PARENT SESSION
Oral Session #6: Disturbance Ecology of Forests: Fire, Patterns. Presiding: R. DeFries.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas F.
Late Holocene and contemporary change in jack pine forests in dune-fields along the upper Great Lakes.
Loope, Walter1, Pavlovic, Noel2, Carey, Lawrence3, 1 2 3
ABSTRACT- Beach ridge studies have recently documented quasi-periodic, climate-driven changes in levels of the upper Great Lakes throughout the past 5000 years. The many paleosols that crop out within dune-fields along the Lakes attest to periodic establishment and burial of jack pine (Pinus banksiana) and white cedar (Thuja occidentalis) forests. Radiocarbon dating of these paleosols appears to link their establishment and extinction with episodes of lake-level (and sand supply) change on ~150 year return periods. Using time sequences of air photos and increment cores, we documented forestation by jack pine in six major coastal dune fields during the first half of the 20th century, an apparent ~150-year trough in levels of the upper Lakes. Quantitative sampling of forest structure and understory in two dune-fields with representative jack pine forests revealed high species richness and absence of typical fire-adapted species. 20th century establishment and extinction of jack pine stands on lakeshore ridge and swale sequences is also consistent with 20th century lake level history. While multi-decade vegetation change on foredunes (mediated by ~30 year periodicities of lake-level and sand-supply change) has been well studied, the structure and dynamics of jack-pine forests within coastal dunes is not well known. Contemporary forestation within coastal dunes of the upper Lakes mirrors similar multiple successional pathways that occurred repeatedly during century-long episodes of sand starvation throughout the late Holocene.
KEY WORDS: dunes, jack pine, Holocene, Great Lakes