Wetland seed dispersal by white-tailed deer in a large freshwater wetland complex
Wetland seed dispersal by white-tailed deer in a large freshwater wetland complex
Kelley L. Flaherty 1
James S. Rentch 0
James T. Anderson 0
Associate Editor: Dennis F. Whigham
0 Division of Forestry and Natural Resources, West Virginia University , PO Box 6125, Morgantown, WV 26506-6125 , USA
1 College of Science, Technology and Math, Alderson Broaddus University , 1010 College Hill Drive, Philippi, WV 26416 , USA
Mechanisms of long-distance dispersal are important in establishing and maintaining plant populations in isolated wetland habitats. White-tailed deer (Odocoileus virginianus) have been cited as long-distance dispersers of both native and exotic plant species in North America; however, knowledge regarding their influence in wetlands is limited. Given traditional classification methods for seed dispersal, white-tailed deer are not likely viewed as important dispersal mechanism for wetland plants. We collected naturally deposited white-tailed deer faecal pellet piles from wetlands in Canaan Valley, West Virginia, USA. Pellet piles were cold-stratified and germinated seedlings over a layer of sterile potting mix. The percentage of germinated seedlings with a facultative wetland (FACW) or obligate wetland (OBL) plant indicator status were compared to the frequency of occurrence to those of germinated plants with facultative upland (FACU) or upland (UPL) indicator status. We identified 38 species. Of these, 1 % were UPL, 38 % were FACU, 18 % were FACW and 21 % were OBL. Graminoid species accounted for 42 %; forbs and woody species accounted for 29 % each. Our research has suggested that endozoochory by herbivores contributes to long-distance dispersal of wetland plants.
Appalachians; endozoochory; Juncus effusus; Odocoileus virginianus; Oxalis dillenii; West Virginia; wetland plants
Much of the research concerning the effects of deer on
plant communities have focused on their role as
browsers and the potential for overbrowsing
Waller 1997; Stromayer and Warren 1997; Royo et al.
. However, several studies have looked at the role
of white-tailed deer as both seed predators and seed
(Cambell and Gibson 2001; Vellend et al. 2003;
Furedi and McGraw 2004; Myers et al. 2004; Bartuszevige
and Endress 2008)
. Due to their large home-range size
(e.g. 66–235 ha in WV; Campbell et al. 2004)
potential to retain material in the digestive tract for
three or more days
(Mautz and Petrides 1971; Moussie
et al. 2005)
, white-tailed deer have the potential to
carry seeds great distances (Janzen 1984). Vellend et al.
(2003) suggested that this would result in 95 % of
germinable seeds being deposited >100 m from the parent
plant and 30 % deposited >1 km from the parent plant.
This may have a considerable effect on metapopulation
initiation, growth and gene flow of irregularly distributed
and rare plant species
(Myers et al. 2004)
Myers et al. (2004) found that 72 species of forest
and old-field plants germinated from faecal pellet
samples with a mean of 38 germinations per pellet group.
The germinated seeds ranged from forbs to tree
species. In contrast,
Cambell and Gibson (2001)
two species germinated from 22 pellet group samples.
Although deer may play an important role in the
dispersal of seed for many plants, they may also play a role in
the spread of exotic species
(Cambell and Gibson 2001;
Bartuszevige and Endress 2008; Williams et al. 2008)
Traditional methods of determining dispersal
mechanism are to classify plants based on seed
characteristics. However, seeds of many species do not have special
characteristics and some may have more than one
(Drezner et al. 2001)
. Also, though a seed
may be physically adapted for one type of dispersal, it is
not known whether or not that seed could still germinate
if consumed by an herbivore. Drezner et al. (2001)
discussed the methods of seed dispersal of riparian plants
and argued that obligate wetland plants are more often
dispersed by water or wind while upland plants are more
often dispersed by animals. This study evaluated few
obligate or facultative wetland plants (n = 10) and many
upland or facultative upland plants (n = 46).
Obligate or facultative wetland plants with highest
fitness would disperse via methods that would ensure
that seeds are deposited in favourable growing
conditions. Thus, many wetland plants may not be adapted
to long-distance seed dispersal by large ungulate
herbivores such as white-tailed deer and are thus consumed
rather than carried by deer. We examined the
potential for white-tailed deer to disperse wetland species by
collecting and germinating seeds from natural faecal
pellet piles from the Canaan Valley, West Virginia, USA
high-elevation wetland complex to determine the
species of germinable seeds they contain as well as what
percentage come from obligate and facultative wetland
Canaan Valley, located in Tucker County, West Virginia,
USA is the highest elevation valley east of the Rocky
. As such, the climate and,
accordingly, the vegetation of the valley are more similar
to northern boreal forests than to the deciduous forests
of surrounding West Virginia. Once home to large stands
of red spruce (Picea rubens), intense logging followed
by fires drastically changed the soils and vegetation of
the valley to their present condition
valley floor averages 975 m above sea level. This,
coupled with surrounding mountains which rise 150–240
m above the valley, creates a relatively cool, moist
climate and a short growing season of ~90 days
. The average annual precipitation is 137 cm and
annual snowfall is 305 cm
characteristics set this area apart from low-elevation wetland
and upland areas in the surrounding counties.
Canaan Valley encompasses ~176 km2 (17 600 ha)
of land. Approximately 20 % of the land area is made
up of various wetland community types and another
23 % is northern hardwood forest
all the high-elevation wetlands in West Virginia, Canaan
Valley is home to the largest contiguous wetland
(3000 ha; Byers et al. 2007)
. This wetland
complex is home to 27 distinct wetland community types
ranging from quaking aspen (Populus tremuloides)
groves to sphagnum (Sphagnum spp.) and polytrichum
(Polytrichum spp.) bogs and includes many rare wetland
(Fortney et al. 2015)
Canaan Valley is home to Canaan Valley State Park
(2433 ha) and the Canaan Valley National Wildlife Refuge
(6729 ha) and, at the time of this study, land owned by
the Canaan Valley Institute (1298 ha), a non-profit
organization. Sampling took place on a combination of
these three public access properties in the valley.
We collected fresh white-tailed deer faecal pellet groups
twice monthly from May to December 2005 and 2006 in
wetland habitats. In 2005, we collected pellet piles from
along three 300 m transects through both herbaceous,
shrub and forested wetlands within the Canaan Valley
National Wildlife Refuge and Canaan Valley State Park.
In 2006, six additional wetland transects were added
for a total of nine transects at sampling locations within
the refuge and state park
. We located
transect near known deer tails to increase the
opportunities to collect fresh samples. We collected piles by
walking along transects and selecting fresh pellet piles
from those within view. We chose piles that were visibly
moist and dark in colour. All visible pellets were removed
from surrounding vegetation and placed in plastic bags.
We did not observe any obvious fallen seeds on pellet
piles. We attempted to collect pellets without including
surrounding debris, including seeds that may have come
from the surrounding vegetation rather than through
endozoochory. Samples were then stored in sealed
plastic bags and refrigerated at 4 °C to retard
germination and fungal growth.
Individual pellets were broken by rinsing
gently through a 0.5-mm sieve. The resulting seeds and
residual matter were stored in Petri dishes at 4 °C for
a period of 3 months to simulate overwintering
et al. 2004)
. In March, the seeds were spread on top of
a layer of sterile growing medium in 10 cm diameter
planting pots and kept moist and were subsequently
housed in a greenhouse and watered when needed. The
pots were kept in greenhouse conditions until
germination and identification of species germinated was
possible. The number of each plant species that germinated
from each pellet group was recorded.
We determined the wetland indicator status of all plants
germinated from pellet piles. For the purposes of our
analysis, we pooled the species that had OBL (obligate
wetland: plants with >99 % frequency of occurrence in
wetlands) or FACW
(facultative wetland: plants with
67–99 % frequency of occurrence in wetlands; Lichvar
et al. 2014)
status as these plants are most likely to be
adapted for growth and dispersal in wetlands. We used
wetland indicator status values for Eastern Mountains
and Piedmont region as listed in the U.S. Army Corps
of Engineers National Wetland Plant List
(Lichvar et al.
. We excluded species that were considered
facultative (facultative: FAC; plants that are equally likely to be
found in uplands and wetlands), species with an unknown
status and species that were only identified to the genus
level. We also classified each species as graminoid, forb
or woody species (including trees and shrubs). We used
a chi-square test to compare the proportion of species
germinated that were either UPL (upland: plants with
<1 % frequency of occurrence in wetlands) or FACU
(facultative upland: plants with 1–33 % frequency of
occurrence in wetlands) with those that were either FACW or
OBL. We considered differences at the P < 0.05 level to be
significant. We defined the frequency of occurrence as
the number of pellet piles in which each species occurred
out of the number of total germinated pellet piles. We
defined abundance as the total number of seedlings
present in all samples. We also compared the frequency of
germination events that were either UPL or FACU with
those that were either FACW or OBL. We repeated these
tests for the proportion and frequency of germination of
plants that were graminoid, forbs or woody. Finally, we
compared the frequency of native and exotic plants
germinating in the pellet piles.
We collected 55 pellet piles in 2005 and 160 pellet piles
in 2006. Of those collected in 2005, 45 % of the pellet
piles planted germinated at least one species resulting
in a total of 14 species (Table 1). Of those collected in
2006, 38 % of the pellet piles germinated at least one
species resulting in 31 species germinating (Table 1).
Thirty-eight species were identified over a period of
2 years (two additional seedlings were identified to the
We found no significant difference between the
proportion of species germinated that have a FACW (n = 8)
or OBL (n = 9) wetland indicator status (40 %) and those
that had a FACU (n = 12, 35 %) or UPL (n = 1) status
(35 %, P > 0.05; Table 2). There was also no difference
in the combined frequency of FACW and OBL (38 %)
plants versus FACU plants and UPL (n = 1) plants (35 %,
P > 0.05; Table 2). The combined abundance of seedlings
that were FACU or UPL (57 %; Table 2) was significantly
more than the combined proportion of FACW (13 %) and
OBL (17 %) stems counted (χ2 = 22.222, df = 1, P < 0.001;
Both the proportion of forb species (n = 11, 29 %)
and woody species (n = 11, 29 %) that germinated from
pellet piles were less than the proportion of graminoid
species (n = 16, 42 %) that germinated; however, the
difference was not significant (P > 0.05). The frequency of
both graminoids (n = 44, 45 %) and forbs (n = 36, 37 %)
was significantly higher than for woody species (n = 17,
18 %, χ2 = 11.9, df = 2, P < 0.01; Table 2). The
abundance of individual seedlings that were forbs (42 %) and
graminoids (48 %) were significantly greater than the
abundance of woody seedlings (10 %, χ2 = 56.1, df = 2,
P < 0.001; Table 2), but the abundance of graminoids and
forbs did not significantly differ (P > 0.05).
Lastly, we found the frequency of exotic seedlings
(n = 15, 13 %) was significantly lower than the frequency
of native seedlings germinating (n = 97, 87 %, χ2 = 60.03,
df = 1, P < 0.001; Table 2). The abundance of exotic
seedlings (n = 35, 15 %) was significantly lower than the
frequency of native seedlings germinating (n = 202, 85 %,
χ2 = 117.68, df = 1, P < 0.001; Table 2).
We observed no difference in the proportion of wetland
and upland plant species germinating in pellet piles
collected. However, there were a significantly higher
abundance of UPL and FACU seedlings germinating. While a
difference in frequency of plants seems to agree with
the hypothesis that upland plants may be more prone
to dispersal by white-tailed deer than wetland plants,
there was no difference in the proportion of wetland and
upland species. The difference in frequency could be
attributed to the successful germination of several FACU
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© The Author(s) 2017
the most abundant species being sweet vernal grass
A high proportion of germinated species were
graminoids. Although there was no significant difference
between number of species that were graminoids, forbs
or woody species, there was a significantly higher
frequency and abundance of graminoid seedlings than
woody seedlings. Endozoochory by large mammals is
often associated with the co-evolution of fleshy fruits
(Willson 1993; Beck and Vander Wall 2010)
Janzen (1984) suggested that the foliage of forbs and
grasses may attract herbivores to disperse small seeds.
While fleshy fruit may attract seed dispersers, the
mastication process may destroy larger seeds. Small,
rounded, hard seeds may support passage through the
digestive tract of ungulates better than larger seeds
(Moussie et al. 2005; Iravani et al. 2011)
. Our results
support this ‘foliage as fruit’ hypothesis (Janzen 1984) and
suggest that graminoids may be more likely to be
dispersed by herbivores that their traditional methods of
Successful dispersal and subsequent establishment
of graminoid species by deer may help to maintain or
expand herbaceous openings at both wetland and
upland sites. Large areas of Canaan Valley consist of wet
meadow habitat. White-tailed deer may help to
maintain these meadows, not only by reducing the growth
of woody species through browse, but also by
dispersing the seeds of graminoid species
Endress 2008; Iravani et al. 2011)
. Many studies have
examined the influence of white-tailed deer on upland
forest habitat. They are thought to affect the
regeneration of forest species through the overbrowsing of
(Rooney 2009; Griscom et al. 2011; Tanentzap
et al. 2012)
but may also alter the ground cover through
trampling, soil exposure or disturbance of leaf litter
(Knight et al. 2009). As dispersers of graminoid species,
deer also may reduce the capacity for woody species
regeneration by increasing the prevalence of grass
species within the ground cover in both upland and wetland
A key question raised by the results of this study is to
what degree these data are representative of the
species present in the Canaan Valley ecosystem that are
germinable when passed through the digestive system
of white-tailed deer and what percentage of the total
seeds consumed remain intact for each species. Of
those species recorded in Canaan Valley, 20 % are
obligate wetland species (OBL), 18 % are facultative wetland
plants, such as Oxalis dillenii, which occurred in 11 pellet
piles collected in 2006.
Although we did observe the presence of FACW and
OBL wetland species germinating in pellet piles, these
observations may underestimate the actual presence
of germinable wetland species in pellet piles. All pellet
piles were grown in moistened but not saturated soil.
Alternate conditions may be required to germinate all
wetland species present in a sample. Saturated
conditions would be present for at least some of the pellet
piles deposited naturally by white-tailed deer. Future
studies should simulate these saturated conditions.
Our study shows that some wetland plants can be
successfully dispersed by white-tailed deer. As they have
relatively large home ranges compared to other
, deer have the potential to
disperse seeds of wetland species between isolated
wetland patches. As dispersers, white-tailed deer could play
a role in maintaining or enhancing metapopulations of
wetland plants patchily distributed in an upland matrix
(Vellend et al. 2003)
. Maintenance of metapopulations
may also enhance overall plant species diversity within
a wetland complex. However, white-tailed deer may
also impact wetland restoration by successfully
dispersing seeds of some exotic species
(Vellend 2002; Myers
et al. 2004; Bartuszevige and Endress 2008)
. We found
seven exotic species germinated in our pellet piles, with
species (FACW), 15 % are facultative species (FAC), 24 %
are facultative upland species (FACU) and only 3 % are
upland species (UPL). We believe the abundance and
frequency of seeds in pellet piles are likely not a good
indicator of the proportions of these plants in the diet of
white-tailed deer and should not be used as an indicator
of such. Additionally, of those plants eaten, some may
not have germinated under the conditions provided.
We recorded the presence of species at our study sites
that have been reported by others as having germinated
from deer pellet piles but did not occur in our samples
(e.g. Achillea millefolium and Festuca ovina; Myers et al.
2004; Iravani et al. 2011)
. In the future, we suggest the
division of samples to allow the application of different
treatments that could promote the germination of
different species. All studies that we are aware of concerning
the germination of plant species from pellet piles have
been conducted under highly controlled conditions. It
remains to be seen, however, if these results translate
to pellet piles that germinate under more natural
conditions. Although, we sampled only from wetland sites,
herbivores may carry wetland seeds to upland
habitat not suitable for germination. Future studies should
examine the potential for seed loss through dispersal to
Sources of Funding
Funding for this project was provided by Canaan
Valley Institute, Regional Research Institute, and West
Virginia University Davis College of Agriculture, Natural
Resources and Design (McIntire–Stennis) (grant number
WVA00050). J.T.A. was supported by the National
Science Foundation under Cooperative Agreement
(OIA1458952) during manuscript preparation.
Contributions by the Authors
K.L.F. conceived of and conducted the experiment with
input from J.T.A. and J.S.R. Seedlings were identified by
K.L.F. with assistance from W. Grafton. K.L.F. wrote the
manuscript with input from J.T.A. and J.S.R.
Conflict of Interest
We thank the staff of Canaan Valley National Wildlife
Refuge and Canaan Valley State Park as well as field
assistants J. Harrell, G. Nesselrod and V. Richards for
assistance in the laboratory and greenhouse. We also
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thank W. Grafton for assistance in identifying seedlings.
This is scientific article number 3320 of the West Virginia
University Agricultural and Forestry Experiment Station.
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