2009 NORTHEASTERN NATURALIST 16(1):67–84
Relationship of Bryophyte Occurrence to Rock Type in
Upstate New York and Coastal Maine
Natalie L. Cleavitt1,*, Susan A. Williams2, and Nancy G. Slack3
Abstract - Bryophytes are often noted for their growth on specific rock types and
their value as indicator species. However, some evidence suggests that restriction of
a species to specific rock types may be less rigid and could vary under different environmental
conditions. We assessed richness and distribution patterns of bryophytes
at 22 rock outcrop locations in upstate New York (NY) and coastal Maine (ACAD).
At each location, detailed surveys were done in five replicate 5-m by 2-m plots on
vertical rock faces. We report on the 194 bryophyte species found in these surveys
and present detailed analyses for the 137 species that occurred at two or more of the
22 locations. In general, liverworts were less likely to be dominant within a plot than
mosses. Within-site dominance and frequency of liverworts were less well correlated
to larger-scale frequency (number of locations and regions of occurrence). In NY,
although there was no significant difference in bryophyte richness by rock type, rare
species were more often found on calcium-containing rock types. Rock type, soil
influence, number of liverwort species, and region were significant correlates with
bryophyte species composition patterns. The importance of rock type in explaining
species composition patterns was still significant though weaker when ACAD locations
were included in the analysis. This difference resulted from a higher prevalence
of leafy liverwort species on calcium-containing rock types in ACAD. Our results
present further evidence that apparent restrictions to specific rock types may shift
depending on environmental conditions such as increased humidity and narrower
temperature extremes that occur along the north Atlantic coast.
Introduction
Bryophytes represent a unique component of the richness, structural
complexity, and functioning of many community types in the northeast.
Rock-outcrop communities are notable upland assemblages in which
bryophytes can dominate as the main vegetation. The role of rock type in
determining bryophyte assemblages is well known from Europe (e.g., Bates
1978, Smith 1982), but is less well studied in North America, and then
mainly in western North America (e.g., Cleavitt 2001, Horton 1988, Shaw
1981). Although many bryophyte floristic surveys have been conducted in
the regions of upstate New York and coastal Maine (e.g., Allen 2005, Ketchledge
1980, Patterson 1930, Schuster 1949), none have focused specifically
on rock-outcrop communities through a standardized sampling protocol, and
the communities remain under-documented.
Remarkably different bryophyte assemblages can be present within close
proximity when calcareous and non-calcareous rock types are juxtaposed
1Department of Natural Resources, 8F Fernow Hall, Cornell University, Ithaca, NY
14853. 2340 Maple Street, Hinsdale, MA 01235. 3Biology Department, The Russell
Sage Colleges, Troy, NY 12180. *Corresponding author - nlc4@cornell.edu.
68 Northeastern Naturalist Vol. 16, No. 1
on the landscape (Bates 1978, Miller and McDaniel 2004). Smith (1982)
presented results from several European studies demonstrating the relationship
between bryophyte species assemblages and rock type. In particular,
limestone had a more specific flora than the non-calcareous rock types
(Bates 1978, Smith 1982). Wide tolerance for substrate chemistry has been
correlated with common or widespread species, and pH was the strongest
explanatory variable separating the habitats of species (see results of Shaw
[1981] for Pohlia and Horton [1988] for Encalypta). Jenkins (2004) observed
that six rare bryophytes found in the Adirondack Park of New York all
occur on “limy” ledges. Recent work on bryophyte communities in eastern
Europe has shown that calcium-containing rock types contain higher overall
species richness; however, liverwort species richness was higher on noncalcareous
rock types (Kubešová and Chytrý 2005).
The variation in substrate specificity throughout the range of a given
bryophyte species may be underappreciated. For instance, species have been
documented to shift from mainly tree-dwelling to rock-dwelling at their
range limits (Piippo 1982, Smith 1982) and species can also demonstrate
regional preference for calcium depending on pollution influence (Bates
1993). In the Gulf of St. Lawrence region, influence of rock type (areal
extent of calcareous rock outcrops) was secondary to climatic factors such
as growing-season temperature and ocean influence for explaining species
distributions (Belland 2005).
In this study, we examined patterns in bryophyte species occurrences on
a range of rock types in upstate New York (NY), and then tested to see if species
exhibited the same patterns on these rock types in coastal Maine (Acadia
National Park; ACAD). We had four main questions (Q) and hypotheses (H).
Q1) What are the main correlates to bryophyte species composition at 19 NY
locations? H1) Sites would separate most strongly along a rock-type gradient
by degree of calcium content. Q2) Do patterns of bryophyte species composition
found in NY hold for similar rock types in ACAD? H2) Maine sites would
follow the bryophyte composition patterns found in NY. Q3) How do species
richness and rare species occurrences compare between sites and rock types in
the three regions of NY? H3) More rare species and higher bryophyte species
richness would occur on calcium-containing rock types. Q4) Do mosses and
liverworts differ in their prevalence on different rock types or in their frequency
and abundance patterns? H4) Liverworts would be comparatively more prevalent
on non-calcareous rock types. Their frequencies would be similar to those
of mosses, but their abundances would be lower than mosses given the generally
smaller size of liverworts.
Methods
Site selection
In NY, six rock outcrops were surveyed in each of the three regions: the Adirondack
Mountain region in the northeast (Adirondacks), the Catskill Mountain
and Shawangunk Mountain region in the southeast (Catskill-Shawangunk),
2009 N.L. Cleavitt, S.A. Williams, and N.G. Slack 69
and the Finger Lakes region in the center (Finger Lakes) (Fig. 1, Table 1). One
additional site from the mid-eastern section of the state was also included for a
total of 19 sites in NY. Rock outcrops in the Adirondacks were all at relatively
lower elevations for that region and were comparable with the elevations of
rock outcrops in the other two regions. Three locations were surveyed in
ACAD, with two sites on Isle au Haut and the third on Mount Desert Island
(Fig. 1, Table 1). N.L. Cleavitt and S.A. Williams surveyed NY locations from
June to September 2005 and ACAD locations in August 2006.
Site-selection protocol required that: 1) rock outcrops were in a wooded
landscape such that all rock outcrops received some shading from the tree
canopy, and 2) the rock-outcrop complex was large enough to accommodate
our plot-selection methods (five rock outcrops with a vertical face at least
2 m high by 5 m wide). In addition, site selection was designed to include a
range of rock types with equal representation of calcareous and non-calcareous
rocks. Initial rock-type designations for site selection were made using
information provided by the NY Heritage Element Occurrence Records for
“Cliff Communities” (on file with NY State Heritage Program, Albany, NY)
for NY locations, and Gilman and Chapman (1988) for ACAD locations. Final
rock-type descriptions included in Table 1 were made from rock samples
taken from each site. Samples were examined by Professor William Bassett
(Geologist, Cornell University, Ithaca, NY) using HCl tests for calcium carbonates
and a dissecting scope to ascertain mineral composition and degree
of weathering. Surveyed rock types in NY varied from base-poor quartzite
and conglomerates (Catskill-Shawangunk) to calcareous limestone, shales,
and sandstones (Finger Lakes). The Adirondack rock outcrops included
Figure 1. Locations of 22 sites where rock outcrops were surveyed for bryophytes
in New York (19 sites) and Maine (Acadia National Park, 3 sites). In NY, sites were
selected in three regions: Adirondack Mountains (4R, DL, HM, LD, PL, WH);
Catskill-Shawangunk Mountains (BC, BLT, MRTP, NL, OM, TR); and Finger Lakes
(BF, CF, LB, LSP, SB, TEG). TP was an additional limestone site in mid-eastern NY
just north of the Catskill Mountain sites.
70 Northeastern Naturalist Vol. 16, No. 1
the widest diversity of rock types from limestone to granite (Table 1). The
ACAD rock outcrops included granite, volcanic tuffs, and gabbro-diorite.
Plot surveys
Within each site, five replicate plots 2 m high by 5 m wide were surveyed
on vertical rock outcrops. Selection for plot locations was "restricted random,"
with the restrictions being that the first five plots encountered that met
the following criteria were surveyed: 1) greater than 1-m2 cover of bryophytes,
Table 1. Sites, grouped by region, where rock outcrop surveys were conducted in New York and
Maine. Site locations are given in Figure 1. Site abbreviations are used in Figures 1 and 2. Rock
types were determined from rock samples taken at each site.
Site (abbreviation) Aspect Rock type
Adirondack Mountains (A), NY
Deer Leap (DL) E Gneiss containing quartz, unaltered feldspars,
magnitite and iron
Huckleberry Mt. (HM) NNE Well-crystalized granitic gneiss
Little Diameter (LD) SSW Gneiss containing amphibolite bands
Peltigera Rock outcrop (PL) ESE Calcite inclusions and high calcium carbonate
content, formation also containing muscovite,
sheet-silicates and mica crystals
River Road, RR (4R) SE Well-crystalized granitic gneiss
Warner Hill (WH) W Limestone
Catskill-Shawangunk (C)
Blue Rock outcrop Trail (BLT) NNW Arkose sandstone derived from granite and
encompassing different degrees of weathering
of feldspars to clay
Bonticou Crag (BC) N Quartzite
Mt. Road - Taconic Pkwy. (MRTP) W Mudstone (shale with some schist components),
hematite stained sheet silicates containing
chlorite, quartz and mica, no carbonates
North Lake (NL) W Arkose sandstone derived from granite and
encompassing different degrees of weathering
of feldspars to clay
Overlook Mt. (OM) W Arkose sandstone, highly weathered and containing
talc, biotite and iron stained silicates
Table Rocks (TR) NNE Quartzite
Finger Lakes (F)
Buttermilk Falls (BF) NNE Calcareous shale and mudstone
Chittenango Falls (CF) NNE Limestone
Letchworth State Park (LSP) E, N Calcareous mudstone
Lick Brook (LB) NNE Calcareous shale and mudstone
Stony Brook (SB) ESE Calcareous shale and mudstone gorge; band of
schist lacking carbonates
Treman/Enfield Glen (TEG) NE Calcareous shale and mudstone gorge
Additional NY site:
Thacher State Park (TP) NNE Limestone of the Helderberg Escarpment
Acadia National Park, Maine (ACAD)
Long Pond (MELP) E Gabbro-diorite (calcium containing igneous
rock)
Duck Harbor Mt. (MEDH) NW Volcanic tuffs mixed with some calcite crystals
Mansell Mt. (MEMM) N, NE Coarse granite with feldspars (non-calcareous)
2009 N.L. Cleavitt, S.A. Williams, and N.G. Slack 71
2) at least 2 m high, 3) no soil areas with vascular plant cover, and 4) at least
5 m away from the last surveyed plot. Per plot, a species tally was gathered
and an asterisk was placed by all species that achieved greater than 100 cm2
cover (a 10-cm x 10-cm transparent grid divided into 1-cm2 cells was used for
reference) within an individual plot. For a given site, a species could then be
“dominant” at 0–5 of the plots in the site. While not a detailed cover estimate,
this method is repeatable and not overly time demanding while providing a
useful quantification of species’ relative importance on the rock outcrops.
Each plot was surveyed by both S.A. Williams and N.L. Cleavitt, with each
person starting at opposite ends and crossing roughly in the middle to finish
where the other person began. Complete sets of vouchers were collected for
each site, with additional collections within a site for species that lacked good
field characters. This work is based on the collection of over 1200 voucher
specimens deposited at New York State Museum (NYS), New York Botanical
Garden (NYBG), Bailey Hortorium at Cornell University (BH), and College
of the Atlantic Herbarium (HCOA; designated ACAD repository).
Data analyses
The relationship between species composition of sites was analyzed
using non-metric multidimensional scaling (NMS) in PC-ORD (ver. 4.27).
The NMS analysis is an ordination method that uses an iterative search for
rankings and placement of the analyzed variables to find the solution that
minimizes stress (McCune and Mefford 1999). Because NMS uses ranks, it
can be considered a non-parametric form of ordination with relaxed assumptions
on data structure that are usually more applicable to ecological data
(McCune and Mefford 1999). All NMS analyses were run using Sorensen’s
distance measure with 40 runs using real data and 50 runs of randomized
data. The instability criterion was 0.00001, with 400 as the maximum number
of iterations. The final solution was chosen based on the dimensionality
with the lowest mean stress from a run comparing randomized to real data
(McCune and Mefford 1999).
Two ordinations were run: 1) a dataset including 134 bryophyte species
that occurred at more than one site was used for NY sites only, and 2) a dataset
of 137 species occurring at two or more of all 22 sites (Appendix A). The
frequency of a species within a site (number of the five plots where the species
was present) was used as the abundance value in the ordination data set. The
correlation of available site variables was examined by overlaying joint plot
vectors onto the ordination calculated from the species composition data. The
explanatory values are expressed as correlation (r2) to the ordination axes.
Visually, vectors represent the hypotenuse of a right triangle with adjacent
and opposite sides being the r2 values to the two axes displayed (McCune and
Grace 2002). Therefore, both the length and angle of the vector express information
about the strength of the variable’s correlation to the axes.
For the vector joint plot, rock type, region, degree of soil influence
(cover classes on surveyed areas), total richness of bryophytes, and number
of liverwort species were entered. The rock types were coded as: quartzite,
72 Northeastern Naturalist Vol. 16, No. 1
weathered sandstone and gneiss, sandstone and gneiss with feldspars still
present, igneous calcium-containing rocks, calcium-rich mudstones and
shales, and limestones. Regions were coded as: Adirondacks, Catskills-
Shawangunks, Finger Lakes, or ACAD.
Differences in species richness, number of rare species, and number of
liverworts between calcareous and non-calcareous rock types was tested by
one-way ANOVA. One site (Warner Hill [WH]) was excluded from these
analyses because it had very high variability in species richness, which resulted
because one of the five restricted-random rock outcrop sections had
100% dominance of a single species. Using histograms and Mann Whitney
U-tests, differences between liverworts and mosses were examined for frequency
between and within sites and dominance within sites . All non-ordination
analyses were preformed in SPSS ver. 14.0. All means are presented
with ± 1 SE of the mean.
A list of species that occurred at only one NY site is given in
Appendix B. Twelve species present at ACAD were absent from NY sites
(Appendix B). Because of the potential that they are coastally restricted,
these species were left out of the ordination data set, so that they would
not cause the Maine sites to cluster together. Rare species designations for
NY are based on Cleavitt et al. (2006). Nomenclature follows Crosby et al.
(1999) for mosses and Schuster (1966–1992) for liverworts.
Results
Correlates to bryophyte composition at NY sites
Although only the ordination from the full 22-site analysis is shown, the
patterns in Figure 2 are also representative of patterns for NY sites alone.
Tables 2 and 3 give details on the minor changes between the ordinations.
Two main patterns emerged from the NMS ordinations: 1) species composition
separated along a rock-type and soil-influence gradient (Fig. 2), and
2) liverworts separated out significantly toward sites with non-calcareous
rock types (Fig. 2). In the NY site ordination, both axes relate to rock types,
with the ends of the gradient in species composition as three limestone (WH,
TP, and CF) and the two quartzite sites (BC and TR) (Table 2a, Fig. 2). There
were a total of 182 bryophyte species verified from the NY sites, with 141
mosses and 41 liverworts. Of these species, 134 (101 mosses, 33 liverworts)
occurred at two or more of the 19 survey sites (Appendix A), and these were
used in the ordination analysis. For the NMS ordination, a two-dimensional
solution was best, with relatively low stress (9.51) and instability (p less than
0.0001) indicating a robust ordination appropriate for ecological interpretation
(McCune and Grace 2002).
Species with high indicator value (i.e., Pearson’s r value indicated
a significant correlation) for non-calcareous rock outcrops included:
Andreaea rothii (0.636), Blepharostoma trichophyllum (0.625),
Dicranum fulvum (0.919), Dicranum montanum (0.831), Jamesoniella
autumnalis (0.676), Leucobryum glaucum (0.716), Plagiothecium laetum
2009 N.L. Cleavitt, S.A. Williams, and N.G. Slack 73
(0.618), Pohlia nutans (0.729), Pseudotaxiphyllum distichaceum (0.659),
Pylaisiadelphus tenuirostris (0.749), and Scapania nemorea (0.800). Species
with higher indicator value (r value) for calcium-containing rock outcrops
included: Fissidens bryoides (0.723), Brachythecium oxycladon (0.618),
Campylium chrysophyllum (0.676), Encalypta procera (0.666), and Myurella
sibirica (0.680).
Differences between NY and ACAD composition patterns
We found a total of 67 bryophyte species at ACAD, of which 22 were
leafy liverworts. A total of 194 bryophyte species were present in the
combined site checklists (148 mosses, 46 liverworts) (Appendices A and
B). Of these, 137 species (103 mosses, 34 liverworts) occurred at two or
Figure 2. Ordination (calculated by non-metric multidimensional scaling) showing
the relative similarities and differences in bryophyte species composition for 22 sites
in New York and Maine and joint bi-plot with site characteristics. Site abbreviations
are those from Table 1. Site abbreviations for Maine sites begin with ME. Sites are
coded here by rock-type: ▲ = limestones, ♦ = calcareous mudstones and shales, ●
= igneous calcium-containing rocks, ° = sandstones and gneiss with feldspars, Δ =
weathered sandstones, gneiss and granites, ◊ = quartzite. Vectors represent the correlation
of variables to the ordination axes. Significantly correlated variables were
rock type (six rock type classes as coded above), soil (degree of soil influence), region
(four study regions), and liverworts (the number of liverworts). Table 3 contains
further details of vector correlation significance.
74 Northeastern Naturalist Vol. 16, No. 1
more of the 22 survey sites, and these species were used in the correlation
and ordination analyses. The NMS ordination was robust (10.345 = final
stress for 2-dimensional solution, 0.00001 = final instability) and explained
91.6% of the variation in bryophyte species composition (Fig. 2).
The most notable changes from the ordination with NY sites only were
the increased importance of region in explaining variation along axis 2,
and the coincident lack of correlation for rock type and soil influence
with the second axis (Table 2b). The pattern of liverwort prevalence toward
the positive end of axis 1 (non-calcareous rock types) is equally
strong in both ordinations (Table 2).
As in NY, liverworts accounted for a higher proportion of the bryophyte
flora on non-calcareous rock outcrops in ACAD. Mansell Mountain (granite)
rock outcrop flora was 39.5% liverworts, Duck Harbor (volcanic tuffs)
was 32.5%, and Long Pond (gabbro-diorite) was 26.5%. However, liverworts
contributed two-times more to the flora on calcium-containing rock
Table 2. Correlation of site traits to the two ordination axes from non-metric multidimensionsal
analyses.
a) For NY sites (n = 19).
Axis 1 Axis 2
Trait Pearson’s r Significance Pearson’s r Significance
Rock type -0.930 <0.001 -0.724 <0.001
Region 0.026 ns -0.553 <0.020
Soil influence -0.668 <0.01 -0.807 <0.001
Total species -0.397 ns -0.161 ns
No. liverwort spp. 0.668 <0.01 0.326 ns
b) For NY and ACAD sites combined (n = 22). Significant relationships are displayed as vectors
on Figure 2.
Axis 1 Axis 2
Trait Pearson’s r Significance Pearson’s r Significance
Rock type -0.915 <0.001 0.110 ns
Region 0.136 ns -0.576 <0.01
Soil influence -0.827 <0.001 -0.107 ns
Total species -0.331 ns 0.182 ns
No. liverwort spp. 0.684 <0.001 -0.359 ns
Table 3. Correlations between averages for number of regions, number of sites, and frequency
and dominance within sites for mosses (below diagonal; n = 103) and liverworts (above diagonal;
n = 35). Values are given in Appendix A. Histogram summaries are shown in Figure
3. Significance values are given as superscripts: ns = not significant at P = 0.05; * denotes P <
0.05; ** P < 0.01; and *** P < 0.001.
Regions Sites Frequency Dominance
Regions 0.777*** 0.326ns 0.196ns
Sites 0.751*** 0.560*** 0.368*
Frequency 0.444** 0.627*** 0.620***
Dominance 0.201* 0.356** 0.550***
2009 N.L. Cleavitt, S.A. Williams, and N.G. Slack 75
outcrops in ACAD than in NY (for NY: N = 10, % liverworts = 13.5 ± 6.3),
and this trend is also evident in the placement of ACAD sites on the ordination
(Fig. 2). All three Maine sites clustered with the non-calcareous rock
floras of upstate NY regardless of rock type (Fig. 2).
Patterns of species richness in NY
Species richness did not differ significantly between rock types (noncalcareous:
34.7± 3.21, calcareous: 39.7 ± 3.12; F1,17 = 1.25, P = 0.281),
although there were significant differences in richness between sites (P <
0.001; range = 23–54 species). Mean species richness within the 2-m by
5-m plot area ranged from 9.2 ± 1.1 to 26.6 ± 2.4 species. The three NY
regions (each with six survey sites) had comparable species richness on
rock outcrops, with the Adirondacks (109 spp.) and Finger Lakes (107 spp.)
regions slightly higher than the Catskill-Shawangunk (97 spp.) region. The
Finger Lakes had the highest number of species found only in that region (24
spp.) and also had the greatest number of rare species (8 spp.) based on the
updated NY rare moss list (Cleavitt et al. 2006). Although the Finger Lakes
has the most unique species on a regional scale, within the region there is
a higher number of shared species (41 spp. occurring at four or more of
the six sites) than within the other two regions (Adirondacks: 14 spp., and
Catskill-Shawangunk: 19 spp.). The high number of shared species in the
Finger Lakes relates at least in part to the greater homogeneity in rock types
compared to the other two regions.
The number of rare species was significantly higher on calcareous (2.13
± 0.44) relative to non-calcareous rock outcrops (0.78 ± 0.32; F1,16 = 6.26,
P = 0.024). Fifteen moss species regarded as rare in NY were found during
the rock outcrop surveys and two of these species, Tortula pagorum and
Fabronia ciliaris, were only recently reported for NY (Cleavitt et al. 2006,
Trigoboff 2005) (Appendices A and B). Three of the other 13 species were
collected at three or more of the sites and they may be more widespread than
herbarium records indicate (Appendix A). The other ten species are split
evenly between S1 (1–5 occurrences in NY) and S2 (6–20 occurrences in
NY) ranks (Appendices A and B). Only three of the rare mosses— Pseudotaxiphyllum
distichaceum, Schwetschkeopsis fabronia, and Sematophyllum
demissum— were collected from non-calcareous rock types; therefore, 80%
of the rare species were on calcium-containing rocks.
Differences between mosses and liverworts (all sites)
Liverworts accounted for a significantly higher percentage of species
richness at non-calcareous rock outcrops (10.2 ± 1.04%) than at calcareous
rock outcrops (5.89 ± 0.87%) (F1,17 = 10.2, P = 0.006). Mosses were dominant
more often than liverworts within a site (Mann Whitney U: z = - 2.245,
P = 0.025; Fig. 3). There were no significant differences between mosses and
liverworts for the within-site frequency or the number of sites of occurrence
(Fig. 3). Frequency and dominance within a site were significantly correlated
with higher frequency at both the site and regional scales for mosses. For
76 Northeastern Naturalist Vol. 16, No. 1
liverworts, within-site frequency and dominance were not correlated with
the number of regions of occurrence (Table 3).
Figure 3. Histograms
of moss (left) and liverwort
(right) species
occurrences with average
values (± standard
errors), for all sites in
New York and Maine.
A. Species distribution
by the number
of sites of occurrence
(possible values are
2–22). B. Species distribution
by their frequency
within sites
as the average value
across sites (for each
site the possible values
are 1–5 plots). C.
Species distributions
by dominance within
sites as their average
values across sites (for
each site the possible
values are 0–5, where
5 would mean greater
than 100 cm2 cover
at all five plots within
a site).
2009 N.L. Cleavitt, S.A. Williams, and N.G. Slack 77
Discussion
Most of our original hypotheses were supported by the results of this
study, with the exceptions that the ACAD sites did not ordinate with the NY
sites that had similar rock types and the number of liverworts was a stronger
correlate to the composition of bryophyte rock outcrop assemblages than
initially anticipated. Although rock type was the strongest correlate to axis
1, which explained 80.5% of the variation in the data, the two calcium-containing
rock types in ACAD were closest in bryophyte species composition
to the non-calcareous rock types from New York. This pattern resulted from
the greater importance of leafy liverworts on all three of the ACAD sites.
The higher humidity, including frequent fogs along the coast, may promote
leafy liverwort growth and allow these species to compete well on all
rock types in ACAD. This hypothesis is partially supported by the restriction
of Isothecium stoloniferum and Aulocomnium androgynum to the coastal
rock cliffs (species included in Appendix B). These species were found by
Hedderson and Brassard (1990) to be mainly limited by moisture availability.
The exclusion of most leafy liverwort species from calcareous rock types
in NY may be due at least in part to differences in the water-holding capacities
or water-retention times of the rocks rather than wholly to differences
in rock chemistry (Aho and Weaver 2006). In contrast to leafy liverworts,
the thalloid liverworts only occurred on calcium-containing rock types in
this study, but their contribution to species composition patterns was small
(Appendices A and B). This unanticipated pattern in the occurrence of leafy
liverworts demonstrates the complexity of species ecology and suggests that
apparent substratum specificity or restrictions may change under different
climate regimes.
Our finding of a lower proportion of liverwort species relative to mosses
on calcareous rocks agrees with a recent paper by Kubešová and Chytrý
(2005) and is the first quantification of this pattern for northeastern North
America. Our results differed from that study in that we did not find higher
species richness on calcium-rich rocks. This discrepancy may partly be due
to a difference in methodology. Kubešová and Chytrý (2005) conducted
plotless site surveys and found the number of species to increase with cliff
area, while we restricted ourselves to the same amount of rock outcrop area
at each site. Therefore, while we often noted additional species between
surveyed areas, these were not included in the data set presented here.
In addition, Kubešová and Chytrý (2005) note that base-rich rock may
have a larger range of pH when sampling includes the more base-poor organic
soil components. Our methodology limited the amount of such area
included to more closely reflect rock chemistry and to target areas without
vascular plants, since in such areas bryophyte richness may be lowered by
competition (Kuntz and Larson 2006). We interpret soil influence in our
study as representing differences in the amount of fracturing and small
cracks. The calcareous mudstones and shales were among the most friable
rock types and tended to have mineral soil coating the rock surfaces as well
78 Northeastern Naturalist Vol. 16, No. 1
as filling the many small cracks of the rock layers. Rock texture and friability
are additional rock characters, other than rock chemistry, that may account
in part for some species occurrences on specific rock types.
Previous studies comparing bryophyte assemblages across rock types
have suggested that limestone had the most unique flora (Bates 1978, Smith
1982). In particular, Bates (1978) conducted work most similar to ours by
investigating the bryoflora and chemical signatures of four rock types in
Scotland (limestone, acid sandstone, basalt, and ultrabasic rock). While
the limestone flora was quite distinct from the flora on the other three rock
types, Bates (1978) noted that inclusion of other base-rich sedimentary
rocks might make limestone flora appear less differentiated. Our ordination
clearly shows this caveat to be correct, with species composition showing
a continuous gradient. Without the calcareous mudstone and shale floras,
there would have been a large gap in species composition between igneous
calcium-containing rocks and limestone, which still forms the end of the
calcium-rich gradient (Fig. 2).
Our results were similar to Bates (1978) in that no taxon was abundant on
all rock types. The most ubiquitous species that we found were Anomodon
rostratus, A. attenuatus, Dicranum fulvum, Plagiothecium cavifolium,
Pseudotaxiphyllum elegans, and Scapania nemorea. The two species of
Anomodon were absent from the most base-poor rocks (quartzite, granites,
and weathered calcium-poor sandstone and gneiss) and tended to increase in
abundance on calcium-rich rocks. In contrast, Dicranum fulvum and Scapania
nemorea were absent from the most calcium-rich rocks (limestones and
calcareous mudstones and shales) and increased in abundance on calciumpoor
rock types. Both are indicator species for base-poor rock. Plagiothecium
cavifolium and Pseudotaxiphyllum elegans were absent from the most
basic and the most base-poor rock types, but were abundant elsewhere.
While bryophyte assemblages in the northeastern US do show strong
separation along a rock-type gradient, the reliability of certain species
as indicators of calcium status should be treated with caution for several
reasons. Firstly, calcium content of the rock may not be the sole reason for
species presence on a rock outcrop. Other important factors to consider are:
1) influence of local climate, 2) importance of rock water relations, and
3) modification of the rock environment by micro-topography (e.g., overhangs,
underhangs, crevices) or soil presence. Some species do appear to be
robust indicators, if not specifically of calcium status, then more generally
of rock pH. For instance, the resolution of Encalypta procera as an indicator
species for base-rich rock agrees with the findings of Hedderson and Brassard
(1990) for this species in Newfoundland. Andreaea spp. are also well
documented as indicators of acid rock types (Heegaard 1997).
As suggested by Jenkins (2004), calcareous rock types supported a
larger number of rare moss species in NY than non-calcareous rock types.
Rare liverworts were not included in this analysis since they are not yet assessed
for NY. Many of the rare species for this study (only present at one
NY site; Appendix B) were found only on calcium-containing rock types.
2009 N.L. Cleavitt, S.A. Williams, and N.G. Slack 79
The NY species with S1 or S2 ranks from calcareous rocks included: Conardia
compacta, Cyrto-hypnum pygmaeum, Didymodon ferrugineus, Mnium
ambiguum, Platydictya jungermannioides, Seligeria calcarea, Seligeria
donniana, and Taxiphyllum taxirameum (Appendices A and B). Conservation
of bryophytes on rock outcrops in the northeast US may be guided in
part by the following general conclusions: 1) calcareous rock types support
more rare moss species than non-calcareous rock types, 2) non-calcareous
rock outcrops are critical for leafy liverwort species richness, and therefore,
3) protection of habitat that includes the full range of rock types present in a
region would more fully protect rock bryophyte assemblages than focusing
on a single rock type.
Acknowledgments
Funding for this research was provided through the New York State Biodiversity
Research Initiative to N.L. Cleavitt, S.A. Williams, and N.G. Slack, and an L.L. Bean
Acadia Research Fellowship to N.L. Cleavitt and S.A. Williams. We are grateful to:
David Werier for preparing Figure 1 and helping with site visits around the Finger
Lakes region; Professor William A. Bassett of the Department of Earth and Atmospheric
Sciences, Cornell University, for identifying rock samples for the summaries
provided in Table 1; Alison C. Dibble for assisting with fieldwork on Isle au Haut and
providing comments on a previous version of the paper; Troy Weldy and Greg Edinger,
New York Natural Heritage, for providing access to information for selection
of NY locations; Wayne Barder, Stuart West, and David Manski of Acadia National
Park for making our visit to Isle au Haut and survey work in Acadia both pleasant and
possible; Jerry Jenkins for assisting with several site visits in the Adirondacks region,
and particularly for canoe transport to WH; Steve Rice, Union College, for acting as
guest editor on this paper; and two anonymous reviewers for helpful suggestions.
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Appendix A. Summary table of the 137 bryophyte species included in the ordination for 22
sites occurring on rock outcrops. Rare species are indicated by a superscript with their S-rank
for NY. R = regions of occurence, which are abbreviated as: A = Adirondacks, C = Catskill-Shawangunk,
F = Finger Lakes, and M = ACAD, Maine. Frequency is the number of cliff sections
(maximum of 5) within a location in which the species occurred. Dominance is the number of
sections (maximum of 5) within a location where the species cover was greater than 100 cm2.
No. Average Average
Species sites frequency dominance R
Mosses
Amblystegium serpens (Hedw.) Schimp. 3 1.0 0.5 AC
A. varium (Hedw.) Lindb. 3 2.3 0.3 AF
Amphidium lapponicum (Hedw.) Schimp. 2 1.0 0.0 CF
A. mougeotii (Bruch. & Schimp.) Schimp. 4 1.8 0.0 CM
Andreaea rothii F. Weber & D. Mohr. 7 3.4 1.8 ACM
A. rupestris Hedw. 5 3.4 0.7 CM
Anomodon attenuatus (Hedw.) Huebener 13 3.1 1.0 ACF
A. rostratus (Hedw.) Schimp. 16 3.2 1.1 ACFM
A. viticulosus (Hedw.) Hook. & Taylor 5 3.0 1.8 AF
Atrichum angustatum Bruch & Schimp. 2 1.0 0.0 F
A. oerstedianum (Müll. Hal.) Mitt. 2 1.5 0.0 F
Aulacomnium palustre (Hedw.) Schwägr. 2 1.0 0.5 A
Bartramia pomiformis Hedw. 10 2.5 0.4 ACFM
Brachythecium oxycladon (Brid.) A. Jaeger 10 3.4 2.0 ACF
B. plumosum (Hedw.) Schimp. 2 1.0 0.5 F
B. rivulare Schimp. 3 2.0 1.3 AF
B. rutabulum (Hedw.)Schimp. 2 1.5 0.0 F
B. salebrosum (Hoffm.) Schimp. 5 1.2 0.6 AF
B. velutinum (Hedw.) Schimp. 6 1.0 0.0 ACF
Brotherella recurvans (Michx.) M. Fleisch. 3 1.6 0.0 CM
Bryhnia graminicolor (Brid.) Grout 10 2.4 0.1 ACF
Bryoerythrophyllum recurvirostrum (Hedw.) P.C. Chen 6 2.7 0.0 AF
Bryum caespiticium Hedw. 3 1.7 0.3 A
B. flaccidum Brid. 7 2.4 0.0 ACF
B. lisae var cuspidatum (Bruch. & Schimp.) Margad. 3 1.3 0.0 AF
B. pseudotriquetrum (Hedw.) P. Gaertn. 9 2.3 0.0 ACFM
Callicladium haldanianum (Grev.) H.A. Crum 2 1.0 0.0 F
Campylium chrysophyllum (Brid.) Lange 12 2.5 0.5 ACF
C. hispidulum (Brid.) Mitt. 2 1.0 0.0 AF
Ceratodon purpureus (Hedw.) Brid. 4 1.5 0.0 AM
Conardia compactaS1 (Müll. Hal.) H. Rob. 2 1.5 0.0 F
Cratoneuron filicinum (Hedw.) Spruce 6 2.0 0.7 AF
Dichodontium pellucidum (Hedw.) Schimp. 3 1.3 0.0 AF
Dicranella heteromalla (Hedw.) Schimp. 5 1.6 0.4 CF
D. varia (Hedw.) Schimp. 3 2.3 0.0 F
Dicranum fulvum Hook. 15 3.6 2.2 ACFM
D. montanum Hedw. 13 2.7 0.2 ACM
D. scoparium Hedw. 5 2.2 0.3 ACM
Didymodon rigidulus Hedw. 5 1.8 0.4 AF
D. ferrugineusS1/S2 (Schimp.) M.O. Hill 2 1.0 0.0 F
Diphyscium foliosum (Hedw.) D. Mohr 7 1.3 0.0 ACM
Encalypta procera Bruch 7 3.3 0.7 AF
Eurhynchium hians (Hedw.) Sande Lac. 2 3.0 0.0 F
Fabronia ciliarisS1 (Brid.) Brid. 2 1.0 0.0 AF
Fissidens adianthoides Hedw. 3 1.3 0.3 F
F. bryoides Hedw. 9 3.3 0.0 AF
F. dubius P. Beauv. 9 2.0 0.2 ACFM
F. taxifolius Hedw. 5 2.2 0.0 F
82 Northeastern Naturalist Vol. 16, No. 1
No. Average Average
Species sites frequency dominance R
Gymnostomum aeruginosum Sm. 8 3.3 1.6 ACF
Hedwigia ciliata (Hedw.) P. Beauv. 4 1.7 0.2 ACM
Herzogiella striatella (Brid.) Z. Iwats. 2 2.0 0.5 CM
Homalia trichomanoides (Hedw.) Schimp. 3 1.3 0.0 C
Homomallium adnatum (Hedw.) Broth. 5 1.4 0.0 ACF
Hygroamblystegium tenax (Hedw.) Jenn. 8 1.8 0.8 AF
Hygrohypnum luridum (Hedw.) Jenn. 2 1.0 0.5 F
Hymenostylium recurvirostrum (Hedw.) Dixon 6 2.8 1.8 AF
Hypnum cupressiforme Hedw. 4 3.0 3.0 AM
H. imponens Hedw. 4 2.3 1.0 CM
Isopterygiopsis muelleriana (Schimp.) Z. Iwats. 5 1.8 0.2 CF
Leskeella nervosa (Brid.) Loeske 2 1.0 0.0 A
Leucobryum glaucum (Hedw.) Ångström 8 2.7 0.0 ACFM
Mnium marginatum (Dicks.) P. Beauv. 10 2.8 0.4 AF
M. thomsonii Schimp. 3 1.0 0.0 F
Myurella julaceaS2 (Schwägr.) Schimp. 2 1.0 0.0 A
M. sibirica (Müll. Hal.) Reimers 10 2.8 0.0 AF
Orthotrichum anomalum Hedw. 3 2.0 0.0 A
Oxystegus tenuirostris (Hook. & Taylor) A.J.E. Sm. 9 1.9 0.0 ACFM
Paraleucobryum longifolium (Ehrh.) Loeske 5 1.8 0.2 CM
Philonotis fontana (Hedw.) Brid. 3 1.3 0.7 A
P. marchica (Hedw.) Brid. 3 2.0 0.0 ACF
Plagiomnium ciliare (Müll. Hal.) T.J. Kop. 2 2.5 0.0 F
P. cuspidatum (Hedw.) T.J. Kop. 10 2.1 0.2 ACF
P. rostratum (Schrad.) T.J. Kop. 6 2.8 0.5 F
Plagiopus oederiana (Brid.) Limpr. 4 2.0 0.8 AF
Plagiothecium cavifolium (Brid.) Z. Iwats. 12 3.5 1.1 ACF
P. denticulatum (Hedw.) Schimp. 4 1.8 0.0 AC
P. laetum Schimp. 7 1.8 0.3 ACM
Platydictya confervoides (Brid.) H.A. Crum 3 2.7 0.0 AF
P. jungermannioidesS2 (Brid.) H.A. Crum 3 2.0 0.0 AF
Platygyrium repens (Brid.) Schimp. 6 1.5 0.0 AC
Platyhypnidium riparioides (Hedw.) Dixon 3 1.0 0.0 F
Pohlia cruda (Hedw.) Lindb. 5 2.8 0.0 ACFM
P. nutans (Hedw.) Lindb. 10 3.8 0.4 ACFM
Polytrichastrum alpinum (Hedw.) G.L. Sm. 6 3.0 0.7 ACM
Polytrichum pallidisetum Funck 3 1.0 0.0 AC
Pseudotaxiphyllum distichaceumS2/S3 (Mitt.) Z. Iwats. 4 2.0 0.3 AC
P. elegans (Brid.) Z. Iwats. 13 3.7 0.6 ACFM
Pterigynandrum filiforme Hedw. 4 1.8 0.3 AC
Pylaisiadelpha tenuirostris (Bruch & Schimp.) W.R. Buck 6 2.0 0.3 AC
Racomitrium heterostichum Cardot 5 1.8 0.8 AC
Rhabdoweisia crispata (Dicks.) Lindb. 5 2.8 1.5 CM
Rhizomnium punctatum (Hedw.) T.J. Kop. 2 1.0 0.0 F
Rhodobryum ontariense (Kindb.) Paris 2 1.0 0.0 AF
Rosulabryum capillare (Hedw.) J.R. Spence 5 2.6 0.0 AC
Schistdium apocarpum (Hedw.) Bruch & Schimp. 9 2.0 0.3 ACFM
S. lancilifolium (Kindb.) H.H. Blom 3 2.3 0.3 CF
Steerecleus serrulatus (Hedw.) H. Rob. 4 1.7 0.0 FM
Taxiphyllum deplanatum (Schimp.) M. Fleisch. 3 1.0 0.0 F
Tetraphis pellucida Hedw. 4 1.0 0.0 CM
Thuidium delicatulum (Hedw.) Schimp. 13 1.4 0.4 ACFM
Tortella tortuosa (Hedw.) Limpr. 9 2.2 0.8 ACF
Tortula mucronifolia Schwägr. 2 1.0 0.0 F
Ulota hutchinsiae (Sm.) Hammar 6 2.0 0.2 ACM
2009 N.L. Cleavitt, S.A. Williams, and N.G. Slack 83
No. Average Average
Species sites frequency dominance R
Liverworts
Anastrophyllum michauxii (F. Weber) H. Buch. 3 1.3 0.0 ACM
A. minutum (Schreb.) R.M. Schust. 6 1.3 0.0 ACM
Barbilophozia attenuata (Nees) Loeske 6 1.8 0.3 ACM
Bazzania denudata (Torr.) Trevis. 3 2.0 0.0 C
B. trilobata (L.) Gray. 6 2.3 0.7 CFM
Blepharostoma trichophyllum (L.) Dumort. 3 1.3 0.0 AC
Calypogeia fissa (L.) Raddi 2 1.5 0.0 C
C. muelleriana (Schiffner) K. Müller 2 1.0 0.0 AC
Cephaloziella rubella (Nees) Warnst. 7 1.9 0.0 ACF
C. stellulifera (Taylor) Schiffner 2 1.0 0.0 F
Cololejeunea biddlecomiae (Austin) A. Evans 5 1.8 0.0 ACF
Conocephalum conicum (L.) Underw. 7 2.1 1.1 AF
Diplophyllum apiculatum (A. Evans) Stephani 5 2.4 0.3 CFM
Frullania eboracensis Gottsche 4 1.5 0.0 AC
Jamesoniella autumnalis (DC.) Stephani 10 2.3 0.1 ACFM
Lejeunea cavifolia (Ehrh.) Lindb. 6 1.2 0.0 CF
Lepidozia reptans (L.) Dumort 5 1.4 0.0 CM
Lophocolea heterophylla (Schrad.) Dumort. 4 1.5 0.0 CFM
L. minor Nees 2 2.0 0.0 A
Lophozia ventricosa (Dicks.) Dumort. 5 2.2 0.0 ACM
Marchantia polymorpha L. 2 1.0 0.0 F
Marsupella emarginata (Ehrh.) Dumort. 2 2.5 1.0 AM
Metzgeria conjugata Lindb. 6 2.2 0.5 CF
M. furcata (L.) Corda 2 1.5 0.0 C
Plagiochila asplenioides (L.) Dumort. 7 1.4 0.3 CFM
Porella platyphylla (L.) Pfeiff. 5 1.4 0.3 ACM
Preissia quadrata (Scop.) Nees 4 2.3 0.5 F
Ptilidium pulcherrimum (Weber) Hampe 9 2.1 0.0 ACM
Radula complanata (L.) Dumort. 8 2.1 0.0 ACFM
R. tenax Lindb. 3 2.0 0.0 C
Reboulia hemisphaerica (L.) Raddi 3 1.7 0.0 AF
Scapania mucronata H. Buch. 3 2.3 0.0 A
S. nemorea (L.) Grolle 12 3.7 1.0 ACFM
Tritomaria exsecta (Schmider) Schiffner 3 1.3 0.0 AC
T. exsectiformis (Breidl.) Schiffner 3 1.0 0.0 AC
Appendix B. List of the species not included in the ordination. a) Species that were found
at only one of the 19 sites surveyed in NY, and b) species that were found only at the ACAD
(Maine) sites. For NY, rare species are indicated by a superscript with their S-rank.
a) Species that were found at only one of the NY sites:
Mosses
Abietinella abietina (Hedw.) M. Fleisch.
Amblystegium riparium (Hedw.) Schimp.
Aulacomnium heterostichum (Hedw.) Bruch & Schimp.
Barbula unguiculata Hedw.
Brachythecium acuminatum (Hedw.) Austin
B. populeum (Hedw.) Schimp.
Bryhnia novae-angliae (Sull. & Lesq.) Grout
Campylium polygamum (Schimp.) C.O.E. Jensen
Coscinodon cribrosusS1 (Hedw.) Spruce
Cyrto-hypnum pygmaeumS2 (Schimp.) W.R. Buck & H.A. Crum
Ditrichum lineare (Sm.) Lindb.
84 Northeastern Naturalist Vol. 16, No. 1
Encalypta ciliata Hedw.
Fissidens subbasilaris Hedw.
Funaria hygrometrica Hedw.
Grimmia pilifera P. Beauv.
Hygroamblystegium fluviatile (Hedw.) Loeske
Loeskeobryum brevirostre (Brid.) M. Fleisch.
Hypnum lindbergii Mitt.
Leucodon andrewsianus (H.A. Crum & L.E. Anderson) W.D. Reese & L.E. Anderson
Mnium ambiguumS2 H. Müll.
M. spinulosum Bruch & Schimp.
M. stellare Reichard
Orthotrichum stellatum Brid.
O. strangulatum P. Beauv.
Pohlia annotina (Hedw.) Lindb.
Pohlia bulbifera (Warnst.) Warnst.
Racomitrium aciculare (Hedw.) Brid.
Schistidium rivulare (Brid.) Podp.
Schwetschkeopsis fabroniaS1 (Schwägr.) Broth.
Seligeria calcareaS1 (Hedw.) Bruch & Schimp.
S. donnianaS2 (Sm.) Müll. Hal.
Sematophyllum demissumS1 (Wilson) Mitt.
Taxiphyllum taxirameumS2 (Mitt.) M. Fleisch.
Thamnobryum subserratum (Hook.) Nog. & Z. Iwats.
Thuidium scitum (P. Beauv.) Austin
Timmia megapolitana Hedw.
Tortella fragilis (Hook. & Wilson) Limpr.
Tortula pagorumS1 (Milde) De Not.
Warnstorfia fluitans (Hedw.) Loeske
Weissia controversa Hedw.
Liverworts
Aneura pinguis (L.) Dumort. .
Bazzania tricrenata (Wahlenb.) Trevis.
Calypogeia neesiana (C. Massal. & Carestia) K. Müll.
Frullania tamarisci var. asagrayana (Mont) S. Hatt.
F. riparia Hampe
Herbertus aduncus subsp. tenuis (A. Evans) A.A. Mill. & E.B. Bohrer
Lophozia bicrenata (Schmidel) Dumort.
Porella pinnata L
Radula obconica Sull.
Scapania scandica (Arnell & H. Buch.) Macvicar
b) Species that were found only at the ACAD sites in Maine:
Mosses
Aulacomnium androgynum (Hedw.) Schwägr.
Hylocomium splendens (Hedw.) Schimp.
Hypnum plicatulum (Lindb.) A. Jaeger
Isothecium stoloniferum Brid.
Mnium hornum Hedw.
Racomitrium microcarpum (Hedw.) Brid.
Sphagnum compactum Lam. & DC.
Liverworts
Cephalozia lunulifolia (Dumort.) Dumort.
Gymnocolea inflata (Huds.) Dumort.
Lophozia longidens (Lindb.) Macoun
Nowellia curvifolia (Dicks.) Mitt.
Scapania undulata (L.) Dumort.