FLOOD PLAIN EVOLUTION, WETLAND DEVELOPMENT AND PLANT CULTIVATION IN THE SAGINAW BAY REGION OF MICHIGAN: EVIDENCE FOR CONTINUITY IN THE MANAGEMENT OF DOMESTICATED CUCURBITA PEPO FROM THE LATE ARCHAIC THROUGH MIDDLE WOODLAND PERIODS

Research in the Saginaw Bay region of Michigan reveals that Cucurbita (squash) has been used locally by humans since at least 3.8 kyBP (uncalibrated), and that by 2.8 kyBP domesticated varieties of Cucurbita pepo were introduced and cultivated on flood plains or wetlands along the Saginaw River. Geoarchaeological evidence at and near archaeological sites suggests that Late Archaic and Middle Woodland-aged domesticated C. pepo varieties probably grew in semi-cultivated, ruderal garden plots and may have formed free-living stands on flood plains and wetlands surrounding the sites. If so, these may represent one of the earliest human-introduced, invasive plants in North America.

Decades of geological and archaeological research at Late Archaic through Middle Woodland occupation sites along the Saginaw River near Saginaw, Michigan, reveals a complex floodplain stratigraphy of intercalated wetland, alluvial, lacustrine and cultural horizons. This record documents how changes in wetland resources and configuration effects human occupation, provides insights into the place of wild and domesticated plants in the floodplain ecology, and reveals how human usage of wetland settings and resources varied through time and cultural periods. Uncarbonized seeds of domesticated C. pepo were recovered at two different locales from natural (non-cultural) wetland deposits adjacent to archaeological sites and buried up to 3 m deep within the alluvial sequence. The sedimentological context for domesticated C. pepo seeds indicates they were deposited as flood detritus within the wetlands, suggesting that squash grew locally in tended or naturalized stands on or adjacent to the flood plain. Direct AMS dates on two seeds from two different locales are 2820+/-40 BP (Beta 150203) and 1830 +/- 40 BP (Beta – 215173), uncalibrated, which indicate that the wetlands were long-lived and suggest a similar pattern of squash usage spanned the Late Archaic and Middle Woodland cultural periods. The age of a shallow, near-surface Middle Woodland pit overlying the deepest and oldest of the seeds indicates that at least 2 m of sediment buried part of the wetlands prior to 1.8 kyBP. The burial was probably related to increased alluviation during a post-2 kyBP transgression of Lake Huron, and may be climate-related.