2002 THE MICHIGAN BOTANIST 5 BRYOPHYTES ASSOCIATED WITH HART’S TONGUE FERN (ASPLENIUM SCOLOPENDRIUM VAR. AMERICANUM) ON DOLOMITE ROCKS IN MACKINAC COUNTY, MICHIGAN Janice M. Glime Department of Biological Sciences Michigan Technological University Houghton, MI 49931 [email protected] ABSTRACT Nineteen bryophyte taxa were found within the circle of influence of the hart’s tongue fern. These formed zonation patterns on individual rocks, with pleurocarpous mosses such as Thuidium recognitum, Anomodon attenuatus, Brachythecium spp., and Plagiomnium affine predominating. One- and two-year-old fern sporophytes were found in disturbed patches where the thick moss mats were missing and only a thin layer of young mosses, fern and moss rhizoids, and detritus covered the rock. Older sporophytes occurred predominantly on the sides of rocks where they were supported by thick mats of mosses. INTRODUCTION Asplenium scolopendrium Linnaeus var. americanum (Fernald) Kartesz & Gandhi is federally listed as threatened in the United States, with over 90% of the individuals occurring in only two counties of central New York (Cinquemani Kuehn & Leopold 1992). Known also as Phyllitis scolopendrium (Linnaeus) Newman var. americanum Fernald, the hart’s tongue fern, it grows in small pop- ulations on dolomite rocks of the Engadine series in Mackinac County, Michi- gan, where it is protected by U. S. Forest Service ownership. The dolomite series has both Mg and Ca, providing an essential blend of nutrients that permit plants to grow (U.S. Fish and Wildlife Service, Division of Endangered Species, 1990), whereas many other kinds of limestone rocks are lacking in some essential nu- trient. The hart’s tongue-bearing rocks of this series are covered with bryophytes, whereas in New York Cinquemani Kuehn and Leopold (1993) found that the ma- ture plants more typically were on bryophyte-poor rocks. Because little is known about the ecology of the Michigan hart’s tongue populations, it is desirable to understand their association with these bryophytes. It is possible that the bryophytes provide some necessary aspect to the microhabitat of these endan- gered ferns. And because shaded dolomite boulders are themselves an uncom- mon occurrence in Michigan, it is also likely that these boulders provide a unique environment for bryophytes. It is the purpose of this study to determine the bryophytes associated with the hart’s tongue fern and to examine possible re- 6 THE MICHIGAN BOTANIST Vol. 41 lationships they might have with the fern as an indication of topics needing fur- ther study in the quest to protect these endangered plants. METHODS In July 1993, we visited two hart’s tongue fern sites (Taylor Creek and East Lake, Mackinac County, MI), guided by Dorothy Evans of the U. S. Department of Agriculture, Forest Service, Es- canaba, MI, and compiled a species list for the bryophytes. Our primary objective was to determine what comprised the typical communities and to examine the rocks for unusual bryophytes. At the same time, we looked for clues as to any possible role the bryophytes might play in the success of the fern, particularly in the gametophyte stage. We sampled 21 plots at East Lake and 39 plots at Taylor Creek. Whenever possible, we re-lo- cated the plots previously marked and numbered for the fern study by staff of the Forest Service, Es- canaba, MI. Plots consisted of a radius of influence of ca. 15 cm. In addition, we listed any species seen but not within the circle of influence. Since the ferns were almost exclusively on the sides of boulders, mosses occurring on the tops of the boulders were outside the circle of influence, but all of these appeared at some location within the circle of influence around a hart’s tongue fern. Nomenclature follows Anderson et al. (1990) for mosses, Crum (1991) for liverworts, and Flora of North America Editorial Committee (1993) for ferns. Voucher specimens of bryophytes are de- posited in the cryptogamic herbarium of Michigan Technological University (MCTC) and with the U.S. Department of Agriculture, Forest Service, Escanaba, MI. RESULTS AND DISCUSSION Bryophyte associations Nineteen species of bryophytes were found in association with the hart’s tongue fern on the boulders. Seventeen were present at East Lake; eleven were present at Taylor Creek (Table 1). Seven species that occurred on only one or two rocks in association with ferns at East Lake were absent from Taylor Creek despite the larger number of samples there; only two species from Taylor Creek were present in only one or two associations and absent from East Lake. Thus, nine abundant species were common to both sites. Most of the rocks were completely covered by bryophytes, with only small areas of recent disturbance that provided areas of exposed rock. Several species dominated the rocks: Anomodon attenuatus, Brachythecium rutabulum, Brachythecium sp., Plagiomnium affine, Thuidium recognitum. Only Anomodon attenuatus (12% of NY samples collected) was in common with the dominant bryophytes in the New York study (Cinquemani Kuehn & Leonard 1993), which together with Brachythecium oxycladon (Brid.) Jaeg. & Sauerb. (42%), Mnium cuspidatum Hedw. (24%), and Eurhynchium pulchellum (Hedw.) Jenn. (12%) comprised the most common NY taxa. Since all of these taxa are common in this geographic area, the overlap of only one common species suggests that condi- tions most likely are different. Plagiothecium laetum was common in a narrow zone at the bases of rocks, especially at Taylor Creek. Examination under the microscope revealed several taxa that were not seen in the field: Platydictya confervoides, Homalia tri- chomanoides, Lophozia barbata. The development of a species list was compli- 2002 THE MICHIGAN BOTANIST 7 TABLE 1. Percent frequency of bryophyte species from circle of influence plots at East Lake (21 plots) and Taylor Creek (39 plots). East Lake Taylor Creek Anomodon attenuatus (Hedw.) Hüb. 33 33 Anomodon rostratus (Hedw.) Schimp. 5 Barbilophozia barbata (Schreb.) Loeske 10 Brachythecium shiny 71 59 Brachythecium rutabulum (Hedw.) Schimp. in B.S.G. 33 31 Cephalozia sp. 5 Cephaloziella rubella (Nees) Warnst. 5 Dicranum scoparium Hedw. 5 Fissidens adianthoides Hedw. 19 13 Homalia trichomanoides (Hedw.) Schimp in B.S.G. 5 Mnium marginatum (With.) Brid. ex P. Beauv. 10 21 Plagiochila porelloides (Torr.) Lindenb. 10 Plagiomnium affine (Bland. ex Funck) T. Kop. sensu lato 14 74 Plagiothecium laetum Schimp. in B.S.G. 19 44 Platydictya confervoides (Brid.) Crum 5 Porella platyphylla (L.) Pfeiff. 3 Rhodobryum ontariense (Kindb.) Par. in Kindb. 14 10 Thuidium recognitum (Hedw.) Lindb. 57 46 Tortella tortuosa (Hedw.) Limpr. 5 cated by the low light at the sites and the restrictions on collecting that were nec- essary in order to protect the fern sites for future expansion. It is likely that other small taxa, especially leafy liverworts, were not located. The bryophytes seem to exhibit a zonation pattern that is worthy of further study. The tops of the rocks and a considerable distance down the sides are cov- ered by Brachythecium rutabulum and a second undetermined species that ap- pears to be a different, smaller, shiny Brachythecium. On some rocks, the top is covered instead by Thuidium recognitum. Below that is a zone of Anomodon at- tenuatus. Near the bases of many of the rocks there is a narrow band of Plagio- thecium laetum. The hart’s tongue fern seems to be concentrated in the middle and bottom zones. Patchiness Fissidens adianthoides and Mnium marginatum tend to occur as invaders in disturbed patches where large clumps of the dominant pleurocarpous mosses such as Brachythecium, Thuidium, Plagiomnium, and Anomodon have been torn off. Kimmerer & Allen (1982), studying disturbed patches of sandstone cliffs, observed similar patterns for Fissidens obtusifolius where large, intertwined bryophytes had been torn off. As on the boulders, the dominant cliff species oc- curred in distinct vertical zones, whereas all species had a patchy distribution on open spaces that had resulted from disturbance. Fissidens obtusifolius had the greatest cover in the low, most disturbed cliff zone, whereas Conocephalum con- icum was virtually absent there. Kimmerer & Allen concluded that its absence was due to severe disturbance, where large, intertwined, weakly attached patches 8 THE MICHIGAN BOTANIST Vol. 41 were removed as a group. The smaller, upright Fissidens, on the other hand, had individual plants strongly attached by rhizoids and was not intermingled, there- fore not losing large masses at one time. In undisturbed areas, F. obtusifolius was easily overgrown by C. conicum. In more stable areas, Gymnostomum aerugi- nosum and Mnium marginatum occurred in the same zones as the Cono- cephalum, but they were not dominants. On the dolomite boulders of the present study, as with C. conicum, when any part of the larger pleurocarpous mosses is detached, it is likely to take with it a large portion of the adjoining clone. Establishment of F. obtusifolius in areas of disturbance can occur within 30 days, but the percent cover drops to less than 10% within one year (Kimmerer & Allen 1982). At the dolomite boulders, it is likewise a species of Fissidens, F. adianthoides, that is the primary invader of disturbed patches. Likewise, in some of these, Mnium marginatum is a common invader, occurring only where the thick moss mats had detached. The one large mat-forming species that enters early in this post-disturbance succession is Thuidium recognitum, but in its early stages of development it has a growth form not very different from that of the Fissidens or Mnium. On the sandstone cliffs, the Fissidens was not replaced with Fissidens, but rather by a group of intermediate successional species: Brachythe- cium rutabulum increased sixfold and Gymnostomum aeruginosum increased threefold (Kimmerer & Allen 1982). It was not clear which of the pleurocarpous mosses invaded next on the limestone boulders, but it appeared that the most likely event was invasion by the existing mosses at the periphery of the distur- bance patch.