Using original land survey records and soils to map the pre-settlement distribution of tamarack in southeastern Wisconsin

Background/Question/Methods Tamarack (Larix laricina) is an indicator of some of the highest quality and least disturbed wetland communities remaining in the Southeast Glacial Plains (SGP) Ecological Landscape of Wisconsin. The General Land Office’s (GLO) original witness tree records obtained between 1833 and 1852 show that tamarack was one of the most common and dominant trees in the swamps of southern Wisconsin. We have developed a map of the pre-settlement distribution of tamarack communities in the SGP using the GLO witness tree data and the hydric soils (a proxy for wetland delineation) data from the Soil Survey Geographic Database (SSURGO). Using ArcGIS, we examined the distribution of tree species using the center, mid-point and line meander survey points in the SGP.  If any of the witness trees falling within a hydric soil polygon were tamarack, we assigned that polygon to a tamarack swamp plant community type. We estimated the total acreage of wetland that supported tamarack swamp in the pre-settlement landscape by extrapolating the percentage of tamarack occurrence in those hydric soil polygons having at least one witness tree, to all hydric soils.
Results/Conclusions Roughly 47% of the SSURGO hydric soil polygons in the area we studied had GLO witness tree records within their boundaries, and therefore a record that could be used to assign their pre-settlement plant community.  Our analysis estimates that tamarack communities once covered up to 310,000 acres in the SGP, a potential overestimation.  Another map of the pre-settlement vegetation of Wisconsin constructed from GLO records (Finley 1976) likely underestimates the acreage of tamarack by 30,000 acres due to a more subjective interpretation of the data.  Current Wisconsin Wetland Inventories found that 47,000 acres of tamarack communities remain in today’s SGP landscape, a loss of more than an 80%.  Landscape analysis comparing the current and presettlement distribution of tamarack will help us determine factors that contributed to the extensive loss of tamarack from the past to present and those factors that may cause further decline in the future.