Remnants of virgin hemlock Tsuga canadensis (L.) Carr. forest in the Porcupine Mountains, Michigan, USA, have experienced inadequate hemlock regeneration lasting several decades. White-tailed deer Odocoileus virginianus Zimmermann browsing seems to be the major cause of the observed decline of hemlock regeneration, rather than poor seedbed conditions or changing climate. In some areas, significant changes in the size-structure of the forest have already occurred, with a shift of dominance from hemlock to sugar maple Acer saccharum Marsh. taking place. A simulation of forest development is used to predict the changes in forest structure that will occur if no action is taken to control browsing. From this simulation it is estimated that in less than 150 years, hemlock will become only a minor component of the forest over large areas where it is currently the major dominant.
Bibliographical noteFunding Information:
The cooperation of Robert Vanderwall and the staff of the Porcupine Mountains Wilderness State Park in relation to the field work for this project is gratefully acknowledged. We also thank Elsworth Harger and G. R. Stephens for access to permanent plot data. Research supported by the School of Natural Resources, College of Agricultural and Life Sciences, University of Wisconsin-Madison and by the Mclntire-Stennis Cooperative Forestry Research Program.
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