Landform development and coupled vegetation succession along Gull Point, Presque Isle Pa, a barrier-spit system along the southeastern Lake Erie margin

The Presque Isle peninsula is a compound barrier-spit system perched atop a recessional moraine along the southeastern Lake Erie coast. Gull Point, the system's distal terminus, has grown to an extent of approximately 0.6 km2 since the early 1900s, driven by a shift in local littoral hydrodynamic regime following upstream installation of breakwaters. The general evolutionary model for spit development here is one of punctuated landform growth to the east by lateral accretion, interspersed with erosional events and the recurving of ridges toward the backbarrier. Vegetation communities developing by primary succession appear to be delineated into four temporal phases extending back to at least the 1950s, roughly defined by pronounced erosional demarcations of topographic prominence. We are now exploring this premise via transect/quadrat surveying and increment core dating of eastern cottonwood cohorts on dune ridges separated by swales and lagoons. The youngest (distal) phase east of a 1993 shoreline is mostly herbaceous, suggesting woodlands are initially slow to establish. However, winter-season surveys of this zone, when a shorebird breeding sanctuary is open the public, suggest cottonwoods and willows recruit here every year. Core-dated cottonwoods along the youngest pre-1993 ridges are between 18 and 26 years at breast height (1.37 m), but are generally <20 cm in diameter. Riverfront cottonwoods of this size are typically half this age. We suspect that not only is seedling survival precarious and episodic on these exposed surfaces, but growth of young trees is slow. We speculate that surveying along progressively older proximal ridges to the west may reveal decreasing stress on the vegetation as landforms have become longer established and more protected. However, the arcuate ridge-and-swale topography of the former recurved backbarrier is now prominently exposed lake-ward, and erosion of forested shore-perpendicular ridges is commonplace. New vegetative colonization along this eroding shore appears transient at best, given retreat rates up to approximately 10 m/yr, which threaten to breach the spit entirely in select locations.