Taxonomic group:
Plant, dicot
Family: Clethraceae, the White Alder
family
Growth Habit: Shrub
Status: Special Concern
Photo courtesy of Irene Wisheu, 2001.
Table of Contents
Description
Range and Distribution
Habitat
History
Biological Importance
Threats and Limiting
Factors
Protection
References
Description
Photo courtesy of William S. Justice.
The Sweet Pepperbush, Clethra alnifolia, is a tall
(1-2 meter), deciduous woody shrub. It has shiny, alternate, toothed leaves,
that are obovate-oblong in shape and have a short stalk (Gleason &
Cronquist, 1991). Its numerous small white flowers are borne on terminal
racemes and have a pleasant sweet-smelling fragrance (Taschereau, 1986).
Flowering occurs in the late summer, from mid-August through to mid-October
(Taschereau, 1986). During this period the shrub flowers prolifically;
however, for reasons not yet fully understood, viable seeds are rarely
produced (Newell, 2001). It follows that the Sweet Pepperbush populations
in Canada reproduce almost exclusively by vegetative means, namely vegetative
root-suckering (Newell, 2001). Sexual reproduction has been observed only
in one of the six Canadian populations, and even at this site - on Louis
Lake in Nova Scotia- seed production is infrequent (Hill et. al, 2000).
A lack of pollinating agents does not explain why the Sweet Pepperbush
has little successful sexual reproduction, as pollinators are abundant
while plants are in bloom at all six of the Canadian sites (Newell, 2001).
In the rare instances that seed production does occur, the shrub has dry
rounded capsular fruits that persist through winter (Gleason & Cronquist,
1991).
Range and Distribution
Adrienne Telford, 2001.
The Sweet Pepperbush's range is restricted to the coastal
plains of eastern North America, from Texas and Florida north to Maine
and disjunctly into Nova Scotia (Newell, 2001). As well, the shrub is
cultivated in Europe mainly for ornamental purposes (Taschereau, 1986).
Although the Sweet Pepperbush is quite common in the United States, in
Canada - the northernmost limit of its range - the situation is quite
the reverse. Its distribution is restricted to a geographically small
area on the southwestern tip of Nova Scotia. Here, it is found only along
the margins of six lakes, three of which were only recently discovered
(Hill et. al, 2000).
The restriction in the distribution of the Sweet Pepperbush
is without any obvious pattern (Wisheu et. al, 1994). Within the six locations,
extensive stands of Sweet Pepperbush are found on both Mill Lake and Mudflat
Lake in Annapolis County, while significant stands are found on Belliveau
Lake in Digby County, Louis Lake in Yarmouth County, and Pretty Mary Lake
in Annapolis County (Newell, 2001). Only one plant is found at Canoe Lake
in Yarmouth County (Newell, 2001).
The total population in Nova Scotia is extremely fragmented,
with approximately 75km separating the three newly discovered populations
in Annapolis County from the other sites (Newell, 2001). The absence of
viable seed production is possibly one of the reasons that this species
is so limited in its geographical distribution and in its number of occurrences
in Nova Scotia (Newell, 2001). Although only a total of six locations
are presently known, it is possible that Sweet Pepperbush populations
between the sites may yet be discovered (Newell, 2001).
Habitat
The Sweet Pepperbush is a main component of its wetland
community, and often forms the dominant shrub in its habitat (Newell,
2001). In Nova Scotia, it is found only along the immediate margins of
lakes, in open, un-shaded areas (Newell, 2001). The substrates of these
shoreline habitats are generally a coarse glacial till or granite, and
are relatively poor in nutrients (Keddy & Wisheu, 1989). The shrub
prefers shoreline areas that are somewhat protected from such wind-induced
disturbances as intense wave action, and zones that are essentially free
of ice scour disturbances (Hill et. al, 2000). The shrub occurs most often
on the western, northwestern, and southwestern sides of lakes (Newell,
2001). Furthermore, with the exception of Canoe Lake, the populations
occur on the shores of relatively small surface area, low catchment area
(under 2000 ha) lakes, characteristics that are associated with less intense
wind-induced disturbances (Hill et. al, 2000). Finally, the Sweet Pepperbush
is often found in association with other plant species including sweetgale
(Myrica gale), black huckleberry (Gaylussacia baccata),
northern bayberry (Myrica pensylvanica), winterberry (Illex
verticillata), and red maple (Acer rubrum) (Hill et.
al, 2000).
History
The Sweet Pepperbush was first discovered in Nova Scotia
in 1968 (Taschereau, 1986). In April 1986, it was designated threatened
by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).
At the time, there were reports of only three locations of Sweet Pepperbush
populations, one of which had only one plant. In May 2001, the Sweet Pepperbush's
status was downlisted to special concern in light of the discovery of
significant populations at three additional locations and the evidence
of seedling production (Newell, 2001).
Biological Importance
Sweet Pepperbush is biologically important as a representative
plant of the unique coastal plain floral element (Taschereau, 1986). Together
with the other members of this ecosystem, they provide important keys
to understanding the biological and climatic prehistory of the region,
as well as clues to the migration, adaptation, evolution, and survival
of flowering plants (Taschereau, 1986).
Threats and Limiting
Factors
Natural
The Sweet Pepperbush occurs in the Atlantic coastal plains
habitat of Nova Scotia, a habitat that is rare in its own right (Crins,
1997). This is one of many reasons behind its limited geographic distribution
and occurrences. Other natural limiting factors to Sweet Pepperbush populations
include its intolerance to shade and water level fluctuations, and its
infrequent seed production (Newell, 2001). The lack of sexual reproduction
in this plant reduces its ability to recover from any population loss
that may occur through alterations to its habitat (Newell, 2001). Furthermore,
the total Nova Scotian population is fragmented, and it is disjunct from
its main range in the eastern United States (Keddy & Wisheu, 1989).
Therefore, immigration among populations is unlikely, as is the rescue
potential for Nova Scotian populations (Newell, 2001). In other words,
should a Sweet Pepperbush population in Nova Scotia become extirpated,
there are no immediately adjacent populations that can help recolonize
(Keddy and Wisheu, 1989).
Private Lands
The most direct and immediate threat to Sweet Pepperbush
is cottage development. The shrub's shoreline habitat is unfortunately
considered an ideal location for real estate (Crins, 1997). It follows
that most of the Sweet Pepperbush populations occur on privately owned
land (Newell, 2001). Cottage development is currently putting pressure
on Sweet Pepperbush populations at Belliveau Lake, Mill Lake, Mud Flat
Lake, and Pretty Mary Lake, and is only expected to increase in the future
(Newell, 2001). Along with the direct impact of habitat loss from cottage
development, there are also associated secondary negative impacts. Cottage
development is often accompanied by the clearing of areas and the dumping
of sand along the shoreline for esthetic purposes (Newell, 2001). This
has a negative impact on Sweet Pepperbush populations as it creates gaps
in its distribution along the lakeshore (Newell, 2001). Another secondary
impact is the associated increase in recreational activity on
the lake margins that can be damaging to the shrub populations (Newell,
2001). Finally, as a shrub that is dependent on a relatively constant
water level, the human alteration and control of water levels in lakes,
such as through damming, can have a negative impact on the shrub's survival
(Newell, 2001).
Provincial Crown Lands
The populations on Louis Lake and Canoe Lake fall entirely
on Provincial Crown land, while on Pretty Mary Lake it is only a small
cove that is provincially owned (Newell, 2001). There are no obvious threats
to the Sweet Pepperbush populations on Provincial Crown land, however,
they are only afforded a weak protection under the Forest/Wildlife Guidelines
and Standards for Nova Scotia (Newell, 2001). Forestry activities have
occurred in the past near Louis Lake, and although the guidelines restrict
logging activity within 20 meters of the lake edge, they do not necessarily
prevent it (Newell, 2001).
Protection
As far as current legislation, the Sweet Pepperbush is
given only an extremely limited protection status in Nova Scotia, and
even then the protection is only afforded to those plants that fall on
Provincial Crown land (Newell, 2001). It is expected that once the new
provincial endangered species legislation is passed the Sweet Pepperbush
will be more aptly protected (Newell, 2001).
Recovery Efforts
A recovery plan is in the process of being developed (Newell,
2001) for the group of taxonomically unrelated species that make up the
unique coastal plains flora of southwestern Nova Scotia (Wisheu &
Keddy, 1994). The Atlantic Coastal Plain Recovery Team has compiled information
and validated existing data on the coastal plains plants, and has developed
an awareness program that includes public education campaigns on the conservation
of coastal plains plants (Newell, 2001). The Sweet Pepperbush is included
in this group as it shares a common habitat; however, as a shrub, the
Sweet Pepperbush is quite functionally different from the herbaceous species
that make up most of the coastal plains flora (Hill et. al, 2000). The
Sweet Pepperbush therefore has conservation needs that differ from the
other flora at risk (Hill et al, 2000). In particular, the Sweet Pepperbush's
species richness is greatest in lakes with low catchment areas, whereas
coastal plain herb species richness is tied to large catchment area lakes
(Hill et. al, 2001). There is a need to gather more information on lakes
of low catchment areas, as well as to assess and
accommodate the specific conservation needs of the Sweet Pepperbush (Hill
et. al, 2000).
References
Crins, W. 1997. Rare and endangered plants and their
habitats in Canada. Canadian Field-Naturalist 3: 506-517.
Gleason, H. A. and A. Cronquist. 1991. Manual of vascular
plants of northeastern United States and adjacent Canada, 2nd ed. New
York Botanical Garden, Bronx, New York 910p.
Hill, N. M., J. S. Boates, and M. F. Elderkin. 2000. Low
catchment area lakes:new records for rare coastal plain shrubs and Utricularia
species in Nova Scotia. Rhodora 102: 518-522.
Keddy, P. A. and I. C. Wisheu. 1989. Ecology, biogeography,
and conservation of coastal plain plants: some general principles from
the study of Nova Scotian wetlands. Rhodora 91: 72-94.
Newell, R. 2001. Update status report for Sweet Pepperbush,
Clethra alnifolia. Unpublished manuscript for COSEWIC, Ottawa, Canada.
Taschereau, P. 1986. Status report for Sweet Pepperbush,
Clethra alnifolia L. in Canada. Unpublished manuscript for COSEWIC, Ottawa,
Canada.
Wisheu, I. C. and P. A. Keddy. 1994. The low competitive
ability of Canada's Atlantic coastal plain shoreline flora: implications
for conservation. Biological Conservation: 68: 247-252.
Wisheu, I. C., C. J. Keddy, P. A. Keddy, and N. M. Hill.
1994. Disjunct Atlantic coastal plain species in Nova Scotia: distribution,
habitat and conservation priorities. Biological Conservation 68:
217-224.
Webpage by Adrienne Telford
Last Updated 12/5/01.
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