PTERIDOPHYTES
Daniel F. Brunton
BIODIVERSITY CHANGE
With the end of the Wisconsin deglaciation in the Mixedwood Plains Ecozone area ca.13,000 - 12,000 years BP (Dyke and Prest 1987a), subarctic/ boreal conditions dominated the uplands. This condition continued until ca. 10,000 years BP (McAndrews et al. 1987). The ecozone was part of a huge, transcontinental area of boreal/subarctic habitat dominated by extensive northern coniferous forest, peatland and early successional hardwood forest cover. Extensive boreal grasslands extended across at least the Great Lakes portion of the ecozone towards the end of this period (Catling and Brownell 1995). Pteridophytes now with primarily northern and western distributions were likely common (or at least more common) in the ecozone than they are today. These would include Ground-cedar (Diphasiastrum complanatum (s. str.), Spikemoss (Selaginella selaginoides), Northern Clubmoss (Huperzia selago), Smooth Woodsia (Woodsia glabella) and Moonwort (Botrychium lunaria). Several of these are found only in boreal/subarctic habitat relicts today.
For much of the period (ca. 11,000 - 9,500 years BP) virtually all of the area east of the Frontenac Axis was inundated by the post-glacial marine incursion known as the Champlain Sea (Dyke and Prest 1987b). It filled the massive bedrock depression which had been created by the weight of the glacial ice. By ca. 9,000 years BP isostatic rebound reduced the Champlain Sea into the shallow, freshwater Lake Lampsilis as southern hardwood and Mixedwood habitat spread from southern refugia into the lower Great Lakes area . Pteridophytes with primarily eastern ranges likely first entered the Mixedwood Plains Ecozone during this initial period of recolonization, including such species as River Quillwort (Isoetes riparia), Massachusetts Fern (Thelypteris simulata) (Fig.PT-1) and Chain-fern (Woodwardia virginica).
Subsequent vegetation and faunal recolonization of the ecozone was largely from the south and southwest (Appalachian and Mississippi Valley regions). This included prairie and savannah flora invading from the southwest during the warmer, drier hypsithermal period which dominated eastern Canada and the Great Lakes region between 7,000 and 4,000 years BP. The intrusion of western biota occurred in a narrow band called the "Prairie Peninsula" (Catling et al. 1992) extending eastward north of Lake Erie into the area north of central Lake Ontario. It is likely that a number of the now-localized southern species were more widespread during the hypsithermal, including Goldies Fern (Dryopteris goldiana)(Fig.PT-2), Glade Fern (Diplazium pycnocarpon), Creeping Fragile-fern (Cystopteris protrusa) and Broad Beech-fern (Phegopteris hexagonoptera).
Habitats transitional between the boreal/subarctic environment of the early post-glacial period and the deciduous and mixed forest habitats of the hysithemal period became established as the climate cooled. Contemporary conditions and habitats were established by ca. 3,500 years B.P. (McAndrews et al. 1987). Common species of these habitats today include Woodland Horsetail (Equisetum sylvaticum), Staghorn Clubmoss (Lycopodium clavatum), Maidenhair Fern (Adiantum pedatum), Marsh Fern (Theylpteris palustris), Evergreen Woodfern (Dryopteris intermedia) (Fig.PT-3), Marginal Shieldfern (Dryopteris marginalis), Polypody (Polypodium virginianum) and Christmas Fern (Polystichum acrostichoides).
