Hemlock invaded the Great Lakes Region about 5500 years ago, colonizing lower Michigan and the Upper Peninsula as far west as Iron River. Over the past 3000 years it has become much more abundant in the eastern Upper Peninsula and has extended its range slowly westward and southward into Wisconsin. In the Sylvania Wilderness in Gogebic County, Upper Michigan, fine-scale paleoecological studies record hemlock's invasion of individual forest stands about 3000 C-14 years ago. Hemlock invasion was patchy as it became established in forests previously dominated by white pine, red maple, and oak. Pollen records from modern hemlock stands show that hemlock increased within a few centuries to become an abundant species, but white pine remained co-dominant for 1000-1500 years. Pollen records from two hardwood stands now dominated by sugar maple and basswood show that hemlock has never become abundant in these stands. Pollen evidence from mixed stands and from the edges of hemlock stands indicate marked fluctuations in the ratio of hemlock to sugar maple, with sugar maple abundance responding positively to disturbance by fire or by wind. Following clearcutting 50-60 years ago both hemlock stands and hardwood stands in western Upper Michigan have been succeeded by hardwoods, and the mosaic of hemlock and hardwood patches is no longer visible. We conclude that in the absence of disturbance hemlock stands can persist for many centuries, including the Medieval warm period (900-1300 AD) when the climate was as warm as today, and the Little Ice Age (1450-1850 AD) when the climate was colder. Although hemlock seedlings are not abundant in hemlock stands today, there are enough hemlock trees in the understory to assure continued canopy recruitment for several centuries.
Davis, Margaret B., et al. "3000 Years of Abundant Hemlock in Upper Michigan". Hemlock Ecology and Management: Proceedings of a Regional Conference on Ecology and Management of Eastern Hemlock, September 27-28, 1995. Iron Mountain, MI.
Davis, Margaret B.; Sugita, Shinya; Calcote, Randy R.; Parshall, Timothy E.; Ferrari, James B..
3000 years of abundant hemlock in upper Michigan.
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