Historic Vegetation

The use of General Land Office survey information in reconstructing historic forests

The maps of historic vegetation on this website, reconstructed from General Land Office survey records, are a reliable depiction of the range of forest composition in the northern Lake States over a long time period, with the exception of areas inside the boundaries of fire-susceptible ecosystems. This statement is based on evidence of: (1) the stabilized migration of forest species into the northern Lake States about 3,000 to 3,500 years ago (Davis 1981, Davis et al. 1993), (2) the extremely old age of forests in mesic hemlock-hardwood ecosystems (Frelich 1995), (3) the limited variety of possible community types and successional pathways within fire-susceptible ecosystems, (4) the affinity of certain forest species to specific geologic features due to moisture-nutrient-competition interactions that prevented extreme change in forest composition, and (5) the persistence of vegetation even given minor climatic fluctuations (Pielou 1991).

The original land survey by the General Land Office (GLO) provides the earliest systematically recorded information on forest composition in the Lake States. The GLO surveys began in 1826 in Michigan, 1832 in Wisconsin, and 1847 in Minnesota (Stearns 1996). GLO surveyors noted tree species and their diameters along section lines, providing a grid of transects approximately one mile apart. Locations of recently burned areas, windthrows, beaver impoundments, rivers and streams, wetlands, existing settlements, trails and roads, and agricultural potential of soils were also recorded, and generalized maps of timber types and soil quality were prepared.

GLO records have been used for many years to provide information on tree species composition, diameter size distribution, and disturbance patches in the pre-European settlement forests of the Lake States (Cottam 1949, Stearns 1949, Bourdo 1956, 1983, Cottam and Curtis 1956, Curtis 1959, Loucks 1983, Whitney 1986, 1987, Frelich 1995). Bourdo (1956) provides an extensive review of problems associated with the use of GLO information for quantitative analyses, and describes statistical tests used to determine if the data is biased. Surveyors' preferences for select species have been found at some locations; a few surveyors favored beech for marking as bearing trees because the bark did not have to be removed, while others preferred loose-barked trees (Bourdo 1956). Biases in species selection can usually be detected, whereas biases in diameter estimates cannot. There are a few notorious instances in which a surveyor fabricated data. Such areas were identified by comparing GLO notes on stream crossings and wetlands with the actual locations of those features, and problem areas were later resurveyed. In spite of some biases at some locations, GLO data are still considered useful by the scientific community because biases are not widespread or significant enough to render the information inaccurate if interpreted at the proper spatial scale (Almendinger 1997, Bourdo 1956, 1983), and the degree of bias can be evaluated for most applications.

While information derived from GLO notes has long been used to construct maps of the historic forest, critics of such maps contend that conditions depicted merely represent those that existed at a single point in time, hence have limited value in comprehending conditions dating further back in time. We regard this logic specious in several respects, based on evidence presented in the following discussion.

Maps generated from GLO data are based on a single measurement of forest conditions during the early to mid-nineteenth century. However, their interpretation must be based on considerations of periodicity, location, and overall amount of change in forested ecosystems in relationship to (1) climatic fluctuations, (2) natural disturbance regimes, and (3) physical substrates that direct or limit change. Perhaps best stated by Frelich (1995), "The presettlement data can be interpreted as a stable baseline and used to evaluate changes in the landscape caused by humans. Such an evaluation is possible because the geographic distributions of major tree species, such as maples, pines, and oaks, have only changed by 4-10 km/century over the last 10,000 years and have changed little in the last 3,000 years." Webb et al. (1993), Davis et al. (1993), and Brubaker (1975) corroborate these conclusions regarding the effects of climate change on tree species distribution.

While distributions of forest species became stable at least 3,000 years ago in the Lake States, the locations of some species, and their successional states, have varied within the region over time. These finer-scaled changes in distribution are brought about by minor climatic fluctuations like the Little Ice Age; natural disturbance regimes of fire, wind and flooding; and population cycles of insects and disease-causing organisms. These agents of change do not impact all ecosystems equally. Certain conditions of the physical environment make some ecosystems more susceptible to rapid changes than others; this susceptibility depends on landform controlled soil, topographic, and hydrologic conditions, and the way in which landform juxtaposition contributes to or limits the spread of disturbance (Swanson et al. 1988, Host et al. 1987). Physical factors often act as boundaries that contain certain kinds of disturbance, and these boundaries are relatively invariant over centuries. Biological conditions are also linked to the rate of change in species and successional patch locations because of species-specific reproductive strategies and life expectancy.

Forest type distributions are correlated with conditions of the physical substrate, with pine on "coarse-textured soils derived from outwash and ice-contact deposits," which in turn "promoted a vegetation type which was extremely susceptible to fire" (Whitney 1986). Northern hardwood and hemlock-hardwood forests are found on fine to medium textured till soils on glacial moraines. These requirements of forest species for certain moisture and nutrient conditions precluded widespread or drastic changes in composition of the original forests in the Lake States area; pines were always restricted to droughty sandy landforms, hemlock-hardwood forests to nutrient-rich glacial till, and wetland conifers to areas with suitable hydrologic conditions.

Changes in the location of forest species and their successional patches are more apparent when viewed at a landscape scale within the context of the regional setting. At this scale, typically measured in tens of thousands of acres, mesophilic, wind-driven ecosystems were composed mostly of long-lived tree species (e.g., sugar maple, yellow birch, hemlock). Changes within these forests were caused primarily by fine scale blowdowns of one-tenth to one-quarter acre in size; rarely, catastrophic winds woulddemolish a larger patch averaging a few hundred acres in size (Frelich and Lorimer 1991, Canham and Loucks 1984). Long-lived species regenerated in the small windthrow gaps (Davis et al. 1993, Frelich et al. 1993), and short-lived species only gained temporary dominance in the rare large openings. Thus, these "asbestos" forests exhibited a repeating yet shifting steady state of fine-scaled mosaics of species whose overall proportions remained essentially constant (Borman and Likens 1979), and which were greatly dominated by long-lived forest species.

At the same spatial scale, pyrophilic, fire-regulated ecosystems on dry, nutrient-poor landforms supported both long-lived tree species (e.g., white and red pine) and short-lived species (e.g., jack pine, aspen, white birch). Locations of forest patches in these systems changed over time due to disturbances from wildfire and Native American sources; changes were more frequent and dramatic than in the mesic hemlock-hardwood forests. Cover types were replaced in patches of hundreds to thousands of acres within several decades to a century or more. Vegetation types were variously openlands, barrens, or dense coniferous forest depending fire frequency and the length of time elapsed since fire disturbance. Age classes and patch configurations generally followed an ecosystem-dependent periodicity and spatial pattern associated with the fire-dominated disturbance regimes. The natural condition of fire-regulated systems was therefore a state of disequilibrium for individual areas, with representation of the entire range of successional states present in the larger regional area.

Frelich (1995) estimated that before settlement, 89% of the northern hardwoods, and 55% of the mixed white and red pine, spruce-fir-birch, and oak-hickory forests of the Lake States were in an old growth condition. These estimates were based on an assumption that old-growth conditions were attained at an age of 120 years or greater for long-lived communities such as northern hardwoods, and 80 years for short-lived species such as aspen, birch, and jack pine. The very old age of the majority of northern hardwood ecosystems indicates that not many short-lived species were present, and that overall species composition and age-class distribution would have been relatively stable. This contrasts with fire-dependent ecosystems such as spruce-fir, aspen-birch, and jack pine, which consisted of forests characterized by a more even age class distribution.

Pielou (1991) introduced the concept of ecological inertia and cited this phenomenon as an additional factor leading to the relative stability of forest communities, even during minor climatic fluctuations. She defined ecological inertia as the lag in forest change due to plant persistence, with established communities physically preventing encroachment by other species that were better adapted to changed climatic conditions. She asserted that vegetation is slow to respond to climatic change, hence a short-duration change may not produce a response in species' geographic distribution simply because species would not have time to migrate. This delayed response of vegetation to short-term climatic change may explain why the biogeography of forest trees changed steadily following Pleistocene glaciation, without any reversals in the direction of the change. She noted that, in addition to ecological inertia, natural selection for progeny adapted to changed conditions also resulted in stability.

In summary, the maps of historic vegetation found on this website are a reasonable reflection of forest composition in the northern Lake States over a long time period, with only minor fluctuations in the location of short-lived forest types within mesophilic ecosystems, and changing yet predictable patterns within pyrophilic ecosystems. Integrating this information on past natural vegetation with other knowledge about the biological and physical environment, and disturbance regimes, will allow us to develop spatially explicit estimates of the characteristic rate of natural change, technically termed the dynamics of homeorhetic stability (Reice 1994, O'Neill et al. 1986), that formerly distinguished and influenced the landscape and local ecosystems of the Lake States.

References

Almendinger, J.C. 1997. Minnesota Bearing Tree Data Base. Minnesota Department of Natural Resources Biological Report No. 56.

Bourdo, E.A., Jr. 1956. A Review of the General Land Office survey and of its Use in Quantitative Studies of Former Forests. Ecology 37:754-768.

Bourdo, E.A., Jr. 1983. The Forest the Settlers Saw. Pp. 3-16. In: S.L. Flader, ed. The Great Lakes Forest: An Environmental and Social History. University of Minnesota Press, Minneapolis, MN. 336 p.

Borman, F.H. and G.E. Likens. 1979. Pattern and Process in a Forested Ecosystem. 253p. Springer-Verlag, New York.

Brubaker, L.B. 1975. Postglacial Forest Patterns Associated with Till and Outwash in Northcentral Upper Michigan. Quaternary Research 5: 499-527.

Canham, C. D., and O. L. Loucks. 1984. Catastrophic windthrow in the presettlement forests of Wisconsin. Ecology 65(3):803-809.

Cottam, G. 1949. The Phytosociology of an Oak Woods in Southwestern Wisconsin. Ecology 30:271-287.

Cottam, G., and J.T. Curtis. 1956. The use of Distance Measures in Phytosociological Sampling.  Ecology 37:451-460.

Curtis, J.T. 1959. The Vegetation of Wisconsin - An Ordination of Plant Communitites. The University of Wisconsin Press, Madison, WI.

Davis, M.B. 1981. Quaternary history and the stability of forest communities. Pp. 132-153. In: West, D.C., H.H. Shugart, and D.B. Botkin, eds. Forest Succession: Concepts and Application.  New York: Springer-Verlag.

Davis, M. B., S. Sugita, R. R. Calcote, J. B. Ferrari, and L. E. Frelich. 1993. Historical development of alternate communities in a hemlock-hardwood forest in northern Michigan, U.S.A. Pp. 19-39. In: P. J. Edwards, R. M. May, and N. R. Webb, N.R., editors. Large-Scale Ecology and Conservation Biology: The 35th Symposium of the British Ecological Society with the Society for Conservation Biology. University of Southampton. Boston, MA: Blackwell Scientific Publications.

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Frelich, L. E. 1995. Old forest in the Lake States today and before European settlement.   Natural Areas Journal 15:157-167.

Frelich, L. E., and C. G. Lorimer. 1991. Natural disturbance regimes in hemlock-hardwood forests of the Upper Great Lakes Region. Ecological Monographs 61(2):159-162.

Frelich, L.E.; Calcote, R.R.; Davis, M.B.; Pastor, J. 1993. Patch formation and maintenance in an old-growth hemlock-hardwood forest. Ecology 74(2):513-527.

Host, G.E.; Pregitzer, K.S; Ramm, C.W.; Hart, J.B.; Cleland D.T. 1987. Landform mediated differences in successional pathways among upland forest ecosystems in northwestern Lower Michigan. Forest Science 33:445-457.

Loucks, O.L. 1983. New Light on the Changing Forest. Pp. 17-32. In: S.L. Flader, ed. The Great Lakes Forest: An Environmental and Social History. University of Minnesota Press, Minneapolis, MN. 336 p.

O'Neill, R.V., D.L. DeAngelis, J.B. Waide, and T.F.H. Allen. 1986. A hierarchical concept of ecosystems. Princeton University Press, Princeton, N.J.

Pielou, E.C. 1991. After the Ice Age: the return of life to glaciated North America. The University of Chicago Press.

Reice, S.R. 1994. Nonequilibira Determinants of Biological Community Structure. American Scientist. Volume 82. Pp 424-435.

Runkle, J. R. 1982. Patterns of disturbance in some old-growth mesic forests of eastern North America. Ecology 63(5):1533-1546.

Stearns, F. 1949. Ninety years change in a northern hardwood forest in Wisconsin. Ecology 30(3):350-358.

Stearns, F. 1995. History of Wisconsin's northern forests and the pine barrens. In: E. A. Borgerding, G. A. Bartelt, and W. M. McCown, eds. The Future of Pine Barrens in Northwest Wisconsin: A Workshop Summary: proceedings of the workshop; 1993 September 21-23; Solon Springs, WI. PUBL-RS-913-94. Madison, WI: Wisconsin Department of Natural Resources: 4-6.

Swanson, F.J.; Kratz, T.K.; Caine, N.; Woodmansee, R.G. 1988. Landform effects on ecosystem patterns and processes. BioScience 38:92-98.

Webb, T., III; Bartlein, P.J.; Harrison, S.P.; Anderson, K.H. 1993. Vegetation, lake levels, and climate in eastern North America for the past 18,000 years. Pp. 415-467. In: Wright, H.E, Jr..; Kutzbach, J.E.; Webb, T., III; Ruddiman, W.F.; Street-Perrot, F.A.; Bartlein, P.J., eds. Global Climates since the Last Glacial Maximum. Minneapolis, MN: University of Minnesota Press.

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Whitney, G. G. 1987. An ecological history of the Great Lakes forest of Michigan. Journal of Ecology 75:667-684.

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