80 THE MICHIGAN BOTANIST Vol. 52 GROUND VEGETATION OF OLD-GROWTH WHITE PINE STANDS AT THE HURON MOUNTAIN CLUB RESERVE AND ESTIVANT PINES IN UPPER MICHIGAN Dennis A. Riege University of Maryland University College 17 Longmeadow Avenue Middletown, RI 02842 [email protected] ABSTRACT 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 plots in the Huron Mountain Club Reserve in - cluded a Pinus strobus –Tsuga canadensis –northern 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 × 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 indicated wet-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 have suppressed other species. The vegetation at both sites indicated that deer herbivory was relatively light in comparison to other re - gional studies. Future studies in these long-term permanent plots will investigate intrinsic late-suc - cessional dynamics of these forests, as well as the effects of extrinsic forces, such as herbivory. KEYWORDS : Pinus strobus , Huron Mountains, Estivant Pines, species richness, ground vege - tation INTRODUCTION Long-term permanent plot studies are needed to test theoretical patterns of succession and to suggest hypotheses on vegetation dynamics (Bakker et al . 1996; Johnson and Miyanshi 2008 ). Permanent plots that monitor understory changes in late-successional forests are especially rare. Vegetation dynamics of ground communities are poorly understood, especially in old-growth forests (Woods et al. 2012). Rooney et al. (2004) and Wiegmann and Waller (2006) ob - served that species composition of upland forest understories in the Upper Mid - west have changed substantially in 50 years, with a decrease in native species di - versity and an increase in exotic species. Maintaining biodiversity is a goal of forest managers (Barbier et al. 2008; Woods et al. 2012). Barbier et al. (2008) concluded that “future research is needed to gain a better understanding of the 2013 THE MICHIGAN BOTANIST 81 FIGURE 1. Location of Huron Mountain Club Reserve and Estivant Pines in Upper Michigan. relationship between overstory and understory diversity.” Wiegmann and Waller (2006) believed that “quantitative, long-term, retrospective studies are essential if we are to detect and respond to ecological change.” Herbivory by abundant white-tailed deer ( Odecoileus virginianus ) is a major regional influence in both herb composition of the forest floor (Cote et al. 2004; Kraft et al. 2004; Wieg - mann and Waller 2006) and regeneration success of tree seedlings (Rooney et al. 2002; Rooney and Waller 2003; Witt and Webster 2012). In an area of low deer densities, Woods et al. (2012) suggested changing canopy composition and un - derstory competition as possible causes of an observed decline in fine-scale di - versity in the forest floor of late-successional stands . As part of a long-term study of Pinus strobus stands in Upper Michigan and northern Wisconsin (Riege 2011, 2012), I established large permanent plots in Michigan’s Huron Mountain Club Reserve and Estivant Pines (Figure 1) . These stands will be undergoing transition in future decades , since most of the P. strobus trees are large canopy emergents , and very few are saplings or seedlings . The plots will be utilized to investigate topics of current regional concern, such as effects on vegetation of deer herbivory, exotic species invasions, and climate change, as well as general successional dynamics . Most ground vegetation stud - ies concentrate on herbs and shrubs , but exclude seedlings of tree species from the community analysis (but see Schiller and Mladenoff 2002, Frelich et al. 2003 ). However, since tree seedlings are an important part of the competitive array on the forest floor, they are included in the analysis presented here . In ad - dition, tree seedlings are emphasized because differential regeneration and growth of tree species will ultimately determine the long-term composition of the forest. This investigation of the ground vegetation of the permanent plots is a com - panion paper to that of Riege (2011) on tree and sapling demography of the two forests. This article (1) examines community composition of the forest floor 82 THE MICHIGAN BOTANIST Vol. 52 among these old-growth stands, particularly in relation to the overstory , and (2) presents reference data for future studies of vegetation dynamics of these forests. MATERIALS AND METHODS Study Areas The Huron Mountain Club has maintained a 2500 ha reserve for over a century in Michigan’s Huron Mountains that border Lake Superior (Figure 1). The reserve contains extensive forests of old- growth mesic Tsuga canadensis , Acer saccharum , and northern hardwoods, which have been the subject of several previous studies (Braun 1950; Woods 2000 ; Woods 2008; Marx and Walters 2008). Old-growth Pinus strobus stands are uncommon in the mesic forests of the Huron Mountains, though emergent pines are a component of many T. canadensis –northern hardwoods stands there . During 2007 and 2008 , I established two adjacent permanent plots totaling 2.4 ha by Fisher Creek in the Huron Mountain Club Reserve, located within 46 o51.4 ′–51.6 ′ N and 87 °52.9 ′–53.1 ′W. The north plot (FCN = Fisher Creek North) covered 1.58 ha of P. strobus –T. canadensis –northern hardwoods forest (Table 1) . The adjacent 0.82-ha south plot (FCS = Fisher Creek South ) contained an atypical P. strobus –Picea glauca –Acer rubrum stand with a thick sapling understory of A. saccharum (Figure 2) that has been described by Thompson (1985) , Simpson et al. (1990), and Riege (2011) . Fahey (2011) reported that the oldest white pine among core samples at the Fisher Creek stands was about 210 years old . Plot ma ps are on file in reports to the Huron Mountain Wildlife Foundation (www.hmwf.org). Schwenner (2007) classified most of the soils in the FCS plot as belonging to the Evart-Pelkie-Sturgeon complex of deep, poorly drained, permeable soils that form in silty and sandy alluvium , and most of those in the FCN plot as belonging to the Kalkaska-Waiska complex of deep, well-drained, permeable soils on sandy outwash. Estivant Pines, which contains the largest preserved tract of old-growth Pinus strobus in Michi - gan, is located in a 206 ha sanctuary of the Michigan Nature Association, south of Copper Harbor near the tip of the Keweenaw Peninsula (Figure 1) . During 2010, I established a 0.78-ha permanent plot (EPU = Estivant Pines Upland ) in an upland P. strobus stand known as Cathedral Grove (Figure 3) that followed the top of a broad ridge. A second 0.75 ha plot (EPG = Estivant Pines Gap ) was es - tablished to the west on a lower plateau, separated from the EPU plot by a 20 –30 m wide ravine . The EPG plot contained large gaps (0.03-0.06 ha) and a diversity of tree regeneration . Below the emer - gent pines at Estivant Pines , Acer saccharum and Abies balsamea were dominant (Table 1) . The old - est P. strobus sampled in the plots by Fahey (2011) was about 260 years old . The Estivant Pines plots were located within 47 °26.2 ′–26.4 ′ N and 87°52.8 ′–53.1 ′ W. Maps of the Estivant Pines plots are on TABLE 1. Basal area, in m 2/ha, of tree species at the study plots at Huron Mountains (FCN and FCS) in 2011 and at Estivant Pines (EPU and EPG) in 2010. The acronyms of the study plots are defined in the text. FCN FCS EPU EPG Pinus strobus 14.4 29.2 25.0 5.5 Tsuga canadensis 12.8 0.9 Acer saccharum 15.4 1.3 12.5 10.7 Acer rubrum 1.9 5.1 2.6 4.1 Quercus rubra 0.2 1.6 Betula alleghaniensis 6.1 0.6 1.9 2.4 Betula papyrifera 0.2 0.3 0.2 Picea glauca 0.9 5.6 0.4 0.5 Abies balsamea 0.6 0.4 8.2 6.1 Thuja occidentalis 0.9 3.3 2.9 Tilia americana 0.1 Ostrya virginiana 0.2 0.0 0.0 0.3 Acer pensylvanicum 0.0 0.0 Totals 53.4 43.1 54.6 34.7 2013 THE MICHIGAN BOTANIST 83 FIGURE 2. Photograph of Acer saccharum sapling thicket in the FCS plot at Huron Mountain Club Reserve. file in reports to the Michigan Nature Association (www.michigannature.org). Soils at both plots were classified by Tardy (2006) as Arcadian-Dishno-rock outcrop complex of well-drained, cobbly and very gravelly fine sandy loams. All living stems greater than or equal to 5 cm DBH were measured in the Huron Mountain plots in 2011 and in the Estivant Pines plots in 2010 , the same years that the ground transect studies de - scribed below were undertaken.