Fire, vegetation, and water-level history from the Stockton Island tombolo: Apostle Islands National Lakeshore

Booth, Robert; Huff, Matthew; Bebout, Julia; Lynch, Elizabeth; Schuurman, Gregor

doi:10.36967/nrr-2284385

Great Lakes Barrens are a rare ecosystem type occupying sandy coastal settings of the upper Midwest and are dominated by scattered pines and an open understory of dune species. These ecosystems historically experienced periodic fires, but quantitative information on past fire regimes is sparse. Historical photographs from Great Lakes Barrens and associated red pine forest on Stockton Island in the Apostle Islands National Lakeshore (APIS) of Lake Superior reveal that tree cover has increased on the island since the 1930s. This observation led to questions about fire, vegetation, and climate history of the area and highlighted the need for historical information to inform fire management and conservation efforts. To provide this information, we developed paleoenvironmental records of fire, vegetation, and surface-moisture conditions from peat and sediment cores collected from two sites on the island, and we used these records along with previously collected data to provide a long-term perspective on fire, vegetation and island development, and hydrologic changes spanning approximately the past 5,000 years. The primary objective of this study was to provide APIS resource managers with information on fire frequency for the past several thousand years, as well as information on fire-vegetation and fire-climate relationships, so that this long-term perspective could inform fire management decisions. Pine-dominated vegetation on Stockton Island is restricted to a tombolo, a sandy geomorphological feature that connects two former islands. Sediment and peat cores were collected from two sites on the tombolo: Stockton Bog and Stockton Lagoon. Standard methods were used for pollen analysis and the reconstruction of bog surface-moisture using testate amoebae, a group of moisture-sensitive protists that produce decay-resistant shells. Macroscopic and microscopic charcoal concentrations and accumulation rates were estimated and used to identify particularly large peaks in charcoal (fire episodes) using established methods. Fire frequency was expressed as the number of fire episodes per 500 years and summarized with a 500-year moving window to assess changes over time.

Fire, vegetation, and water-level history from the Stockton Island tombolo: Apostle Islands National Lakeshore

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