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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@example.com
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
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
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FIGURE1.LocationofHuronMountainClubReserveandEstivantPinesinUpperMichigan. 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
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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
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 46o51.4.–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 maps 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 m2/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
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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. Tree species dominance from these measurements is summarized in Table 1. In the same years, densities of small sapling (individuals of 1.0-4.9 cm diameter DBH) were determined by counting all saplings within 2 m of the midline of the transects (Table 2).
The presence by species of tree seedlings (defined for purposes of this study as individuals whose stems at DBH are less than 1 cm in diameter), shrubs, and herbs was recorded on August 1-3, 2010 at Estivant Pines and on June 21–24, 2011 at the Huron Mountain Club along marked transect lines that run across the plots, in continuous strips of 2 . 2 m quadrats. The percentage cover of the species was not estimated, but presence/absence data were tallied. This transect method was chosen to facil- itate the measurement over time of the spread or contraction of ground species, as well as for effi- ciency in periodic monitoring of the permanent plots. The total number of quadrats was 326 in the FCN plot, 145 in the FCS plot, 156 in the EPU plot, and 196 in the EPG plot. Transect lines were spread out to cover all sections of the plots. Some transect locations in the FCN and EPG plots were chosen to pass through canopy gaps to monitor long-term changes within the gaps.
During subsequent field trips to the plots in 2012 and 2013, species that were difficult to identify in the quadrats were reexamined. Voucher specimens of these species were collected and deposited in the Northern Michigan University Herbarium (NM), where they were subsequently identified. In- dividuals of Carex could not always be identified to species in the field, hence are listed as “Carex spp.“ in Table 3. However, it was evident when more than one Carex species was present in a
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FIGURE 3. Photograph of the EPU plot at Estivant Pines with large Pinus strobus, intermediate hardwoods, and Thuja occidentalis–Abies balsamea understory.
quadrat. Thus, for species richness data, the number of Carex species in each quadrat was recorded. Carex specimens submitted to NM from the Huron Mountain Club Reserve were identified as C. gracillima, C. pedunculata, and C. arctata and from Estivant Pines as C. gracillima and C. commu- nis. In each of the plots other than EPU, there was one unidentified grass species in one of the quadrats.
For purposes of this study, the term “quadrat species richness” means the number of species found in a given quadrat. To determine if the mean quadrat species richness differed among the four
TABLE 2. Number of small saplings of each species per ha, based on transect samples, in 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 128 Acer saccharum 169 1603 40 51 Acer rubrum 60 112 83 Quercus rubra 88 191 Betula alleghaniensis 48 153 Picea glauca 31 32 6 Abies balsamea 753 1595 Thuja occidentalis 577 198 Ostrya virginiana 180 8 32 Acer pensylvanicum 26 26 Totals 406 1689 1130 2437
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plots, quadrat species richness values in the plots were compared by the Bonferroni method after one-way ANOVA, with Statistix 9.0. software. Nomenclature follows Voss and Reznicek (2012) for seed plants and Reznicek, Voss, and Walters (2011) for ferns and fern allies. This paper lists only those species that were found in the quadrats during the sampling times. Thus, it does not constitute a complete flora of the stands. Wells and Thompson (1976) published a flora of the Huron Moun- tains, but a flora of Estivant Pines is not available.
Table 3 lists 57 ground cover species encountered in the quadrats. The only nonnative species was Veronica officinalis, which was present in small amounts at Estivant Pines. In the Huron Mountains, quadrat species richness was signifi- cantly greater in the FCN plot than in the FCS plot (Table 4). This was due to the greater frequency and diversity of tree seedlings in the FCN plot (Table 3); when tree seedlings are excluded, richness does not differ in the FCN and FCS plots. Ostrya virginiana and Acer pensylvanicum seedlings were much more common in the FCN plot than in the FCS plot. Acer saccharum seedlings were the most frequent species in the FCN plot. Streptopus lanceolatus, Maianthemum canadense, and Trientalis borealis were the most common herbs (Table 3). Dry- opteris carthusiana was the most common species in the FCS plot, where A. sac- charum, M. canadense, and T. borealis also occurred in the majority of quadrats. Among the major differences between the two Huron Mountains plots was the much greater presence of Streptopus lanceolatus and the lycopods Dendroly- copodium dendroides and Huperzia lucidula in FCN. In contrast, the FCS plot contained more individuals of Osmorhiza claytonii, Viola blanda, and V. cucul- lata.
The Estivant Pines plots were considerably less rich in species than were the Huron Mountain plots (Table 4). Among the former, the EPG plot was greater in quadrat species richness than the EPU plot, which might be attributed to the presence of canopy gaps in the EPG plot. Tree seedlings contributed the major component of the species richness in both of the Estivant Pines plots, which con- trasted with tree seedlings comprising less than one-third the richness in the Huron Mountains plots. In the EPU plot, ground cover was dominated by Thuja occidentalis seedlings and was strikingly depauperate in species of herbs (Tables 3 and 4). Maianthemum canadense was the most common herb in the EPU plot, but occurred in only 21% of the quadrats (Table 3). Most tree species were more common in EPG than in EPU. Graminoid species were more abundant in EPG, as were the shrubs Corylus cornuta and Rubus parviflorus (Table 3).
To investigate the dominant role that seedlings of Thuja occidentalis seemed to play in the ground vegetation of Estivant Pines, the species richness of the quadrats in which T. occidentalis was present was compared with the quadrats in which it was absent. Quadrats in which T. occidentalis was present had signifi- cantly (p < 0.05, t-test) fewer species (2.8 ± 0.1 SE) than those without (3.3 ± 0.2 SE).
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TABLE 3. Frequencies of ground species in the study plots, as measured by the percentage of quadrats in which that species is present. The acronyms of the study plots are defined in the text.
FCN FCS EPU EPG Tree Seedlings Abies balsamea L. 2.5 2.1 14.1 32.7 Acer pensylvanicum L. 27.0 13.1 Acer rubrum L. 23.3 22.1 25.0 23.0 Acer saccharum Marshall 87.7 77.2 20.5 55.6 Acer spicatum Lam. 1.3 1.1 Betula alleghaniensis Britton 0.7 0.6 3.1 Ostrya virginiana (Mill.) K. Koch 24.5 7.6 5.1 Picea glauca (Moench) Voss 3.1 2.8 3.2 9.2 Pinus strobus L. 1.5 2.1 1.3 11.7 Quercus rubra L. 1.2 16.0 30.1 Thuja occidentalis L. 70.5 33.7 Tilia americana L. 0.6 Tsuga canadensis L. 3.4 2.1 Other Species Anemone quinquefolia L. 3.4 Aralia nudicaulis L. 14.7 22.1 7.7 2.0 Athyrium felix-femina L. 1.2 0.7 Carex spp 34.4 31.0 2.6 17.9 Chimaphila umbellata L. 5.8 4.1 Cinna latifolia (Goepp.) Griseb. 0.6 13.8 Clintonia borealis (Aiton) Raf 11.3 4.8 1.9 Coptis trifolia (L.) Salisb. 2.5 3.4 Cornus canadensis L. 0.3 4.1 Cornus rugosa Lam. 1.0 Corylus cornuta Marshall 2.5 2.8 10.3 28.1 Dendrolycopodium dendroides (Michx.) A. Haines 35.3 Dryopteris carthusiana (Vill.) H.P.Fuchs 46.6 93.6 5.6 0.6 Equisetum sylvaticum L. 0.7 Eurybia macrophylla (L.) Cass 7.1 1.4 Galium triflorum Michx. 0.6 4.1 Gaylussacia baccata (Wangenh.) K. Koch 1.0 Goodyera oblongifolia Raf. 0.3 4.5 5.6 Gymnocarpium dryopteris (L.) Newm. 0.9 Hepatica americana (DC) Ker Gawl. 2.5 0.6 0.5 Huperzia lucidula (Michx.) R. Trevis 13.8 2.8 Impatiens pallida Nutt. 0.6 Linnaea borealis L. 0.3 Lonicera canadensis Marshall 20.9 9.7 6.4 10.7 Maianthemum canadense Desf. 54.9 79.3 21.2 17.3 Mitchella repens L. 8.6 6.1 Onoclea sensibilis L. 1.4 Oryzopsis asperifolia Michx. 22.1 5.5 15.3 Osmorhiza claytonii (Michx.) C.B.Clarke 7.4 21.4 Polygonatum pubescens (Willd.) Pursh 1.2 Pteridium aquilinum (L.) Kuhn 8.3 2.8 4.1 1.9 Pyrola elliptica Nutt. 3.1 0.7 Ribes lacustre (Pers.) Poir. 0.7 0.5 Rubus parviflorus Nutt. 1.2 3.4 4.5 26.5 Sambucus racemosa L. 0.7 Scutellaria lateriflora L. 0.6
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TABLE 3. Continued.
FCN FCS EPU EPG
Sorbus americana Marshall 1.9 1.5 Streptopus lanceolatus (Aiton) Reveal 56.4 6.9 Trientalis borealis Raf. 50.6 52.4 1.0 12.8 Trillium cernuum L. 2.8 unidentified grass species 0.3 0.7 0.5 Veronica officinalis L. 1.9 2.6 Viola blanda Willd. 3.7 24.8 Viola cucullata Aiton 5.5 Viola pubescens Aiton 3.4
The ground species composition of the Huron Mountains plots was typical of regional Tsuga canadensis–Acer saccharum forests (Curtis 1959; Willis and Coffman 1975; Woods et al. 2012). The tree composition of the FCN plot (Table 1) fits descriptions of a “classic” Tsuga canadensis–Pinus strobus–northern hardwoods forest (Nichols 1935; Braun 1950; Curtis 1959). A Pinus strobus–Picea glauca–Acer rubrum stand, as found in the FCS plot, has not gen- erally been recognized as a common forest association (Eyre 1980; Wendel and Smith 1990). Although the FCS plot contained a flora similar to that of the FCN plot, the differences in the ground community indicated that the FCS plot was slightly moister or more wet-mesic than the mesic FCN plot when compared to regional community classifications (Curtis 1959; Willis and Coffman 1975; Kotar et al. 2002), as determined by the greater abundance in the FCS plot of species such as Osmorhiza claytonii, Viola blanda, V. cucullata, and Dryopteris carthusiana. (Table 3). Classification as a wet-mesic stand, however, is some- what counter to the dominance in the FCS plot by Pinus strobus, which is more often associated with dry-mesic sites (Curtis 1959; Wendel and Smith 1990). Pinus strobus is also known, however, to occupy wetter sites with poor drainage and less competition (Abrams 2001). The FCS plot lay slightly lower in eleva-
TABLE 4. Species richness of ground plants in each study plot, as measured by the mean number of species per quadrat ± standard error. Column a is calculated by including all species present in all quadrats. Column b is calculated by including all species except tree seedlings in all quadrats. Dif- ferent superscript letters within each column indicate that the mean number of species per quadrat differs by p < 0.01 by Bonferroni comparison after one-way ANOVA.
Species Richness (a) (b) Plot Tree seedlings included Tree seedlings excluded FCN 6.0 ± 0.1 a 4.1 ± 0.1 a FCS 5.3 ± 0.2 b 3.9 ± 0.1 a EPU 2.3 ± 0.2 c 0.7 ± 0.1 b EPG 3.7 ± 0.1 d 1.6 ± 0.1 c
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tion than the FCN plot and is adjacent to Fisher Creek, which is consistent with its more wet-mesic nature. During the autumn of 2011, after the June 2011 sur- vey of ground vegetation reported in this paper was carried out, I noticed that beaver had started to cut saplings in the FCS plot that caused flooding at the edges of the plot. Perhaps past flooding episodes have influenced the evolution of vegetation in the FCS plot.
The Pinus strobus–northern hardwoods forest at Estivant Pines differed from the Huron Mountains stands by the absence of Tsuga canadensis and the pres- ence of a dense Abies balsamea–Thuja occidentalis subcanopy (Tables 1 and 2). The Estivant Pines plots have an essentially three-layered canopy in which Pinus strobus is emergent, Acer saccharum dominates the middle layer, and Abies bal- samea and Thuja occidentalis are dominant below (Figure 3). The ground cover at Estivant Pines was considerably more barren and less diverse than at the Huron Mountains stand (Tables 3 and 4). Community composition at Estivant Pines indicated a dry-mesic site, with occupation by species such as Quercus rubra, Chimaphila umbellata, Goodyera oblongifolia, and P. strobus (Curtis 1959; Maycock 1961; Chadde 2013). A dry-mesic classification is appropriate for the well-drained, sandy loam soils. The most frequent ground-cover species, Thuja occidentalis, is usually associated with wet-mesic or wet stands in the re- gion (Maycock and Curtis 1960; Johnston 1990), but is also known to have a bi- modal distribution in both wet and dry sites (Hofmeyer et al. 2009). Thickets of Abies balsamea saplings and, to a lesser extent, Thuja occidentalis, dominated the subcanopy of much of the Estivant Pine plots (Table 2). Maycock (1961) re- ported that boreal stands of Abies balsamea–Picea glauca become more com- mon at the northern tip of the Keweenaw Peninsula, as presumably do boreal components of mixed stands. He also found that Acer saccharum was common in Keweenaw boreal stands and tended to increase in importance over time. Maycock reported Thuja occidentalis to be a common associate in these forests, especially in wet-mesic stands. Dense stands of T. occidentalis have been re- ported to inhibit colonization by other species (de Blois and Bouchard 1995). At Estivant Pines, species richness declined in quadrats where T. occidentalis seedlings were present in the ground cover. T. occidentalis can persist for many decades in the form of suppressed understory plants that spread by vegetative re- production (Johnston 1990; Hofmeyer et al. 2009). Thuja occidentalis has been shown to produce allelopathic compounds that inhibit herb germination (Oster et al. 1990).
Ground species richness has been reported to decrease as dominance by Tsuga canadensis in a forest increases (Auclair and Goff 1971, Barbier et al. 2008, Ellum et al. 2010). In contrast to this trend, ground species richness was highest in the FCN plot (Table 4), the plot in which T. canadensis is a major component (Table 1). In the Dukes Research Area in Marquette County, Michi- gan, Woods et al. (2012) also found species richness to be higher in Tsuga-dom- inated forests than in other upland forests. The mean species per quadrat values at the Huron Mountains plots were similar to those reported in mature Upper Michigan Tsuga canadensis–Acer saccharum forests by Scheller and Mladenoff (2002), who used 2 m . 2 m quadrats and included tree seedlings, as in this study. However, the low species richness at Estivant Pines contrasted with May-
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cock’s (1961) finding that the herb layer of the Keweenaw Peninsula bo- real–maple forests was relatively species diverse. Barbier et al. (2008) noted that herb diversity can be depressed by a developed subcanopy, as in the Abies bal- samea–Thuja occidentalis thickets in the Estivant Pines plots.
Rooney et al. (2004) and Wiegmann and Waller (2006) reported changes in the understory vegetation of 62 upland forest stands in northern Wisconsin and Upper Michigan that had been sampled more than 50 years previously by Curtis (1959) and his students. Wiegmann and Waller (2006) identified 21 “winner” species that significantly increased in frequency and 21 “losers” that decreased. An increase in density of exotic species was also discovered. They concluded that tolerance to deer herbivory was a key factor in determining the winner species and that deer herbivory also influenced the decline in the ratio of native to nonnative species. Species in the Huron Mountains and Estivant Pines plots included 13 of the Wiegmann and Waller loser species and 10 of the winners. The abundance of the grazer-prone loser species, such as Streptopus lanceolatus, Aralia nudicaulis, and Clintonia borealis, may indicate that deer herbivory is relatively low in the Huron Mountains stands. Deer densities in 2009 in the Upper Peninsula were mapped by the Michigan DNR (2010) to be lowest in areas near Lake Superior and higher near the Wisconsin border. Thuja occiden- talis is heavily browsed in the region, where deer have inhibited its regeneration in many stands (Rooney et al. 2002). The abundance of T. occidentalis was in- dicative of low browsing pressure at Estivant Pines. On the other hand in the Huron Mountains plots, Riege (unpublished data) recorded sufficient browsing on Tsuga canadensis seedlings to suggest that it was a major factor in the ab- sence of T. canadensis in the small sapling cohort. Regeneration of T. canaden- sis suffers greatly from browsing in the region (Anderson and Loucks 1979; Rooney and Waller 2003; Witt and Webster 2010). As noted earlier, only one ex- otic species was recorded in the quadrats—Veronica officinalis at Estivant Pines. Both the Huron Mountains and the Estivant Pines study sites are located deep within forest preserves, though a well-traveled hiking trail crosses the Estivant Pines plots.
The fate of tree seedlings will determine the future of the forest in the long run. In the transect samples at the Huron Mountains stand, only five species of small saplings were found, although 11 species were present as seedlings (Tables 2 and 3). Along with herbivory (as seen in Tsuga canadensis), shading may have been a factor in this reduction. The Tsuga canadensis–Acer saccharum cover in the FCN plot and the A. saccharum sapling thicket in the FCS plot likely inhib- ited shade-intolerant seedlings. In contrast to the Huron Mountains plots, most of the species present in the Estivant Pines plots as seedlings were also represented as small saplings (Tables 2 and 3). Canopy gaps were a likely factor in survival at the EPG plot. Interestingly, the dense subcanopies of Abies and Thuja at Esti- vant Pines did not exclude the other species from reaching the sapling stage. Acer saccharum seedlings were ubiquitous in the Huron Mountains plots and abundant in the EPG plot (Table 3). Adventitious A. saccharum seedlings may survive years in a suppressed state (Woods 2008). In contrast, at the EPU plot, A. saccharum seedlings were present in only one-fifth of the quadrats, even though
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A. saccharum trees were common throughout the plot. Perhaps regeneration of A. saccharum was deterred by the cover of Thuja occidentalis. Although old-growth Pinus strobus trees were abundant in these stands, P. strobus seedlings were rare at both sites, and saplings appeared only in the tran- sects at the EPG plot (Tables 2 and 3). This probably reflected its intolerance to dense shade (Wendel and Smith 1990). Very slow growth of P. strobus seedlings, with episodes of browse back, have been noted over a 5-year study in the Huron Mountains and Estivant Pines plots (Riege, unpublished data). With the possible exception of the EPG plot, the outlook for long-term reproduction of P. strobus in the forests is dim. However, the findings of Riege (2012) caution against using present demography to project into the future. He found recent surges in P. strobus reproduction in Wisconsin forests that were not indicated by demo- graphic studies that were reported decades earlier in these forests.
The most important results of this project on dynamics of old-growth forests will be in the future. Long-term studies of the ground vegetation will permit the investigation of general late-successional dynamics. For example, will fine-scale species richness of ground plants in undisturbed forests decrease over time, as Woods et al. (2012) reported in an Upper Michigan late-successional stand? The Huron Mountains and Estivant Pines plots also provide an opportunity to address specific topics, such as effects of beaver cutting on ground vegetation of the FCS plot. Deer browsing effects will be examined in FCN as the control plot for a nearby 2 ha exclosure. Potential suppression of ground cover by Thuja occiden- talis will be followed at the EPU plot. Future effects of invasive species or cli- mate change on the forest floor can be examined. Results on survival and growth of white pine seedlings within the ground communities will be synthesized with those of sapling and canopy stages to provide insights to managers who wish to maintain or restore white pine in regional forests. The fate of forests is unpre- dictable from present composition (Bakker et al. 1996; Riege 2012).
The Huron Mountain Wildlife Foundation has generously supported research at the Huron Moun- tain Club Reserve. I especially thank their director Kerry Woods for advice when initiating and while continuing my regional studies. The Hanes Trust and the Michigan Botanical Foundation made pos- sible the Estivant Pines study. Thanks are due to Michael Rotter at the Northern Michigan University Herbarium, who assisted in the identification and deposit of voucher specimens, and to Katie Frerker, Sarah Johnson, and Don Waller, who helped in the identification of plants at the Huron Mountain Club Reserve.
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