1Department of Biology, University of Central Missouri, Warrensburg, MO 64093.
2Botanical Research Institute of Texas, Fort Worth, TX 76102. 3The Field Museum,
Chicago, IL 60605. *Corresponding author - ely@ucmo.edu.
Vertical Distribution of Lichen Growth Forms in Tree
Canopies of Great Smoky Mountains National Park
Erin Fanning1, Joseph S. Ely1,2,*, H. Thorsten Lumbsch3,
and Harold W. Keller1,2
Abstract - Great Smoky Mountains National Park is an area known for its incredible
species diversity. This study was conducted in order to determine the vertical distribution
of lichen growth forms and overall lichen species richness on selected host-tree
species in the Park. Specifically, lichens were collected from Tilia americana var. heterophylla
(basswood), Abies fraseri (Fraser fir), Liquidambar styracifl ua (sweet gum),
and Fraxinus americana (white ash) at different canopy heights. A total of eight trees
(two for each species) were sampled using the double-rope climbing technique. Overall,
our results indicate that both host-tree species and canopy height infl uence lichen
species richness and distribution of growth forms. Three lichen species are reported as
candidates for new records in the Park: Gyalecta fl otowii Korber, Lecanora miculata
Ach., and Pyrenula pseudobufonia (Rehm) R.C. Harris.
Introduction
Lichens are an important component of many ecoregions (Brodo et al.
2001, Nash et al. 2002) and often comprise a large proportion of species
diversity. There are over 7700 species reported from North America, excluding
Mexico (Esslinger 2006). Some species of lichen have wide and
disjunct distributions, often showing the classical Asa Gray distribution
(Kurokawa 1972, Lumbsch 2004, Yoshimura 1968). There were 194 species
of corticolous lichens reported for Great Smoky Mountains National
Park (GSMNP) (Ciegler et al. 2003). Species of lichen form a vital part of
the canopy ecosystem and biodiversity in the Park. The aim of this study
was to explore corticolous lichen species richness and vertical distribution
of lichen growth forms (crustose, foliose, and fruticose) in the canopy
strata on selected host-tree species in GSMNP.
Methods
A safe and environmentally friendly method for accessing the tree
canopy involves the use of a double-rope climbing technique (Keller
2004). A climbing saddle, system of knots, and a double rope were used
to ascend the tree, enabling the climber to advance and reach heights of
more than 30 m to sample lichens. Samples were collected from all sides
83
The Great Smoky Mountains National Park All Taxa Biodiversity Inventory:
A Search for Species in Our Own Backyard
2007 Southeastern Naturalist Special Issue 1:83–88
84 Southeastern Naturalist Special Issue 1
of the tree (at 3 m elevational increments) on four different host species.
The minimum size of host trees was 42 cm in diameter at breast height.
A total of two sample bags (approximately 1000 cm3 each) were filled at
each height (Snell and Keller 2003). Host-tree species were Abies fraseri
(Pursh) Poiret. (Fraser fir), Fraxinus americana L. (white ash), Liquidambar
styraciflua L. (sweet gum), and Tilia americana L. var. heterophylla
(Vent.) Loud. (basswood). A total of eight trees were sampled from different
sites in the Park. Basswood was sampled from the Gabes Mountain
Trail and the West Prong Trail near the Tremont Institute. Fraser fir was
sampled from Clingman’s Dome, a high-elevation site. White ash was
sampled from the Cades Cove Loop Road and the Baxter Creek Trail.
Sweet gum was sampled from a sweet gum swamp along Cades Cove
Loop Road near the Visitor Center and a northwestern section of the Park
(Tritt Cemetery near Cosby). All sites were located in Tennessee and occurred
at low elevations, with the exception of Clingman’s Dome, which
is on the North Carolina/Tennessee border and is the highest point in the
park and Tennesse. Lichens were separated into three life-form categories
(crustose, foliose, and fruticose) and three height classes corresponding
to the lower (0–8.9 m), mid- (9–17.9 m), and upper (18–36 m) canopy
along the main trunk or bole of the tree. For the purpose of this study,
lichens surveyed include both those growing directly on bark and those
growing on corticolous bryophytes. Please note that the maximum height
of Fraser fir surveyed was in the mid-canopy, so there is no data for the
third height class. Lichen species richness (mean and standard error) for
each of the growth forms was calculated among sampled host-tree species
and respective heights. Voucher specimens of the new records are
deposited at the Field Museum in Chicago (F).
Results
Our survey resulted in the recording of seven orders, 18 families, and
68 species of lichens following Brodo et al. (2001) and Nash et al. (2002,
2004). Crustose lichens comprised six orders, 10 families, and 25 species,
while two orders, five families, and 12 species were fruticose. The foliose
lichens were the most species-rich group, including one order, five families,
and 31 species. Several orders and families included more than one growth
form. The following species of lichens identified in the course of this study
are candidates as new records for GSMNP: Gyalecta fl otowii Korber (ELY
5642), Lecanora miculata Ach. (ELY 5601), and Pyrenula pseudobufonia
(Rehm) R.C. Harris (LUMBSCH 19273c).
There were more foliose than crustose lichens at the mid-canopy on
Fraser fir and sweet gum, while there were no differences observed for
white ash (Figs. 1a, b). Lichen growth forms also varied by canopy height
across host species. There were more crustose lichens occurring in the
2007 E. Fanning, J.S. Ely, H.T. Lumbsch, and H.W. Keller 85
upper canopy on sweet gum than other host species (Fig. 1a). Foliose lichen
richness in the lower and mid-canopy was greater on Fraser fir than
either basswood or white ash (Fig. 1b). Mid-canopy crustose lichen richness
was higher on basswood than white ash (Fig. 1a). Foliose lichen
richness was highest on sweet gum than other host-tree species surveyed
(Fig. 1b). There were more fruticose lichens growing on sweet gum and
Figure 1. Mean
lichen species
richness and ±
1 standard error
bar of crustose
(a), foliose (b)
and fruticose (c)
growth forms
among hosttree
species (AF
= Abies fraseri
[Fraser fir], TH =
Tilia americana
var. heterophylla
[basswood], FA =
Fraxinus americana
[white ash],
and LS = Liquidambar
styracifl
ua [sweet gum])
and height (solid
line = 0–8.9 m,
dashed line =
9–17.9 m, and
dotted line = 18–
36 m). Please note
that Fraser’s fir
was only sampled
in the first two
height classes.
86 Southeastern Naturalist Special Issue 1
Fraser fir than on other host-tree species (Fig. 1c). There was only one species
of fruticose lichen that occurred on white ash and none occurred on
basswood (Fig. 1c). Overall, species richness was higher in crustose and
foliose lichens than in fruticose lichens (Figs. 1a–c).
Discussion
Our results indicate that host-tree species and canopy height infl uence
lichen species richness and growth forms. The foliose growth form had the
greatest species richness in comparison to the other growth forms. Other
studies have found similar patterns. For example, McCune et al. (2000)
showed that a significant relationship existed between lichen growth forms
and tree-canopy height in a forest canopy located in the state of Washington.
Fruticose lichens were less diverse than crustose and foliose lichens for all
height classes and tree species. A plausible explanation for this result may be
that fruticose lichens are typically found more along lateral branches, where
they receive more light than foliose lichens (Esseen et al. 1996). Because
our sampling was only from the trunk of the tree, our surveys are probably
not representative of the total fruticose species richness of the sampled trees
as a whole. There are obvious moisture and light gradients from the ground
to the upper canopy of forests that determine the distribution of lichen species.
Our results show that differences in the canopy had a significant effect
on the species richness on several species. Similar to what McCune et al.
(2000) found, there seems to be a pattern of lichen growth forms and species
richness to host species and canopy height. McCune et al. (2000) studied
the microhabitats of a Washington State conifer forest and observed that
substrates and tree canopy structure affected the distribution of lichens. In
particular, they showed that characters such as canopy height, living versus
nonliving trees, amount of cover, and trunk diameter were all factors that
displayed significant variation in epiphyte communities (McCune et al.
2000). Species richness was most markedly infl uenced by canopy height in
that forest system. Ellyson and Sillett (2003) showed similar results in that
the canopy height was the dominant gradient in the distribution of epiphytic
communities in a Sequoia sempervirens (Lamb. ex D. Don) Endl. (redwood)
old-growth forest. In a midwestern Quercus-Carya (oak-hickory) forest,
Peck et al. (2002) showed that there was a limited number of lichen species
(26%) that were generalists across host-tree species and habitats, and
the remaining species were more specific with respect to substrate, habitat,
and host-tree species. Furthermore, they found that the majority of species
encountered in the lower and mid-canopy were crustose and foliose lichens.
Results shown here have certain limitations. First, there is a limited number
of host-tree species sampled (n = 4) and also a limited number of individual
trees sampled per host species (n = 2). In addition, there were no microenvironmental
attributes (e.g., soil, slope, light) measured or recorded.
2007 E. Fanning, J.S. Ely, H.T. Lumbsch, and H.W. Keller 87
This preliminary study suggests that interesting patterns of lichen
stratification exist in the canopies of living trees. More data is needed from
additional individuals of each tree species to confirm trends noted here. In
addition, micro-environmental (light, moisture, temperature) and habitat
(aspect, slope, elevation) data need to be further investigated in order to
understand the processes associated with the patterns of lichen stratification
within GSMNP.
Acknowledgments
This study was financially supported in part by the National Science Foundation
DEB Award #0343447, Discover Life in America Award #2004-6, National Geographic
Society Committee for Research and Exploration Award #7272-02 to H.W.
Keller, Sigma Xi Grant-in-Aid of Research Award #3040094, and the University of
Central Missouri (UCM) McNair Scholars program to Erin Fanning. Special thanks
go to the UCM student climbers for their assistance in data collection (Cheryl Dunham,
Tommy Fayette, Amber Ferguson, and Ashley Willard). Charly Potorff and
Kenneth Snell were instructors for the rope-climbing techniques.
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