape, and alignment a general west-to-east axis. They were less of streams. often effective in preventing west-to-east 3. Location, size, shape, and alignment movements, even when aligned on a of wetlands (forested swamps and peat- north-south axis across the fire’s path. lands, marshes, muskegs, etc.). 3. The art’as burned most frequently or 4. Location, size, relative elevation, and intensely are large upland ridges and ridge alignment of bedrock ridges and glacial complexes, distant from or west of natural landforms. firebreaks. Jack pine, black spruce, aspen, 5. Location, size, relative depth, and birch, and other sprout hardwoods often alignment of fault lines, valleys, troughs, dominate such areas today. Long west-east and other lowlands. ridges often burned full-length, serving as 6. Soil textures and rockiness. firepaths for eastward spread of major fires. These landscape features apparently are 4. The areas burned least frequently or linked to past fire movements because they intensely are swamps, valleys, ravines, the re1at.e to either natural firebreaks or fire- lower slopes of high ridges (especially east paths. Some, such as ridges, valleys, wet- or northeast faces), islands, and the east! lands, and soil texture, may also relate to north, northeast, or southeast sides of large fuels through their influence on slope, as- lakes or streams-especially those with pect, soil moisture, soil depth, fertility, and much open water in relation to island area. other factors that affect productivity and White pine, red pine, white spruce, nort,hcrn community composition. Alignment of white cedar, black ash, elm, and fir are landforms and water bodies evidently is relatively more abundant on such sit’es. important because tie weather usually Any site on the favorable side of a possible came with west, southwest, or northwest firebreak is more likely to support these winds that pushed fires along firepaths species. The more effective the barrier, the leading eastward. Even weak fire barriers higher the probabilit’y. often stopped north-south spread of fires, The relation of white and red pine to fire- or spread from an easterly bearing. But barriers is especially interesting. Both often only very large and effective barriers often reproduce well after fire, and are really blocked spread to the east, southeast, or fire-dependent. Both are resistant to mod- northeast. These statements are based on erate surface fires when mature, but can be careful study of the stand-origin maps, but killed by severe crown fires. Both have only each fire was a special case, and there were intermittent seed crops and nonpersistent, many exceptions. Yet 400 yrs of fire pat- open cones, although white pine is the more terning left a clear record of the prevailing prolific seeder. Neither grows well in heavy conditions, and this is what one seestoday. shade, alt8hough white pine is the more Based on such map study, and on many shade-tolerant. Both seed-in well on bare field observations, I make the following soil or thin organic layers, but white pine generalizations : can survive on thicker organic layers than 1. The firebreaks most often effective red. These characteristics imply a need for were large lakes, especially those with few the disturbance regime provided by combi- or widely spaced islands. Small or long-nar- nations of occasional light surface fires and row lakes aligned east-west often checked more severe fires only at long intervals. ,4n north-south spread, but it was chiefly the occasional surface fire would keep down large and wide lakes that checked west to organic layers and understory trees, thus east spread. preventing fires severe enough to kill the 2. Streams, wetlands, valleys, and overstory. If a more severe fire then came troughs frequently checked fire spread, es- along once every 100-300 yr, this would be pecially to the north or south if aligned on adequate to create the necessary stand 358 HEINSELMAN openings and occasional killed-out areas for this concept. By this I mean simply the regeneration. This is the kind of fire regime average number of years required in nature that prevailed where many stands of these to burn-over and reproduce an area equal pines occur today. Their most common to the total area under consideration. Such location is on islands, or on the east, north, a statistic can be calculated with some pre- northeast, or southeast sides of lakes, cision only if fire history maps are avail- streams, swamps, or valleys. Fires in such able for a relatively long period when man locations are often ignited as spot-fires, and had little direct effect on the system. But they burn as backfires moving against even if only crude approximations can be westerly winds-creeping downslope to- obtained, such estimates have value be- ward the lakeshore or swamp edge. The cause they permit direct comparisons be- known locations of major stands of old pine tween ecosystems for scientific purposes that were cut in the early logging era also and provide guidelines for fire management agree with this pattern. Many old red and programs. white pine stands do bear scars from the For the Canoe Area the natural fire rota- surface fires that burned through them, and tion is about 100 yr. This is the average many of these fires occurred in the same time required to burn and reproduce an major fire years that elsewhere killed for- area equivalent to the whole l-million-acre ests over extensive areas, bringing in whole virgin forest study area for the period new generations of trees. This suggests that 1727-1910, allowing for some lost record in it was the physiographic location of such the early years (Table 3). In addition to stands that ameliorated fire intensity and the fires involved in this statistic, there made the survival and regeneration of red were many surface fires that merely scarred and white pine possible. The average inter- occasional red and white pines, and un- val between fire scars in such stands is 36 doubtedly still more that left no trace. Sur- yr. face fires that failed to introduce a new Northern white cedar is very fire-sensi- generation were most common in red and tive, and has almost literally been driven white pine stands, because all other trees to the lakeshores by fire. It is so uncommon are so fire-sensitive that most fires prob- on uplands that it is often considered a spe- ably killed enough trees to regenerate the cies requiring high soil moisture and mobile area. groundwater. But the proof that it can cope Reducing all this fire history to a single with dry sites is that it is sometimes abun- statistic such as the lOO-yr natural fire ro- dant on ridges on certain islands and other tation may obscure the wide actual vari- sites where fires have been infrequent. ability in stand life, both between and Many lakeshores are lined with cedars, but within community types. Let me hasten to the cedar fringe is usually narrow. A little correct any false impressions. It is a valid detective work will quickly reveal the rea- measure of fire’s role in the total system, son: many old cedars are fire-scarred on but each community type probably also the side away from the lake, and the had a characteristic average fire rotation younger trees spreading inland usually date of its own. I lack the data to calculate such from after the last fire. statistics, but I obtained a feeling for the situation in the field. THE NATURAL FIRE ROTATION Red and white pine stands often survive We need a measure of the amount of fire intact 200-300 yr, with a possible maximum in ecosystems that defines the average rate for single trees or small groups of 400-500 at which new forest generations were estab- yr. In nature, average stand life was prob- lished in natural fire-dependent systems. I ably 150-250 yr. The oldest red pine bored propose the term Natural Fire Rotation for in my study is now 378 yr old. Older white FIRE AND THE NATURAL ECOSYSTEM 359 pines may have been encountered, but all can be carried into the overstory. If pro- were too rotten to yield full cores. Many tected from fire, white spruce probably has jack pine stands loo-215 yr old have un- a maximum longevity of at least 300 yr, doubtedly escaped fire in the last 60 yr be- and white cedar 400-600 yr or more. Bal- cause of fire-control measures. Overstory sam fir rarely survives more than 200 yr. mortality and the invasion of fir-spruce Hopefully, it is clear from this discussion understories is commonly well advanced at that great variability in fire patterns artu- 100-115 yr. I would guess that many jack ally produced the fire records that add up pine stands formerly burned 50-100 yr from to a neat’ lOO-yr average fire rotation. What~ establishment. The oldest individual jack really happened over a given century on pines bored were approximately 245 yr old. any large landscape unit was the result of Aspen-birch types evidently had average an extraordinarily complex series of inter- fire rotations similar to jack pine types, be- actions between lightning and man-caused cause they were almost always of the same ignitions, fuel patterns, vegetation types, age class in given areas. Few cores were physiographic factors, past burn patterns, taken because rings are difficult to count and the vagaries of weather, season of the in old trees, but many individual quaking year, and climatic buildup for each specific aspens undoubtedly attain ages of 150-200 fire. yr. Paper birch has a maximum longevity of at least 250 yr. Black spruce is often a SUCCESSION, DIVERSITY, AND postfire pioneer, both on uplands and peat- STABILITY IN RELATION TO FIRE lands. On uplands its natural fire rotation Much ecological literature indicates that seems to have been close to that for jack succession often leads to increased species pine, and individual trees have lived at diversity and stability in plant communi- least 227 yr (the oldest upland specimen ties (see Krebs, 1972; Whittaker, 1970). bored). On peatlands both fire rotations But Loucks (1970) has suggested that in and maximum longevities were probably some temperate forest ecosystems periodic longer, but many spruce swamps burned in random perturbations by fire are essential the same fires that consumed the adjacent to the maintenance of long-term diversity uplands. and stability. I join this view, and will sug- White spruce, balsam fir, and northern gest here that fire was the key rejuvenating white cedar are common understory ele- factor in the Canoe Area, maintaining a ments beneath the pines, aspen, or birch. dynamic mosaic of forest-age classes and So is black spruce in many cases. In a sur- community types, keeping species diversity prising number of such cases, however, and production high, and maintaining many individuals of these four species are long-term stability of the system. Fire ex- really not much younger than the pioneer clusion is now causing widespread succes- overstory species they associate with. This sional changes that could impoverish the suggests that reproduction often begins not flora and fauna, block nutrient cycles and long after the fire even for these ‘Lclimax’J energy pathways, and lead to reduced sys- species. They usually perish in the same tem stability. fires that destroy the overstory pioneers, We cannot really be sure what vegetation and in these cases at least they are caught types might develop through prolonged suc- up in the same fire rotations. Surface fires cessional change, because in the past fire undoubtedly often eliminated understories always terminated successions before of these species beneath red and white pine steady-state conditions were reached. Proof stands without killing the overstory. Now, of this is that I did not find satisfactory many such understories are so advanced be- examples of climax vegetation in 7 yr of cause of fire exclusion that a surface fire fieldwork covering the entire 500,000 acres 360 HEINSELMAN of virgin forest-and this after 60 yr of al- shade-tolerant species. They saw paper most complete fire exclusion ! Rigorously birch as capable of maintaining its role by defined, a climax community is one that has sprouting. attained a dynamic steady-state equilib- The extensive studies of my colleagues rium with the environment and biota, and Ohmann, Ream, and Grigal utilized a large, is self-reproducing without further major randomly drawn field sample of the upland disturbances or perturbations of the sys- virgin forests of the Canoe Area, and com- tem. This status is reached only when all puterized analytical procedures to define elements of earlier successions have been plant communities and to study environ- replaced by climax species, and adjustment mental and successional relations (Ohmann to the new conditions has been demon- and Ream, 1971a, b; Grigal and Ohmann, strated by a complete cycle of self-repro- 1’973). With continued fire exclusion they duction. Stands that contain significant foresee the following successional trends: elements of first-generation postfire commu- 1. Lichen communities may acquire a par- nities hardly qualify. But the time required tial tree canopy and perhaps eventually de- for the development of such a convincing velop into a black spruce/feather moss case of climax is long-longer than the ac- community, 2. Jack pine-dominated com- tual period of development of virtually all munities (where black spruce is important) existing stands in the Canoe Area. This be- and the red pine community may even- ing so, one wonders whether the climax con- tually be succeeded by a black spruce/- cept is useful in understanding the real- feather moss community, 3. The jack pine world ecosystem here. community (where fir is important) and Nevertheless, it is instructive to consider most other communities seem headed to- what is known about succession in the re- ward dominance by fir, paper birch, white gion. Numerous phytosociological studies cedar, white spruce, and to a lesser extent, have predicted a climax vegetation, or at black spruce. The tall shrub layer may be- least the direction of successions, by ex- come dominated by mountain maple and trapolating from data on the composition fly honeysuckle, the low shrubs by dew- and structure of the existing vegetation. berry, and the ground flora by scattered The earliest was the pioneering work of mosses and such herbs as Clintoniu bo- Cooper (1913) on Isle Royale, an island in realis, Cornus canadensis, Aster macro- Lake Superior 60 miles east of the Canoe phyllus, Trientalis borealis, Aralia nudi- Area. He defined several successions con- caulis, Cop tis groenlandica, Linnaea verging toward a white spruce/balsam borealis, and Gal&m. fir/paper birch climax. Buell and Niering They recognize that these trends may be (1957) obtained data on a series of old interrupted by fire, windstorms, insect out- fir-spruce-birch communities in the Canoe breaks, diseases, and the influence of many Area and in Itasca Park, but they recog- animals. The most significant tree added to nized that all of their stands still showed the list of potential climax-dominants is evidence of a pine generation and thus were northern white cedar, which they believe not climax. (My stand-origin map shows may have the highest potential for replac- their Moose River stand to be a first-gen- ing other species in the absence of fire. eration postfire community dating from a They also point out, however, that the 1755-1759 burn.) Fir was prominent and structure and composition of the virgin for- reproducing successfully in all of their ests are more closely related to the length stands-suggesting that it would maintain of time since the last fire for each stand, a dominant role, barring fire or other dis- and probably to the character of that fire turbances. Scanty white spruce regenera- and the age and composition of the former tion suggests a secondary role for this stand than to all of the other environmental FIRE AND THE NATUR.Al. ECOSYSTEM 361 factors studied (slope, aspect, elevation, soils, etc.). These studies all rely on extrapolations from data collected largely in stands of postfire origin, but the actual number of years since fire was not a variable in most analyses. My stand-origin maps provide a record of the present age-class mosaic, and the gross areas occupied by Grigal and Ohmann’s communities are known (Table 2). Yet we still lack a plant community map that can be related to stand ages and to the successional projections of Ohmann, Ream, and Grigal. In another study, too extensive to publish in full here, Albert Swain and I did relate the stand composition and age structure of certain postfire communities to the actual time interval since the last fire. Data were taken in 32 stands: 22 jack pine-dominated communities, 6 red pine, 3 white pine, and 1 spruce-fir. In each stand we collected data on: 1. age structure by tree species and crown position in the canopy, 2. stocking by species, crown position, and diameter, and 3. composition, abundance, and cover for the shrub, herb, and ground FIG. 4. Jack pine stand of 1864 origin, killtvl layers (by a modified Braun-Blanquet sys- by crown fire in Little Sioux Fire, 1971. (Plot tern). St’ands were selected to cover the full 1, Table 7.) Nearly 40,000 jack pine seedlings ~(‘1 available range of age classes in the jack acre present. Light areas in foreground are granite bedrock exposed by burning off lichens ((.“lrl- pine series, and a few key stand ages in the do&u). About 50 yr are required for lic~hm other communities. The fire history of each regrowth. Photo taken July 1972. stand was determined by tree-ring and fire-scar analyses. Here I summarize cer- trees show that the species was formerly tain findings relevant to the present more abundant. Throughout this locality, discussion. scattered red and white pines and white Our plots in jack pine-dominated com- and black spruces of the same age class also munities show succession to either exist. The area may not have supported a fir-spruce-birch or black spruce-feather dense jack pine forest because most of the moss types, as predicted by Ohmann and individuals examined had many low limbs, Ream (1971b). However, these successions suggest’ingthat they were open-grown. The were never entirely completed (Tables 7, stocking of other species of the same age 8 and Figs. 68). A 1727 burn extending class also seems high. A clear case of suc- from Frost and Cherokee Lakes east to cessionin a formerly well-stocked jack pine Winchell Lake supports the oldest rem- forest is represented by stand 29, located nants of jack pine forest we found (see in Sec. 8, T65N, R14W on the south side of stand 30, Tables 7 and 8, and Fig. 8). Only the Echo Trail, in a 1755 burn. Succession six living jack pine were actually found in to fir-spruce-birch was also advanced in this age class, but numerous dead and down this stand, but numerous tall, well-pruned, HEIlrjSELMAX

FIG. 5. Thirty-three-year-old jack pine stand on the Cherokee Lake Eurn of 1936. (Plot 23, Town Lake, Tables 7,s). Photo taken 1969.

FIG. 6. One-hundred-year-old jack pine stand on an 1864 burn. Little Shell Lake. A few small northern white cedars fringe the lakeshore. Succession not advanced here. Photo taken 1967.

215yr-old jack pines still remained (Ta- 1903, 1894, 1875, and 18634 burns. If bles 7, 8). these stands follow the successional trends It is clear from our stand data that jack shown, some jack pine forest would persist pine can persist as a scattered overstory at least another 200 yr with continued fire element in the Canoe Country for at least exclusion. However, large-scale successions 210-250 yr without fire. Most present virgin to fir-spruce-birch and black spruce/feather jack pine stands date from 1936, 1910, moss communities would begin to reach FIRE AKD THE NATURAL ECOSYSTEM 3 63

FIG. 7. Remnant of old jack pine forest on FIG. 8. h 243-yr-old jack pine on Gordon Lake, a 1755 burn near Echo Trail, 20 miles northwest within a 1727 burn. Succession to fir-spruce--1,irch of EIy, Minnesota. (Near Plot 29, Tables 7, 8). is far advanced in this, the oldest former jack The jack pine in foreground was 215 yr old. Note pine stand studied. (Plot 30, Tables 7, S.) Photo advanced succession to balsam fir, white spruce, taken 1969. This tree, and five others in the same :md paper birch. Photo taken 1970. This area age class, are the oldest known jack pines in burned in a crown fire during the Little Sioux the Great Lakes region. Fire, 1971.

completion in 90-100 yr (2070 A.D.), as closer to 200 yr. Succession to fir-sprucc- the jack pine now present on many 1863- birch and cedar should thus proceed on a 1864 burns reached the limit of its longev- slightly faster timescale than for jack pine ity. The final demise of jack pine, now the (Fig. 9). most conspicuous forest dominant, would No red pine stands studied in detail had come about 2170 A.D. if no more fires escaped fire longer than 202 yr at the time occurred. of our research. The main red pine over- We could not obtain comparable data for story in our Boulder Bay stand (A-8, lo- the important aspen-birch types because of cated in Sec. 32, T67N, R13W, Lac T,aCroix problems in getting countable increment Natural Area) dated from a 1681 burn, cores from old aspens.However, these com- but the st.and had been partially burned munities are often intermingled with jack through in 1755 and 1767 (Table 9). The pine types of the same age class, and their oldest red pine bored here was 283 yr old. age structures are similar, although quak- Scattered white pines and white and black ing aspen may have a maximum longevity spruce 30-150 yr old were present in the 364 HEINSELMAN

TABLE 7

STOCKING OF JACK PINE-DOMINATED VIRGIN FORESTS BY SPECIIGS AND TIME SINCE STAND ESTABLISHMENT AFTER FIRE, BOUNDARY WATERS CANOE ARE.~. (DATA INCLUDE ALL TREES 1 IN. OR LARGER, D.B.H.)~

Date No. Numbers of trees per acre Trees/at Little Sioux 1 1971 1 39,910 250 20,720 60,880 Little Sioux 2 1971 1 12,460 2170 6770 21,400 Town L. 23 1936 33 3400 100 700 4200 Cherokee L. 31 1936 34 1920 360 1260 340 3880 L. of Clouds 12 1910 59 450 330 290 50 280 10 1,410 L. of Clouds 13 1910 59 530 1690 440 130 140 2930 Cummings L. 20 1910 59 740 110 850 Saganaga L. 16 1903 66 190 5 320 20 3.5 105 675 Turtle L. 17 1903 66 380 170 250 10 310 1120 Ester L. 14 1894 75 290 180 260 80 810 Cummings L. 19 1894 75 380 195 5 320 10 910 Moose R., S. 2 1894 75 290 260 30 580 Ada Cr. 33 1875 95 70 240 95 25 430 Moose R., S. 3 1864 105 105 160 15 45 145 470 Ester L. 15 1864 105 210 10 370 90 30 710 Insula L. 25 1864 105 140 50 200 20 410 Keeley Cr. 27 1854 116 80 45 45 20 135 30 355 Cash L. 32 1846 124 60 230 85 15 265 5 5 665 Amoeber L. I1 1827 142 200 210 30 110 140 10 700 N. Hegman L. 28 1822 148 80 585 55 720 Seagull L. 6 1801 168 30 10 300 185 5 485 5 20 1040 Seagull L. 7 1801 168 40 585 15.5 25 45 10 5 865 Echo Trail 29 1755 215 20 80 65 20 470 655 Gordon L. 30 1727 243 5 25 245 10 800 25 1110 a Basis: One measured circular plot in each stand (plot sizes range from 35 to >60 acre, depending on stand density and age). “Other species” includes quaking and large-tooth aspen, white pine, red maple, and mountain ash. Data from Little Sioux Burn are for 1-yr-old seedlings based on 100 mil-acre quadrats per stand. understory. Succession to fir-spruce-birch cause the virtual elimination of red pine was not advanced, and all the fir and birch from the Canoe Country by about 2350 understory trees aged were 60 yr or less old. A.D. The species might persist on cliffs, The oldest individual red pines cored are steep rocky slopes, and barren islands, but now 378 yr old (the Three Mile Island the stately groves of large old red pines now stand on Seagull Lake). Succession to so characteristic of many areas would be fir-spruce-birch and cedar certainly is oc- gone. curring in most old red pine stands, and I The oldest white pine-dominated com- estimate that without fire the last red pine munity studied was found east of Larsen overstory elements would disappear 400- Lake on a narrow stretch of land between 450 yr after stand establishment (Fig. Gaskin and Winchell Lakes, just northeast 10). The youngest virgin stands are now of a series of ponds and wetlands. This 30-60 yr old. Thus total fire exclusion could physiographic location had evidently pro- FIRE AND THE NATURAL ECOSYSTEM

TABLE 8

BASAL AREA OF JACK PINE-DOMINATED VIRGIN FORESTS BY Spwxes AND TIMF: SINCE STAND ESTABLISHMENT AFTER FIRE, BOUNDARY W.~TERS CANOE ARE!\. (DATA INCLUDE ALL TREES 1 INCH OR LARGER, D.B.H.)~ --_ _-- .

___ Date No. Basal area-sq ft per acre sq ft ,‘w Town L. 23 1936 33 118 1 7 126 Cherokee L. 31 1936 34 142 4 21 3 172 L. of Clouds 12 1910 59 78 22 11 4 12 1 127 L. of Clouds 13 1910 59 67 80 10 10 10 Ii7 Cummings L. 20 1910 59 104 1 103 Saganaga L. 1903 66 1 36 1 3 21 lS7 16 75 P Turtle L. 17 1903 66 97 21 31 1 8 1.1X Ester L. 14 1894 75 102 1.5 7 2 126 Cummings L. 19 1894 75 123 38 1 4 1 166 Moose R., S. 2 1894 75 81 43 2 128 Ada Cr. 33 1875 95 56 64 IY 4 1x7 Moose R., S. 3 1864 105 72 2.5 1 :i 6 107 Ester L. 15 1864 10.3 68 5 5.5 1 2 131 Insula L. 25 1864 105 99 10 4:; 1 I .i:!J Keeley Cr. 27 1854 116 51 4 8 6 2‘)I ‘2 !13 Cash L. 32 1846 124 41 43 10 2 21 I 124 Amoeber L. 11 1827 142 96 3’2 12 7 7 1 1.i A N. Hegman L. 28 1822 148 56 42 2 100 Seagull L. 6 1801 168 24 19 17 .j 1 29 4 1 100 Seagull L. 7 1801 168 32 31 15 4 3 1 1 ?(7 Echo Trail 29 1735 215 30 I1 “4 7 30 102 Gordon L. 30 1727 243 6 6 37 17 82 1 149

a Basis: One measured circular plot in each stand (plot size ranges from 3s to >fo acre, depending on stand density and age). “Other species” includes quaking and large-tooth aspen, white pine, red maple, and mountain ash. tected the area from fire for some 360 yr- doubtedly of postfire origin. Charcoal was longer than any other site investigated. Our found at the base of the humus layer at plot (A-5) was taken 200 ft from the west all four sites checked. No trees had de- shore of Gaskin Lake, about l/s mile north- tectable fire scars. The time of the last sig- west of the portage to Winchell Lake (Sec. nificant fire was between about 1610 and 26, T64N, RlW) (Table 10, Fig. 11). A 1595 A.D., but a light surface fire might sparse supercanopy of very large white have occurred about 1670, because all of pines gives the stand the appearance of still the old pines had center rot beyond that being a pine forest, but the vegetation time, and none of the trees other than the otherwise is more advanced successionally pines apparently originated before 1670. than any other stand we visited. The lar- The main canopy consists of white cedars gest white pine measured was 41 in. in di- up to 296 yr old and 22 in. in diameter, ameter and more than 100 ft tall. The five white spruce up to 185 yr old and 25 in. pines bxed for ages all had rotten centers, in diameter, and paper birch up to 162 yr but all yielded estimates between 323 and old and 16 in. in diameter. The understory 368 yr. The stand is thus even-aged and un- is chiefly fir, up to 13 in. in diameter and 366 HEINSELMAN

FIG. 9. This lO&yr-old quaking aspen stand was totally killed by a crown fire that consumed a budworm-damaged fir-spruce understory during the Little Sioux Fire of May, 1971. The killed stand originated after an 1864 burn. Photo taken October 1971. At this time there were 77,000 new aspen suckers and 2360 aspen seedlings per acre.

121 yr old. Some cedar saplings as small budworm damage to the fir understory is as 2 in. in diameter are also present, some only moderate. A moderate tall shrub layer of layer origin. New seedlings of fir and consists largely of Acer spicatum and cedar are abundant, and a few white spruce Corylus corn&a. The most abundant herbs seedlings were found. Some seedlings of are Cornus canadensis, Ara1i.s nudicaulis, paper birch occur on rotten logs. Spruce Linneae borealis, Mitella nuda, Galium

TABLE 9

ST.%ND STRUCTURE BY SPECIES AND AGE RANGES FOR A 28%YR-OLD RED PINE STAND ORIGINAT- ING AFTER A FIRE IN 1681. GROUND FIRES BURNED THROUGH STAND IN 1755 AND 1767- NO EVIDENCE OF FIRE SINCE (STAND A-8, BOULDER BAY, LAC LA CROIX, BOUNDARY WATERS CANOE AREA. DATA TAKEN 1969, INCLUDES ALL TREES OVER 1 IN. D.B.H.)

cd E m .2 2 22 Sample tree ages by crown position class Q 3 a? 2 Domi- Codomi- Species a2 8 ii% nant nant Intermediate Suppressed Inches No. sq ft Years Years Years Years Red pine 2-22 155 180 283 278 280 106-266 White pine 1-14 285 20 - - 153 32-142 Black spruce l-6 90 6 - - 103 56-96 White spruce l-10 10 3 - - 156 - Balsam fir l-4 90 3 - - - 30-44 Paper birch l-4 175 3 - - - 21-60 Total l-22 805 215 283 278 103-280 21-266 FIRE AND THE NATURAL ECOSYSTEM

FIG. 10. Interior of a 280-yr-old red pine stand on Kamshcad Lake. Note stand deterioration from Find breakage, and advanced succession to fir-spruce-birch. This stand originakd after a fire in 1681. Photo taken 1966. Portions of this forest burned in crown fires and surface fires in the Little Sioux Fire, 1971. (Stand A-8, Tahlr 9, (not shown) la&cd :j dense understory, and had not yet been wind-damgcd.) triflorum, Maiunthemum canadense, Trien- on the ground and on rotten logs; the nlore talis borealis, and Aster macrophyks. C,O~III~NN~species are: Pleuroxium schreberi, Lycopodium annotium and L. clavatum are Hylocomium splenders, Hypnum crista- also cornfnon. Mosses are abundant, both cnstrensis, Dicranum ruyosum, Polytri-

TABLE 10

ST.\ND STRUCTURE BY SPECIES AND AOE R!.NGES FOR .% 360-YR-OLD WHITE PINE STAND SHOWISC ADVANCED SUCCESSION TO FIR-SPRUCE-CEDAR-BIRCH. (STAND A-5, G~SKIX LIKE, BOUNDAI~Y WATERS CANOE AREA. THIS STAND ESCAPED FIRE LONGER TH.%N ANY OTHER STLDIM- LAST SIGNIFICANT FIRE 1595 TO 1610 ‘1.~. I).w.i T.UXN 1969, INCLVDES .~LL TNKIM OVER 1 IX. m3.H.) ~-.~-_I__~__ E 5 2 3 ‘SE Sample tree ages by crown posit,ion class 4 2 -_- -.---~ -.~~ . r& Q ai; ._a d 2 25 Inter- sup- s6 pecies a2 b F9a Dominant Codominant mediate pressed Inches No. sq ft Years Years Years Yenrs White pine 33-41 5 33 3X-368 White spruce 18-25 10 36 178-18.5 - White cedar 1-22 30 “8 -.- 250-296 37-96 Balsam fir 1-13 673 69 _- 99 9.5-12 1 38M3.5 Paper birch lo-16 20 23d 160-162 96 _--- Total 1-41 740 178 178-3368 99-296 9.5-121 37-96 368

FIG. 11. Remnant super-canopy of 360-yr-o:d white pine, with advanced succession to fir-spruce-cedar-birch in main canopy and understory. Stand A-5, Gaskin Lake, Table 10. This area, which may have escaped fire since about 1610 A.D., supports the most successionally advanced stand studied. Photo taken 1969. chum commune, Mnium punctatum, and part of a well-stocked white pine forest. Mnium afine. The litter-plus-humus layer Many individuals had died or been wind- ranges from 1 to 4 in. in depth, 2 or 3 in. broken within the past 50-100 yr-the being typical. This stand was clearly once ground was criss-crossed with their old rot- ting, moss-covered trunks. Probably few if TABLE 11 any of the old pines will survive more than another 100 yr, and there are no understory STAND STRUCTURE BY SPECIES AND AGE R.~NGES FOR .4~ EARLY POSTFIRE SPRUCE-FIR-CEDAR- pines to replace them. Thus, at about 460 BIRCH STAND, BOUNDARY WATERS CANOE yr after fire, succession to fir-cedar-white ARES (STAND A-24, LONG ISLAND RIV>;R, spruce and birch will be complete. The fir WITHIN THF: FROST LAKE BURN OF 1936. understory now present is probably at least DATA TAKEN 1969, INCLUDES ALL TREES OVIZR 1 IN. D.B.H. ALL the second or third generation of that spe- SPECIES REPRODUCED SOON cies to grow beneath these old pines. AFTER FIRF,) Many spruce-fir-birch and cedar stands Basal are really of direct postfire origin. An ex- Diam- Trees area ample was studied on the east side of the eter per per Sample Long Island River, in a 1936 burn (Plot range acre acre tree ages A-24, Sec. 24, T64N, R4W, Table 11). The Species (in.) (no.1 (sq ft) (yr) fire occurred 33 yr before our plot study, White spruce 1-5 1450 55 26-31 but the age range among all trees sampIed Black spruce 1-4 450 24 27-32 was only 19-32 yr. Most trees of all species, Balsam fir l-4 450 14 24-30 White cedar l-2 550 4 25-31 including the “climax” specieswhite spruce, Paper birch 1 300 2 19-22 northern white cedar, and fir, had origi- White pine 2-3 100 3 26-27 nated within 5 yr after the fire. The seed Jack nine 5 50 7 26 source was apparently an unburned 1727- Total l-5 3350 109 19-32 origin mixed-conifer forest across the river. FIRE AND THE NATURAL ECOSYSTEM 369

If such a stand were sampled 150-200 yr status of succession, let us return to the in- after its origin, it might easily be mistaken terrelationships between succession, species for a climax forest simply because a second diversity, community stability, and produc- generation of fir, cedar, and spruce was de- tivity. The data that Swain and I assem- veloping as an understory beneath the first bled, and those of Ohmann and Ream generation of postfire trees. A similar situa- (1971b) suggest that the species diversity tion exists with black spruce/feather moss of many individual stands increases with communities, which apparently could de- succession following fire for at least lOO- velop through succession, but most actually 250 yr. Certainly this is so for the tree have first generation postfire overstories, stratum, where maximum diversity comes in both on uplands and peatlands (LeBarron, the midsuccession years when both pioneer 1939 ; Heinselman, 1957,1963). and shade-tolerant invaders are present. A possible problem with past studies of But if succession proceeds for 300-500 yr, succession emphasized by our age-structure most areas would then show a decline in work is that much of what appears visually diversity as the pioneers disappear. to be succession is really just suppression. If the unit of concern is a large region The “sapling” understories of many stands like the Canoe Area, however, and not just were nearly as old as the overstory ! This individual stands, then diversity for tht is particularly t’rue of black spruce beneath whole ecosystem is a function of both tht jack pine. Black spruce often seeds-in well composition of individual communities and following fire, but regeneration may come their relative abundance and arrangeIn& in for several years. Spruce seedlings also on the landscape. Maximum divcrsit$y here grow more slowly than the pines in their is attained with a full spectrum of succes- first few years. Once in a subcanopy posi- sional stages and community types pattern- tion, such trees may survive more than a ing the landscape, arranged like patches on century in a suppressed condition. For ex- a quilt. There would be new burns, early ample, in an 1864 burn on Lake Insula we postfire successions, maturing pioneer for- found the dominant jack pines to be ests, midlife stands showing invasion of 102-105 yr old and up to 15 in. in diameter, shade-tolerant species: and very old com- while a suppressed black spruce in the same munities. The scene, over time, would IX: stand was only 5 in. in diameter but 97 yr like a slowly changing kaleidoscope. This old. On a 1936 burn on Cherokee Lake the is clearly the may it was in the primeval dominant jack pines were 4-6 in. in diame- ecosystem. Diversity for t’he system as a ter and 33-34 yr old, while all the black whole could only be described if hundreds spruce were already suppressed and only of square miles were studied and mapped 1-3 in. in diameter, but their ages ranged simultaneously-as on Earth Resources from 28 to 32 yr. These are not isolated Satellite imagery. eases-we found the same situation on vir- If, through fire exclusion, system-wide tually all plots in jack pine/black spruce successions eliminate this patterning, then stands. The same situation exists to a lesser the diversity of the total system would hc degree with white spruce and northern reduced. Within 200-3UO yr fir-spr\:cc- white cedar. The only two understory spe- cedar-birch and black spruce/feather moss cies that are commonly much younger than forests might occupy essentially all upland the overstory are balsam fir and paper sites, and the pines and aspens might disap- birch. These poor correlations between di- pear. So might, much of the shrub, herb, and ameter and age should make one cautious ground vegetation now characteristic of in generalizing about succession based on pioneer forests. Indeed, over most of the size-class analyses alone. area the really early postfire successions With this background on the present are already missing because there have 370 HEINSELMAN been no large burns since 1936, save the dead wood or soil organic layers, it creates Little Sioux Fire of 1971. But these changes a highly fire-susceptible forest that usually are not yet permanent, because the root does not directly regenerate itself following systems and seed sources of the pioneer spe- fire. cies are still present and capable of resur- A second reason to doubt the stability gence if fires recur. Permanent fire exclu- of extensive fir-spruce-cedar-birch forests sion is another matter, however. For if fire is the susceptibility of mature fir and could be kept out of the system indefinitely, spruce to wind breakage and uprooting. If such characteristic species as jack pine, large areas were covered with mature aspen, red pine, white pine, blueberry, pin- stands, extensive blowdowns, generating cherry, and many more might be virtually fuel concentrations that would add to fire lost from the system. intensity can be foreseen. Whether “climax” vegetation, presum- Without fire, black spruce-dwarf mistle- ably fir-spruce-cedar-birch forest, would be toe could ravage many black spruce-feather more stable than the heterogeneous vegeta- moss forests-another type that might in- tion mosaic produced by periodic fires crease on both uplands and peatlands with should also be considered. There are several continued succession (Anderson and Kau- reasons to think it would not. First, exten- fert, 1959). Fire was apparently the natural sive mature fir/white spruce stands are check on this parasitic plant, and mistle- highly susceptible to the spruce budworm toe-killed or injured stands are very flam- (Batzer, 1969; Van Raalte, 1972). Succes- mable (Irving and French, 1971). The sta- sion to fir-spruce on the scale expected with bility of this type too is therefore suspect. fire exclusion would produce ideal condi- Unlike fir-spruce-birch, however, fire aids tions for repeated outbreaks by this native the direct regeneration of black spruce insect, which is capable of killing most of communities. the balsam fir over large regions. Just such The mean annual production of the “cli- an outbreak has been in progress in the max” forests would probably also fall short Canoe Area since about 1956, perhaps sus- of that in the natural fire-dependent system tained by the unnaturally extensive succes- because of partial blocking of nutrient cy- sions to fir throughout northeastern North cles and energy flow. In nature, fire was the America caused by fire protection. Such agent that periodically reduced the litter outbreaks do not eliminate fir, however. and humus accumulations of upland sites, Enough new seedlings are always present and peat accumulations on wetlands. It not to regenerate the species. Mature white only reduced these layers physically, thus spruce often survives. But the mature and influencing soil temperature, soil moisture, sapling fir component of most stands is and other factors, but it also recycled the killed over large areas, and vast concentra- mineral elements and carbon they con- tions of dead wood are generated, both tained. Both kinds of recycling are impor- standing and down. Tree lichens (Usnea tant in maintaining the long-term produc- spp. and Alectoria spp.) make these areas tivity of northern forests, although good extremely flammable. The probability of data on these questions are only now being lightning or man-caused ignition of such accumulated. The detritus food chain be- areas therefore becomes a factor in the sta- comes the major energy pathway in the ab- bility of such an ecosystem. One might sence of fire, but it is doubtful that it is argue that the budworm could become the as effective in recycling nutrients in north- agent for recycling the ecosystem instead ern conifer forests. of fire, but this cycling is certainly incom- For the case of fire exclusion it is haz- plete (Grigal and Ohmann, 1973.) And ardous to project either changes in stand since the budworm does not consume either composition or environmental interactions FIRE AND THE NATURAL ECOSYSTEM 371 very far into the future, because fire exclu- it avoids the real challenge of understand- sion would cause changes in ecosystem pro- ing nature on her own terms. cesses that have not occurred for at least 9300 yr. The entire system evolved in an WILDLIFE HABITAT AND FIRE environment that did include periodic fire. An understanding of the role of fire in There are so many interactions conditioned the Canoe Area’s ecosystem requires at by this history that the effect of eliminating least a brief look at the interactions be- fire can hardly be predicted with our tween vegetative successions and wildlife present knowledge of the system. Even the habitat. Most native mammals and birds possibility of excluding fire must be ques- have habitat requirements that correspond tioned. Lightning ignitions at times when with niches in various postfire successional control cannot be quickly achieved seem stages. Inasmuch as all the natives found guaranteed by long-term fuel accumula- niches in a fire-created vegetative mosaic tions or periodic fuel peaks. The climatic in primeval Gmes, this is not surprising. history of the region makes it clear that Some examples are : severe drouths will recur. When they do, Moose. Large quantities of nutritious the probability of large fires seems high. It browse are required in winter, but this ani- is interesting, too, that the maximum mal, if well fed, is large enough to cope longevity of most pioneer trees is far longer with snow at least 20 in. deep. Aspen, birch, than the natural fire rotations for the vege- willow, red maple, and pincherry, all com- tation types they dominate. The possibility mon post’fire sprouters, are heavily used of excluding fire long enough to eliminate (Krefting, 1951; Peek, 1972). Large burns these species seems remote. arc therefore suitable feeding areas, unless In much ecological literature as well as the snow is too deep. Two or three years the popular press, fire has been viewed as after fire the regrowth protrudes above the: unnatural, man-caused, and a “distur- deepest snows, and moose can then forage bance” somehow not part of the ecosystem. most of the winter. Yearlings may be ali But for the Canoe Area at least, it must important factor in populating new burns now be seen as just a perturbation within (Peek, 1972). Moose also benefit from the the system. It was an essential factor in overhead cover of conifer forests on cold maintaining the kind of long-term stability winter nights and can browse the foliage and diversity recorded in the pollen and of sapling fir. Thus a combination of recent charcoal diagrams of Craig (1972) and burns and adjacent maturing forest (near Swain (1972, and this symposium). The waterways for summer range) should make composition, structure, and dynamics of the a productive habitat complex. Moose are virgin forests can best be understood if we now abundant in certain recently logged or concentrate on understanding how the sys- burned sect,ions of the Canoe Area? but less tem functions with fire as part of that sys- common in large areas of mature forest. tem. Rigorous studies of the interrelation- Beaver. Stands of deciduous trees within ships between fire periodicity, succession, a few hundred feet of lakes and streams are and the species diversity, stability, and required. Aspen, paper birch, and willow product,ivity of this fire-dependent eeosys- are favored. Cuttings from these trees are tern are now possible and should be pur- used for dams, lodges, and winter food sued. Much of the needed data are avail- caches. In the primeval system these trees able and this opportunity to construct an were found on burns, but within 70-100 yr ecosystem model of a real-world, fire-de- after a fire beaver often fell all of the aspen pendent system should not be missed. The and birch within reach of waterways. They search for stable communities that might must then move on to a newer burn. Fire develoD in the absence of fire is futile. and exclusion is now preventing the regrowth 372 HEINSELMAN of aspen-birch stands, and a high per- there clearly has been less fire since 1910 centage of the available stands have been than in the preceding 250 yr when caribou cut by beaver. A population decline can be were present. For example, caribou were expected. abundant for at least 30 yr after the fires Snowshoe hare. In natural ecosystems of 1864, which burned some 44% of the vir- hares attain peak populations in young gin forest. And several hundred thousand postfire stands, especially of aspen and acres of contiguous virgin forest with a sim- birch, because of their need for thin-barked ilar fire history remain in Quetico Provin- woody stems for winter food. Five to thirty cial Park just to the north. But when the years after fire are probably the best years caribou disappeared, much of the virgin (Grange, 1965). In recent decades hares forest of both the Canoe Area and Quetico have not been abundant except on recently consisted of stands 10-60 yr old, dating from burned or cutover areas. the burns of 1864, 1875, 1894, and 1910; White-tailed deer. This deer was uncom- and logging had just eliminated most of the mon in northeastern Minnesota in primeval old white and red pine forests from adja- times, but a large population increase came cent land. In the Canoe Area today tree with the logging and burning of the mature lichens are found largely on the lower limbs white and red pine forests. Peak popula- of old fir and spruce, and on dead fir killed tions came between 1930 and 1950. With de- by the budworm. Ground lichens are most creased timber cutting, plus fire exclusion, abundant on open bedrock ridges, which deer have since declined sharply. Many become well covered by lichens 60-100 yr favored browse plants occur on recent burns, after fire. Some browse plants used by cari- but deer perhaps cannot use large burns bou are found in old forests as well as on effectively because of deep snow and preda- burns (Acer spicatum, Pyrus americana, tion (Peek, 1972). Vogl and Beck (1970) Cornus stolonifera, Xalix spp., and Vi- have documented the prompt response of burnum rafinesquianum) . Sedges and some deer to fire in northwestern Wisconsin. wintergreen herbs are also used. I believe Woodland caribou. Caribou were com- the main habitat change working against mon in the Canoe Country until 1900 but caribou was a regional decrease in the pro- disappeared about 1925, and from Minne- portion of old stands supporting tree lichens sota entirely by 1942 (Gunderson and Beer, and perhaps in the proportion of open 1953; Cringan, 1957). In winter these ani- ridges supporting a good growth of Cla- mals must have subsisted on a combined donia. But several areas with these charac- diet of tree lichens (Usnea and Alectoria), teristics did exist at the time caribou disap- ground lichens (Cladoniu rangiferina, C. al- peared, and habitat changes could have pest&s, etc.), and browse. The relative im- been responsible for their extirpation only portance of browse and lichens is still not if very extensive areas with a significant clear, but existing caribou populations in proportion of lichen-bearing stands are es- Ontario, within 200 miles of the Canoe sential. The persistence of a small herd on Area, use both (Cringan, 1957; Ahti and the Slate Islands in Lake Superior (Crin- Hepburn, 1967). There is speculation that gan, 1957) suggests that such vast areas are caribou disappeared from Minnesota be- not essential to survival, although they cause logging and fires between 1870 and may be necessary to support a significant 1930 eliminated the old forests and their regional population. Probably both exces- associated lichen crops. This is tenable for sive hunting and regional habitat changes northern Minnesota as a whole, but for the were involved in the elimination of caribou. remaining virgin forests of the Quetico-Su- In any case, the forests of much of the re- perior country it is too simplistic an ex- gion are now 60-150 yr old, ground and tree planation, because there was no logging, and lichens are abundant, and there is reason FIRE AND THE NATURAL ECOSYSTEM 37.3 to believe the area could again sustain cari- burned areas (Books, 1972). Apparently bou. Restocking probably is necessary. they survived the fire underground and rc- Eastern timber wolf. This endangered appeared as soon as it had passed. After subspecies is the largest carnivore in the both the first and second growing seasons Canoe Country’s ecosystem. Its principal traplines yielded nearly a full complement prey are the deer, moose, beaver, and of small mammals: redback vole, woodland formerly caribou. This strongly social and deermouse, meadow vole, masked shrew, highly territorial animal has pack terri- least chipmunk, and meadow jumping tories that may encompass 50-125 sq miles. mouse. The red squirrel is temporarily dis- Packs are family groups and typically con- placed by fire, but its niche is in maturing tain 3-15 individuals (Mech, 1970; Mech jack pine, black spruce, and red and whit? and Frenzel, 1971). Enough area of early pine stands-all postfire communities. postfire or postlogging plant communities Rzlffecl grouse. In northern Minnesota must exist within a pack’s territory to sus- this grouse depends heavily on the buds of tain a surplus of the prey species that de- aspen for winter food, especially on thcb pend on such communities (deer, moose, staminate flower buds of quaking aspen beaver). Formerly caribou may have been (Svoboda and Gullion, 1972). A patchwork common in mature forests too, giving the of aspen stands of different ages, inter- wolf available prey in both old and young spersed with conifers, provides good feeding forests. But today, old stands contain few habitat plus winter shelter. This was t,hc prey animals, and the wolf is not common character of the primeval forest. Succession there. Pack sizes may be decreasing (Mech, due to fire exclusion is now gradually re- in press). Further declines in populations ducing ruffed grouse habitat, although there can be expected if fire exclusion continues! is still much good habitat in the younger especially if caribou are not reestablished. aspen forests. Black bea?. The bear is omnivorous and Other birdlife. The primeval mosaic of thus can find food in many habitats. But forest age classes and successional stages the important berry-producing plants, such created by fire provided niches for all as blueberries, raspberry (Rubus idaeus) , native land birds. For example, several SJW- juneberries (AnLeZnnchie,r spp.), and cher- ties of woodpeckers occur sparingly in ma- ries (Pntnus spp.), are most abundant 2 to ture forests, but concentrations of these perhaps 20 yr after fire or logging. Thus birds developed on the Little Sioux Burn recent burns or cutover areas are important in the first and second years after fire. They haljitats for bear. In primeval times this were seeking the abundant larvae of wood- animal undoubtedly frequented burns dur- boring beetles and harkbettles in fire-killed ing berry season, but today there are few or fire-injured trees. Notably abundant, burns, and must berries are found on cut- were the otherwise uncommon northern over areas beyond the virgin forests. Rasp- three-toed woodpecker (Pi&odes tridtrc- berries are an exception, because they also tylus) and the black-backed three-toed abound in openings in budworm-killed fir woodpecker (Piciodes arcticus). In contrast, stands. many warblers seem especially abundant in Small mammals. Most species native to mature forests with a fir element during the Canoe Country seem well adapted to outbreaks of the spruce budworm, upon survival during and after fires. Traplines which they feed (MacArthur, 1958). This run on the Little Sioux Burn 3 wk after the insect was periodically epidemic in old fire by Milton Stenlund, Minnesota De- stands in primeval times as well as now partment of Natural Resources, showed (Blais, 19653. that redback voles, chipmunks, and deer Clearly the entire biota was adapted to mice were active even in the most severely an environment that included periodic fire. 374 HEfNSELMAN

Wholesale succession of the forest due to If the public holds such values for the fire exclusion is now restructuring the entire virgin landscapes of the Canoe Area, and system, and gradually eliminating the if management is to respond to these val- niches of many formerly abundant wildlife ues, then the presettlement ecosystem species. While some might find their niches should be maintained or where necessary expanded in such an ecosystem, for exam- restored to the maximum extent feasible. ple, warblers or caribou, the removal of fire A wide-range of vegetation and fire-policy would apparently cause a significant loss alternatives can be tested against such val- of diversity and an overall decrease in ues and objectives. Four options often con- wildlife. sidered are : 1. Exclude all fires as far as possible and RESTORING FIRE TO accept the vegetative and wildlife popula- THE ECOSYSTEM tion changes that ensue (gradual succession to fir-spruce-cedar-birch and black Wilderness preservation programs for the spruce/feathermoss communities with their Canoe Area and similar regions with fire- associated wildlife). Also exclude all me- dependent ecosystems hinge on the public chanical vegetation manipulation. (This values and objectives to be served. Many has been the practice in the “No-cutting values attributed to wilderness depend Zones” of the Canoe Area.) on maintenance of the natural system 2. Allow all natural forces a free rein, in- (Brower, 1960; Falls, 1967; Heinselman, cluding lightning-caused fires. (One might 1965a, b, 1970a; Leopold, 1921; Littlejohn still control man-caused fires here.) Ex- and Pimlott, 1971). Those most closely clude mechanical manipulation. linked to natural ecosystems include: 3. Create vegetative disturbances similar 1. The cultural, aesthetic, and psycho- to those produced by tire with noncommer- logical value of experiencing the natural cial tree cutting, where necessary followed world. by prescribed fire or mechanical soil treat- 2. The value of rare, endangered, or ment. Follow treatments with seeding or unique species, plant communities, environ- planting and other cultural measures as ments, and ecosystems in maintaining the needed to simulate the natural vegetation. diversity of the Earth. 4. Reestablish the natural fire regime 3. The scientific value of understanding with prescribed-controlled burning of intact natural systems-especially large-scale eco- virgin forest communities. Set fires in system processes that require complete standing forests to duplicate the ecological systems, well buffered from outside in- effects of natural wildfires. (Carefully iden- fluences. tified and monitored lightning fires might 4. The value of natural ecosystems as also be allowed to burn when considered check areas for studies of technologically safe.) Exclude all mechanical manipula- modified systems outside wilderness. tion, seeding, and planting. 5. The value of wilderness as a reservoir Obviously there are many possible com- of plant and animal genetic stocks adapted binations and variants of these alterna- to the natural environment and uninflu- tives, and I cannot explore them all here. enced by the intentional selection or trans- I have already dealt with the ecological fer of stocks by man. consequences of Fire Exclusion (option 1). 6. The educational value of wilderness as It is still policy in most Wilderness Areas, an outdoor laboratory for study and re- and, to the extent it succeeds, it is the man- search in higher education and as a means agement practice as well. And it has advo- to increase the general public’s understand- cates. At the very least it is a defensible ing of natural environments and the ecologi- “holding action” until better alternatives cal problems facing mankind. are ready for application. Some argue that FIRE AND THE NATURAL ECOSYSTEM 37:

it is the preferred alternative, knowing full because natural fires in northern conifer well that it is really an ecological experi- forests are different from prescribed fires ment on a grand scale. However, it does in the ecosystems in which most burning carry two major risks if pursued indefi- experience has been gained so far (the nitely: 1. Fuels might eventuaIly accumu- southern pines, ponderosa pine, the se- late to very high levels, and catastrophic quoias, logging slash in the north, grass- wildfires might become inevitable in spite lands, etc.). Fires in living northern conifer of protective measures. 2. Habitat for forests arc frequently combinations of in- many abundant and interesting wildlife tense ground fires and running crown fires. species will eventually deteriorate to the Often heavy litter and thick organic-mat,ter point that populations would decline to accumulations are part of the fuel load. In very low levels. some plant communities fires burned only The second option, allowing most light- at long intervals, perhaps 50-400 yr. Their ning fires to run, carries safety risks for the ecological function was to eliminate the old Canoe Area, but it is a viable option for forest and begin successions anew. We have some mountain wilderness (Kilgore and had little experience with the deliberate use Briggs, 1972). The problem in the Canoe of such fires! but this would be essential if Area is that some lightning fires will in- wilderness ecosystems such as those of the evitably occur during severe droughts on Canoe Area are t,o be restored and main- days with high winds. Once such fires be- tained. For example, the problems are come large, control is difficult, and wind different from those of restoring fire to the shifts could threaten lives or property out- giant sequoias of California (Kilgorc, side the wilderness. In this nonmountainous 1972), because of the ecological require- terrain such fires could run many miles ment for frequent’ crown fires in the Canoe and jump large water barriers by spotting. Area. Fires such as these may have accounted for To restore fire to its natural role in the a significant percentage of the burn area virgin forests of the Canoe Area a pre- in primeval t.imes. scribed-fire program might be applied as The third option, substitution of me- follows: chanical manipulation for natural fire, is 1. The objective would be to duplicate technically feasible (at high costs), but it the frequency and severity of natural fires sacrifices most of the values of wilderness by settling carefully prescribed fires in times associated with natural ecosystems. The and places when safety and control can be problem is that once trees are cut, the seed assured. To the extent that the natural fire sources for many species are changed, and regime is achieved, the resulting forest re- the choice of the new plant community production and age structure, plant-com- rests largely in the manager’s hands. The munity composition, and wildlife-habitat. technical skills and tools of forestry then conditions would be accepted as natural. become necessary, even if the operation is Direct control of vegetative successions and noncommercial. The result is a forest man- a planned outcome would not be intended. aged by silviculture. The results of given burns, whatever they The fourth option, combining pre- might be, would be neither “good” nor scribed-controlled fire with carefully se- ‘(bad,” but simply natural. The emphasis lected and monitored lightning fires, is the would be on restoring the natural environ- only alternative for the Canoe Area that Inent. There would be no intention of cre- responds to the objective of restoring the ating specific forest communities or wildlife natural ecosystem with safety (Heinsel- populations. man, 1971). The application of this al- 2. There would be no seeding or planting ternative to large-scale northern conifer of trees, shrubs, or herbs, nor should there forest ecosystems is new to applied ecology be any need, because fire without cutting 376 HEINSELMAN

is a natural factor. It is expected that a and bulldozed firelines would be allowed. wide-range of vegetative effects would be Helicopters and conventional aircraft could achieved. Some forest stands would be be used for water bombing, equipment and totally killed. Others might receive only crew transport, observation, communica- understory removal or light surface fire or tions, and related logistical work. Electric be skipped entirely by the vagaries of fire or aerial ignition could be used for large behavior. This too would be considered units if weather, safety, and ecological con- natural and not a “failure.” siderations required. (The policy on equip- 3. The area burned per decade, and the ment and.control measures would be to use timing of repeat burns, would be based on only practices that leave no mechanical the actual fire history of the virgin forests. scars and have minimal unnatural effects.) The objective would be to duplicate the 7. Both surface fires and crown fires long-term historic fire pattern as nearly as would be set deliberately in standing virgin possible, considering safety and ecosystem forest communities of all flammable types. size. An average of about 4200 acres per In types such as red pine, where surface year might be burned in the remaining fires were common in the past, firing could 420,000 acres of virgin forest of the Canoe be done during moderate burning condi- Area. This would put the virgin areas on tions. Combinations of spring, summer, and an overall “fire rotation” of 100 yr. Some fall burns might be used, based on lightning stands would survive many of these fires, fire frequency in these seasons, to safely and many areas would be fired at longer duplicate the natural regimes of crown, sur- or shorter intervals, as they were in nature. face, and ground fires. In poor fire seasons there might be little 8. One necessary compromise with the or no burning, while in good ones the quota natural regime would be burn size. Burning for several years could be burned. units could still vary greatly in size as they 4. Selection of areas to be burned might did in nature, but the occasional very large be based on a combination of the following: burns of 100,000 acres or more that oc- curred in the past could not be tolerated a. Location and incidence of actual because the Canoe Area is now only a lightning-caused fires in the virgin miniature of the primeval wilderness. An forests over the past few decades. upper limit on burn size must be arbitrarily b. Identification of natural firebreaks set. Several years’ quota might still occa- (large lakes and streams, swamps, sionally be burned in a single fire, if this etc.) that limited the spread of past seemed ecologically desirable, safe, and wildfires. within tolerable size limits. We do not fully c. Planning of safe ignition sequences so understand the effects of burn size, but it that a whole series of burns could be probably is a factor in wildlife habitat, seed carried out with maximum safety, us- ing natural firebreaks and previous sources, and other matters. 9. The burning of virgin forests is possi- burns as barriers to escape. ble only during fire weather sufficiently se- d. Random selection of the order of firing vere to allow fires to move-at least of major units to avoid subjective slowly. Expertise must be developed to choices based on other than ecologic, achieve natural ecological effects without logistic, or safety factors. losing control of such fires. Early in the de- 5. No cutting of trees or artificial modi- velopment of a burning program it would fication of the fuel situation would be done be necessary to work conservatively with except locally when absolutely essential to small units, large and effective natural fire- ignition or control. breaks, and moderate weather. This work 6. No road construction or use of tractors could build quickly on past research on fire FIRE AND THE NATURAL ECOSYSTEM 377 weather, fuels, and behavior, on prescribed successional stages now missing because of fires for logging-debris reduction and site fire exclusion. Eventually each should oc- preparation, and on studies of burning be- cupy a natural proportion of the landscape. neath living red pine (Ahlgren, 1959, 1960, 5. Gene pool values would be preserved 1970; Beaufait, 1962; Buckman, 1964a, b; to the maximum extent still possible. Haines and Sando, 1969; Johnston, 1971; 6. Scientific and educational values for Sando, 1969; Sando and Haines, 1972; studies of large-scale ecosystem processes Sando and Wick, 1972; Van Wagner, 1966, would be enhanced. It can be argued that 1971; and many more). As the program since man would control the times and developed, managers and researchers could places of ignition, and the size of the burns, jointly define acceptable burning weather, the system would be “unnatural.” But there necessary fire barriers, size of units, etc. would be no direct control over local fire These questions would need to be decided behavior or effects, over sources of plant on both ecological and practical grounds. propagules, or over other variables that de- With experience, some lightning fires prob- termine vegetative or animal responses. ably could be allowed under carefully de- Philosophically man would have some con- fined rules and included in burn quotas. trol, but only through conscious reintroduc- Some of the ecological and social conse- tion of the very environmental factor that quences of such a program might be as shaped the primeval vegetation. To the ex- follows : tent that fire frequency, intensity, and tim- 1. Only one natural agent, fire, would be ing duplicated the natural regime, the used, hence the ecosystem should respond effects should be natural. Major new scicbn- naturally. tific and educational opportunities would 2. Nutrient cycling rates and pathways be created because there are now no areas and accumulation rates of organic matter within the Great Lakes conifer forest where should approximate those of the primeval a large natural ecosystem that includes fire ecosystem. can be studied. New learning opportunities 3. There would be no mechanical scar- for the public would also be an important ring of the landscape, no stumps, no sawn consequence. logs or felled trees, no planted trees, and 7. There are legitimate questions about no other obvious signs of man’s activities. our ability to implement this alternative The psychological, cultural, and aesthetic with safety. However, a number of compe- values of the virgin wilderness should tent foresters and ecologists with fire ex- therefore be conserved, because the ecosys- perience believe the safety problem could tem would in fact be as nearly natural as be solved within a few years. A conserva- possible. In the words of the Wilderness Act tive approach would be to begin research LI the earth and its community of on small burning units under marginal life’ .’ . .” would be as ‘l. . . untrammeled burning conditions, and then work grad- by man . . .” as we could safely make it ually into better burning conditions and under present constraints. The land would larger units. If the method is rejected wit,h- retain “. . its primeval character and in- out such trials, then the option of maint,ain- fluence . . .” and “. . . generally appear to ing the natural ecosystem would be fore- have been affected primarily by the forces closed without testing the only ecologically of nature, with the imprint of man’s work viable alternative that faces the fire-safety substantially unnoticeable. . . .” question. 4. The vegetation mosaic produced 8. It would be necessary to alert or should include all of the virgin plant com- evacuate recreational visitors near planned munities identified by Ohmann, Ream, and prescribed burns. Closure of burning units Grigal, plus those additional early postfire might also be required at times. However, 378 HE~NSELMAN such burns would occur on only a very few and areas suitable for firing probably could days each year, and the area involved in be located somewhere almost every year. any one year would be a tiny fraction of Major opportunities to burn large units the Canoe Area (generally less than 1%). under extended drought conditions might 9. If a prescribed fire got out of hand in occur only once in 5-10 yr. When these op- severe fire weather there would be risk of portunities arose it would be desirable to loss of human lives and serious property capitalize on such weather, just as nature damage. It must be realized, however, that did. This would require assembling a large present fire-exclusion policies carry the prescribed-burning team and keeping them same or greater risks. A solution to the on standby through the drought to utilize fuels problem in Wilderness Areas is re- every good, yet safe, burning day. If burn- quired if this dilemma is to be removed. ing programs became practice, a resident 10. Eventually many highly flammable prescribed-burning specialist and a resident budworm-killed fir stands and old jack pine ecologist would be needed. forests would be consumed, and the fuels 14. A need for public understanding of situation would return to natural levels. the objectives of a prescribti-burning pro- Consumption of dead and down wood and gram is obvious. Some say the public would of standing dead trees would be good in never accept the idea of burning virgin summer and fall burns. Once fuels were re- forests in wilderness. New educational pro- duced to natural levels, control of wildfires grams that maintained the public’s concern would become easier. about wildfire, yet built ecological under- 11. Spruce budworm populations should standing and acceptance of prescribed fire, be brought down to natural levels after would be necessary. enough fir-spruce forests were burned to de- 15. Habitat suitable for native mam- prive this insect of unnatural concentra- mals, birds, reptiles, insects, and other ani- tions of mature fir. Perhaps understories of mal life would be created automatically, old budworm-killed fir in aspen-birch com- without conscious planning. Recent burns munities were an important fuel source that u-ould provide browse and fruits for moose, in nature allowed aspen-birch stands to deer, bear, hares, and small mammals. This burn easily, and thus to regenerate. This in turn would assure a food supply for tim- may be one of those “large-scale ecosystem ber wolves and other canivores. Areas of processes” we do not yet fully understand. mature forest would supply niches for pine 12. Restoring fire to the ecosystem marten, spruce grouse, and woodland cari- should reestablish fire as a natural check bou. Young aspen-birch forests would pro- on dwarf-mistletoe. Elimination of the host vide niches for ruffed grouse and beaver. (black spruce) over large areas is required Similar statements could be made for all for short periods to reduce this parasite other native species. In short, the primeval (Irving and French, 1971). ecosystem recreated, should assure the full 13. It’is often argued that a prescribed complement of wildlife naturally character- burning program would be difficult to exe- istic of the Canoe Area. Only a lack of cute logistically. Manpower, equipment, some very large burns, or perhaps also of and communications must be mobilized very extensive oId forests, might introduce quickly, because suitable weather is often habitat factors on a gross scale not present of short duration. Suitable weather also in- in the primeval ecosystem. volves the possibility that wildfires may 16. The reintroduction of fire would occur elsewhere. And sometimes there are present an exceptional opportunity for edu- only a few good burning days a year, or cation programs to help visitors understand none at all. However, in the virgin forests the complexity of natural ecosystems. there are many vegetation and fuel types, Changes in wildlife populations and in FIRE AND THE NATURAL ECOSYSTEM 379

viewing opportunities could be an impor- For we have not yet learned all that can tant aspect of such programs. be gleaned from even rather simple natural Assuming that a program of prescribed- history studies in our larger Wilderness burning and lightning fires such as that just Areas, National Parks, and de facto nntu- outlined could be implemented, one ques- ral areas. Some widely applicable concept’s, tion remains: How much time is there be- such as the increasing species diversity am1 fore the successional changes already stability of maturing ecosystems, still nce(l initiated by fire exclusion will cause fuel to be t’ested against large-scale real-world accumulations and ecological changes that examples where the natural patterns arc might preclude restoration of the natural still discernible. Without such tests, wllil(x system? Fortunately succession is slow bodies of ecological theory may rest on enough in this near-boreal ecosystem so dubious premises, or fail to account for sig- that 10-20 yr, or perhaps even 50, could nificant exceptions, and yet go unchal- elapse before fire exclusion causes irretriev- lenged. Such tests are already impossible able changes. It is true that unnaturally in most of Asia, Europe, and the eastern large areas are developing heavy fuel loads United States, where only fragments of duo to stand maturation, succession, bud- natural terrestrial ecosystems remain. I worm epidemics, local blowdowns, and suspect our large nature reserves and othcxr other events related to fire exclusion, but relatively unmodified areas of t,he giubt these things are still natural in any given still hold the key to many new ccologiral stand. What is unnatural now is mainly the principles. And it may be that only here deficiency of those young forests and recent can the full complexity of natural systcsms burns that a natural fire regime would have ever be worked out, because some procclsscs produced in the 60 yr since fire protection are visible only at full ecosystem scales. So- became effective. Yet even now, 82% of the ciety can ill afford the further erosion of virgin forest dates from the fires of such areas in either size or diversity until 1863-1864 or later (Table 4). Thus most the natural systems of the earth are umler- stands are still less than 110 yr old, and stood much better than they are today. For large areas are only 60-90 yr old. Such for- if we are to understand the genetic, physio- ests are certainly not too old to respond logical, and ecological characteristics of or- naturally to fire. Research on the Little ganisms, we must have some examples of Sioux burn is already demonstrating this the ecosystems in which they evolved. In in several vegetation types. Some red and the end such understanding may he no less white pine stands may have fir-spruce-ce- than the key to human survival. dar understories capable of supporting fires of unnatural intensity, but such under- ACKKOWLEDGMENTS stories could still be burned out with care- No field study as extensive as that report,c:d fully prescribed fires. But time is slowly here is conducted without help from many. I running out. Our opportunity to restore this gratefully acknowirdge all who aided me. My unique ecosystem will not last indefinitely. wife, Frances, and Albert Swain dcsc%rve qter-ial There is still time for research and adminis- thanks for their help and companionship in the trative trials, but they must begin soon. field, without which the data could not have betxn obtained. and for much other assistance. I also thank t.he following for help in work planning, THE VALUE OF NATURAL general support, technical advice, analyses, and ECOSYSTEMS field work : David B. King, James Morgan, Robert Lucas, Charles Cushwa, Lewis Ohmann, Robert The ecological conclusions and manage- Ream, Herbert Wright, Charlps Wick, and Edward Stone. Many members of the Superior National ment implications discussed here embody Forest have my thanks for sharing their r~ords an object lesson that should not be missed. and for logistical support. 380 HEINSELMAN

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GRIGAL, D. F., AND OHMANN, L. F. (1973). Wilder- of Superior National Forest, Duluth, Minnesota, ness Ecology: the upland plant communities U.S. Forest Service, 9 pp. (typed). of the Boundary Waters Canoe Area. Unpub- IRVING, F. D., APEDFRENCH, D. W. (1971). Control lished Manuscript, North Central Forest Experi- by fire of dwarf mistletoe in black spruce. Jorri,- ment Station and University of Minnesota. nal of Forestry 69, 28-30. GUNDERSON, H. L., AND BEER, J. R. (1953). “The IRVISO, W. S., AXD HARINGTON, C. Ii. (1973). Mammals of Minnesota.” University of Minne- Upper Pleistocene radiocarbon-dated artifatats sota Press, Minneapolis. from the northern Yukon. Science 179, 335-340. HAINES, D. A., AND SANDO, R. W. (1969). Climatic JOHNSTON, W. F. (1971). Broadcast burning slash ronditiona preceding historically great fires in favors b!ack spruce reproduction on organic, the North Central Region, Forest Service Re- soil in Minnesota. Forestry Chronicle 47( 1). search Paper NC-34,19 pp. 33-35. HEGYI, F. (1972). Dry matter distribution in jack KILGDRE, B. M. (1972). Impact of prescribed burn- pine stands in northern Ontario. Forestry ing on a squoia-mixed conifer forest. Proc. Chronicle 48, 193-197. Tall Timbers Fire Ecology Conference (1972), HEINSELMAN, M. L. (1957). Silvical characteristics pp. 345-375. of black spruce (Pz’cea mariana). U.S. Forest KILGORE, B. M., AND BRIGGS, G. S. (1972). Restor- Service, Lake States Forest Experiment St,ation ing fire to high elevation forests in California. Paper 45, 30 pp. (processed). Journal of Forestry ‘70(5), 226-271. HEINSELMAN, M. L. (1963). Forest sites, bog pro- I(OII~REK. E. V.. SR. (1964). The natural his1.or.v cesses, and peatland types in the Glacial Lake of lightning, Proc. Third Annual Tall Timbers Agassiz region, Minnesota. Ecological Mono- Fire Ecology Conference (Tallahassc~p, Florida. graphs 33, 327-374. 1964), pp. 139-180. HEINSELMAN, M. L. (1965a). Vegetation manage- KREBS. C. J. (1972). Ecology: The cxperimcntal ment in wilderness areas and primitive parks. analysis of distribution and abundance. Harper Journal of Forestry 63, 440-445. and Row. New York, 694 pp. HEINSELMAN, M. L. (1965b). Wilderness and Na- KREFTING, L. W. (1951). What, is the future of tional Park Management Goals. Journal of the Isle Royale moose herd? Trans. North Forestry 63(12), Notes and comment. Americnn Wildhfe Conference 16, 461-470. HEINSELMAN, M. L. (1969). Diary of the Canoe K~CHLER, A. W. (1964). Potential natural vegeta- Country’s landscape. Naturalist (Journal tion of the cont,erminous United States. Amcri- Natural History Society of Minnesota) 20(l), can Geographical Society, Special Puhl. 36, map 2-13. (in color) and manual, 116 pp. HEINSELMAN, M. L. (1970a). Preserving nature LEBARROS, R. K. (1939). The role of forest fires in forested Wilderness Areas and National in the reproduction of black spruce. Proceedings Parks. National Parks and Conservation Maga- of the Mirlnesota Acndemy of Science 7, 10-14. zine 44(276), 8-14. LEBARRON, l%. Ii., AND EYRE, F. H. (1939). The HEINSELMAN, M. L. (1970b). The natural role release of seeds from jack pint ronps. loui,tlal of fires in northern conifer forests. In Sym- of Forestry 37, 305-309. posium on “The role of fire in the Intermoun- LEOPOLD, A. (1921). The wilderness and its place tain West.” Intermountain Fire Research Coun- in forest rrcrrntional policy. Jownnl of Forfstw cil (Missoula, Montana, 1970), reprinted in 19, 718-721. Jatwalist 21(4), 14-23. LITTLEJOHN, 13. M., ASD PIMLOTT, D. H. (1971). HEINSELMAN, M. L. (197Oc). Landscape evolution, “Why wilderness?” Xcw Press, Toronto, Ontario. peatland types, and the environment in the Loucq 0. L. (1970). Evolution of diversity, effi- Lake Agassiz Peatlands Natural Area, Minne- ciency, and communit,y stability. Americafl sota. Ecological Monographs 40, 235-261. Zoologist 10, 17-25. HEINSELMAN, M. L. (1971). Restoring fire to the M.4c ARTHUR, R. H. (1958). Population ecology ecosystems of the Boundary Waters Canoe Area, of some warblers of northeastern coniferous Minnesota. Proc. Tenth Annual Tall Timbers forests. Ecology 39, 599-619. Fire Ecology Conference (Fredericton, N.B., MARSCI-INER, F. J. (1930). Original forests of Min- 1970), 9-23. nesota. A map compiled from General Land HEINSELMAN, M. L., AND ROE, E. I. (1963). A Office survey notes, on file in the U.S. Dept. record of some Pleistocene trees and shrubs Agriculture, Washington, D.C., and North Cen- from Itasca County, Minnesota. Forest Science tral Forest Experiment Station, St. Paul, Minne- 9, 336-337. sota. 45 x 53 in., in color, unpublished. HIGGINS, S. M. (1908). Additional area to the MAISSCROW, D. K. (1935). Fire as a necessary proposed Lake Superior National Forest, Min- factor in the perpetuation of white pine, Journal nesota. Unpublished report in historical files of Forestry 33, 373-378, 382 HEINSELMAN

MARTIN, P. S. (1973). The discovery of America. SANDO, R. W., AND HAINES, D. A. (1972). Fire Science 179, 969-974. weather and behavior of the Little Sioux fire. MARTIN, R. J. (Ed.). (1934a). Climatic summary North Central Forest. U. S. Forest Service Re- of the United States, Section 46-Southeastern search Paper NC-76, 6 pp. Minnesota. U.S. Dept. of Agriculture, Weather SANDO, R. W., AND WICK, C. H. (1972). A method Bureau, 26 pp. of evaluating crown fuels in forest stands. North MARTIN, R. J. (Ed.). (1934b). Climatic summary Central Forest. U.S. Forest Service Research of the United States, Section 44-Northern Paper NC-84,lO pp. Minnesota. US. Dept. of Agriculture, Weather SCOTTER, G. W. (1971). Wildfires in relation to Bureau, 27 pp. the habitat of barren-ground caribou in the MAYCOCK, P. F., AND CURTIS, J. T. (1960). The taiga of northern Canda. Proc. Tenth Annual phytosociology of boreal conifer-hardwood Tall Timbers Fire Ecology Conference (Frede- forests of the Great Lakes region. Ecological ricton, N.B., 1970), pp. 85105. Monogruphs 30(l), l-35. SIMS, P. X. (1970). Geologic map of Minnesota. MECH, L. D. (1970). “The Wolf: The Ecology Bedrock geology. Minnesota Geological Survey, s nd Behavior of an Endangered Species.” Misc. map series, Map M-14. American Museum of Natural History, Natural SPURR, S. H. (1954). The forests of Itasca in the History Press, Garden City, New York. nineteenth century as related to fire. Ecology MECH, L. D. Wolf numbers in the Superior Na- 35, 21-25. tional Forest in Minnesota. In press. U.S. Forest SVOBODA,F. J., AND GULLION, G. W. (1972). Prefer- Service, Research Paper. ential use of aspen by ruffed grouse in northern MECH, L. D., AND FRENZEL, L. D., JR. (Eds.). Minnesota. Journal of Wildlife Management (1971). Ecological studies of the timber wolf 36(4), 1166-1180. in northeastern Minnesota. U.S. Forest Service SWAIN, A. M. (1972). A fire history of the Research Paper NC-52, 62 pp. Boundary Waters Canoe Area as recorded in MIROV, N. T. (1967). “The Genus Pinus.” Ronald lake sediment. NaturaZist (Journal Natural Press, New York. History Society of Minnesota) 23(3,4), 24-31. MUTCH, R. W. (1970). Wildland fires and ecosys- U.S. DEPT. OF AGRICULTURE. (1941). Climate and tems-a hypothesis. Ecology 51, 1046-1051. Man. U.S. Dept. of Agriculture Yearbook, 1941, NUTE, G. L. (1945). “The Voyageur’s Highway.” 1248 pp. Minnesota Historical Society, St. Paul, VAN RAALTE, G. D. (1972). Do I have a budworm- Minnesota. susceptible forest? Forestry Chronicle 48, OHMANN, L. F., AND REAM, R. R. (1971a). Wilder- 190-192. ness ecoIogy : a method of sampling and sum- VAN WAGNER, C. E. (1966). Three experimental marizing data for plant community classifica- fires in jack pine slash. Canada Department tion. U.S. Forest Service Research Paper NC-49, of Forestry, Publ. 1146,22 pp. 14 PP. VAN WAGNER, C. E. (1971). Fire and red pine. OHMANN, L. F., AND REAM, R. R. (1971b). Wilder- Proc. Tenth Annual Tall Timbers Fire Ecology ness ecology: virgin plant communities of the Conference (Fredericton, N.B., 1970), pp. 211- Boundary Waters Canoe Area. U.S. Forest Ser- 219. vice Research Paper NC-63,55 pp. VOGL, R. J., AND BECK, A. M. (1970). Response PEEK, J. M. (1972). Adaptations to the burn: of white-tailed deer to a Wisconsin wildfire. moose and deer studies. Naturalist (Journal American Midland Naturalist 84, 269-272. Natural History Society of Minnesota) 23(3,4), WHITTAKER, R. H. (1970). ‘LCommunities and Eco- 8-14. systems.” Macmillan, New York. ROE, E. I. (1963). Seed stored in cones of some WRIGHT, H. E., JR. (1968). The roles of pine and jack pine stands, northern Minnesota. U.S. spruce in the forest ‘history of Minnesota and Forest Service Research Paper LS-1, 14 pp. adjacent areas. Ecology 49,937-955. ROSENDAHL, C. 0. (1948). A contribution to the WRIGHT, H. E., JR. (1971). Retreat of the Lauren- knowledge of the Pleistocene flora of Minnesota. tide Ice Sheet from 14,000 to 9,000 years ago. Ecology 29, 284-315. Quarternary Research 1, 316-330. ROWE, J. S. (1959). Forest regions of Canada. WRIGHT, H. E., JR., AND WATTS, W. A. (1969). Canada Dept. of Northern Affairs and Natural Glacial and vegetational history of northeastern Resources, Forestry Branch, Bull. 123, 71 pp. Minnesota. Minnesota Geological Survey, Spe- SANDO, R. W. (1969). Prescribed burning weather cial Publication Series SP-11, 59 pp. in Minnesota. U.S. Forest Service Research YEATMAN, C. W. (1967). Biogeography of jack Paper NC-28 8 pp. pine. Canadian Journal of Botany 45, 2201-2211.