GROUND VEGETATION OF OLD-GROWTH WHITE PINE STANDS AT THE HURON MOUNTAIN CLUB RESERVE AND ESTIVANT PINES IN UPPER MICHIGAN

摘要

Because understory dynamics of late-successional forests are little understood, examination of the composition and change of ground vegetation was included in long-term permanent plot studies of two preserved forests in Upper Michigan. Adjacent plotsin the Huron Mountain Club Reserve included a Pinus strobus-Tsuga canadensis-norihtm hardwoods forest and an atypical Pinus strobus-Picea glauca stand with dense undergrowth of Acer saccharum saplings. At Estivant Pines one plot contained a stand of Pinus strobus-Acer saccharum-Abies balsamea, and the second plot held a similar stand with large gaps. The presence of all species of vascular plants on the forest floor was recorded in transects of continuous 2 x 2 m quadrats across the plots. Species in the Huron Mountain Club Reserve plots were typical of old-growth upland conifer-northern hardwoods stands, in which Acer saccharum seedlings, Maianthemum canadense, and Dryopteris carthusiana were the most common components. Community composition indicatedwet-mesic conditions at one of the plots and mesic conditions at the other. Understory species richness was greatest in the plot in which Tsuga canadensis is a co-dominant, a result opposite that of most previous studies. Species richness was less in the dry-mesic Estivant Pines plots, in which tree seedlings constituted the bulk of the richness, than in the Huron Mountains plots. Ground vegetation in the plot at Estivant Pines without gaps was dominated by Thuja occidentalis seedlings, which may havesuppressed other species. The vegetation at both sites indicated that deer herbivory was relatively light in comparison to other regional studies. Future studies in these long-term permanent plots will investigate intrinsic late-successional dynamics ofthese forests, as well as the effects of extrinsic forces, such as herbivory.