Fire and Other Factors Controlling the Big Woods Vegetation of Minnesota in the Mid‐Nineteenth Century

Bearing—tree data from the original land—survey records of 1847—1850 were used to reconstruct the vegetation of the Big Woods and adjacent areas along the prairie—woodland border in south—central Minnesota. The characteristic tree taxa of the Big Woods were elm (Ulmus), basswood (Tilia americana), sugar maple (Acer saccharum), ironwood (Ostrya virginiana), bitternut hickory (Carya cordiformis), butternut (Junglans cinerea), and ash (Fraxinus). The most common tree was elm, which comprised 27% of the bearing trees. A buffer zone of fire—tolerant oaks and aspen generally lay between the Big Woods and prairie. The width of this zone depended on topography and on the presence of additional firebreaks, which in places formed sharp boundaries between the Big Woods and oak—aspen. The prairie—woodland border was characteristically a sharp boundary along firebreaks (water bodies and physiographic breaks). In some places very effective firebreaks formed sharp boundaries between prairie and the Big Woods, with no intervening oak—aspen zone. The vegetation was most strongly correlated with the fire—probability pattern, which was a function of both abiotic and biotic factors. Soils influenced the probability of fire, but they also were the major factor controlling the vegetation within areas of similar fire probability. Soil drainage was the most important factor controlling vegetation within the units of the overall pattern. Because the locations of firebreaks and the existing pattern of vegetation controlled the fire probability pattern, sites with virtually identical physical characteristics supported qualitatively different types of persistent or stable vegetation.