Abstract
Vegetation patterns in peatlands suggest autogenic peatland development and hydrological processes are controlling factors in peatland evolution. These processes regulate vegetation ordination by influencing pH and nutrient availability at the peat surface. Geophysical studies in Caribou Bog, a 2200-hectare peatland in central Maine, indicate a close correlation between underlying geologic deposits and dominant vegetation type. The location of pools within the bog also appears to be related to subsurface geologic materials. Electrical resistivity imaging along a 1 km transect across the central unit of Caribou Bog resolved underlying lake sediment and glacio-marine clay thickness, as well as variability in depth to glacial till. Ground penetrating radar precisely defined the organic-rich lake sediment, the glacio-marine interface, and elevated till surfaces where peat thickness is less than 10 m. Direct verification of peat and lake sediment thickness, in addition to samples of the glacio-marine and till deposits, constrained the geophysical interpretation. Wooded heath (WH) interspersed with occasional Sphagnum lawn occurs where lake sediment and glacio-marine clay accumulation is thickest. Abrupt thinning of both layers (such that peat rests directly on till in places) correlates with a sharp transition to shrub heath dominated vegetation. A major open pool area located within the WH coincides with a localized sandy mineral soil-lake sediment contact at the base of the bog. The geophysical data suggest the underlying double basin system influences peatland development and dictates vegetation patterning. Limited groundwater elevation data suggest that sub-organic sediment stratigraphy mapped with geophysics regulates water levels at the peat surface, exerting a control on vegetation patterning. The major pool area, located between the basins, appears to reflect isolation of stagnant water at a point where peat development is incomplete and thus suggests that pools exist concurrent with peatland formation.
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