Department of Ecology, Evolution, and Behavior
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Browsing Department of Ecology, Evolution, and Behavior by Author "Calcote, Randy R."
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Item 3000 years of abundant hemlock in upper Michigan(1995) Davis, Margaret B.; Sugita, Shinya; Calcote, Randy R.; Parshall, Timothy E.; Ferrari, James B.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.Item Patch formation and maintenance in an old-growth hemlock-hardwood forest(1993) Frelich, Lee E.; Calcote, Randy R.; Davis, Margaret B.; Pastor, JohnCause of patch formation was investigated on a 7.2 ha study area in Sylvania Wilderness Area, a primary forest remnant in Upper Michigan comprising a mosaic of hemlock, sugar maple, and mixed-forest patches. Spatial autocorrelation analysis of the stem map indicated that, although most species pairs have a neutral association between canopy trees and understory trees of other species, hemlock and sugar maple canopy trees both have strong positive self association and negative reciprocal association with each other. No species pairs have a positive reciprocal association on regeneration with each other. MOSAIC, a Markov simulation model in which transition probabilities depend on neighborhood species composition, shows that the negative reciprocal association between hemlock and sugar maple of the intensity observed in this study, could lead to spatial separation into monodominant patches over long time periods (3000 yr). The mixed-forest patches are along spatial continua of varying steepness between sugar maple and hemlock patches. Interactions sugar maple and hemlock overstory and understory trees, along with the pattern of invasion of hemlock, provide a reasonable explanation for the patch structure. Pedological, topographical, and disturbance history differences do not coincide with the location of patches within upland forests on the study area.Item Patchy invasion and the origin of a hemlock-hardwoods forest mosaic(1998) Davis, Margaret B.; Calcote, Randy R.; Sugita, Shinya; Takahara, HikaruThe record of forest invasion by castern hemlock (Tsuga canadensis) during the course of Holocene migration provides useful information about invasion processes in temperate forest, a system that has been invaded by few exotic species. We used fossil pollen preserved in small forest hollows, which record forest composition on the scale of 1-3 ha, to study hemlock invasion of forests in the Sylvania Wilderness in the upper peninsula of Michigan, where there is now a mosaic of 3-30 ha stands dominated either by hemlock or by sugar maple (Acer saccharum) and basswood (Tilia americana). Fossil pollen was interpreted by comparison with 66 surface samples from small hollows in Michigan and Wisconsin, using three different statistical methods: pollen ratios, a dissimilarity index, and canonical variates analysis (CVA) ordination. We found that four hemlock stands along a 10-km transect across Sylvania originated as patches of white pine (Pinus strobus) forest that were invaded by hemlock ∼ 3000 yr ago (calibrated 14C dating) when hemlock expanded its range in northern Michigan. Invasion occurred at about the same time (within 800 yr) at all sites but was not associated with disturbance at any site. Over the next several thousand years hemlock coexisted with white pine, but eventually, at a time that differs from site to site, hemlock became dominant, and white pine disappeared from all but one of the four stands. These changes were apparently driven by climate changes over the last 4000 yr that caused the water table to rise (Brugam and Johnson 1997). The history of four nearby maple stands is more variable and less well understood. Unlike the hemlock stands, three of the four maple patches were not dominated by pine at the time of hemlock invasion, but instead had abundant oak (Quercus) and/or maple. Two of these stands were not invaded by hemlock, and the third, if invaded at all, was invaded for a few centuries by low densities of hemlock trees. Thus invasion by hemlock was sensitive to the species composition of the resident forest. Sugar maple and basswood increased in these stands, and by 2000 to 800 yr ago, depending on site, they resembled modern maple stands. The fourth patch was invaded by hemlock, but it was converted to a maple stand 1000-500 yr ago. A wood layer in the sediment is evidence that a catastrophic windstorm may have been responsible.