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SWEET PEPPERBUSH

Clethra alnifolia


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

Picture of Sweet pepperbush

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.