INTERACTION OF SOIL TYPE, CLIMATE, FIRE, AND VEGETATION: HISTORY OF THE NORTHWESTERN WISCONSIN SANDPLAIN

We analyzed sediment cores from Little Round (LR) and Hell Hole (HH) lakes in northwestern Wisconsin to study the interaction of soil, climate, fire, and vegetation. These sites are both seepage lakes, on sandy soil. Each lake has an area of less than 10 ha and is more than 8m deep. The primary physical difference between the sites is that LR is located on slightly more excessively well-drained sands.

Oak and prairie forb pollen percentages are relatively high (10-40% and 3-10% respectively) from 6000 to ~2500 cal. yr. BP, consistent with oak savanna or woodland dominating the area. The charcoal record is similar at the two sites during this period with low charcoal accumulation rates (CHAR) ranging from ~0-10 particles/cm²/yr. Charcoal accumulation rates during this period may represent frequent, small fires on an unproductive, dry landscape, maintaining savanna/woodland vegetation.

After this period, more mixed pine-oak vegetation developed with perhaps a slight increase in frequency of intense fires. By 1600 years ago, oak declined further, especially at HH, where the highest CHAR is found (30/cm²/yr). Red/jack pine pollen increased and white pine was generally low at both sites between 1600-800 cal. yr. BP. During this period sporadic CHAR peaks (8-30/cm²/yr) are consistent with a fairly dense canopy of pines maintained by occasional stand destroying fires.

The most recent 1000 years had a large increase in white pine pollen with low overall charcoal deposition. These findings are typical of other sites on the sand plain, suggesting that the cooler/wetter conditions of the LIA (Little Ice Age) may have driven a regional increase in white pine. The post-European settlement period records an increase in ragweed and oak (especially at LR) pollen near the surface. Higher oak pollen abundances are likely due to land use changes associated with European settlement (logging and slash fires). However, these pollen assemblages are not similar to any of our 31 pre-European pollen assemblages on the sand plain, but closely resemble the pollen assemblage of samples from >2500 cal. yr. BP.