Geology, soils and vegetation of Blackhawk Island, Wisconsin.

Blackhawk Island, in the Wisconsin River in SW Wisconsin, supports a wide variety of forest communities on several soil types. The soils form a gradient of moisture and N availability. Pines (Pinus strobus, P. resinosa) are dominant on sandy soils with low N mineralization and nitrification; oaks (Quercus borealis, Q. alba) are dominant on sandy clay-loams and silt loams with moderate N mineralization and nitrification, and sugar maple Acer saccharum is dominant on silty clay-loams with high N mineralization and nitrification. Species replacement along this gradient results in an increase in continuum index that is strongly related to the increase in N mineralization, nitrification, silt + clay content and P content of the soils. Two communities not on this gradient are: 1) aspen Populus grandidentata on plowed silt loam with low N mineralization and nitrification and 2) hemlock Tsuga canadensis on organic soil with low N mineralization and nitrification.-from Authors