Beach pinweed (Lechea maritima) COSEWIC assessment and status report: chapter 7
Habitat
In Canada, the species is strictly coastal, occurring on large and relatively stabilized barrier dune systems. It usually grows in open habitats on sandy substrates with little or no soil profile development, limited moisture and low nutrient content. The species is apparently unable to tolerate conditions on highly active dune sections. Most known populations occur on sites rarely or never subjected to overwash and offering some protection from the full intensity of onshore winds, salt spray and storm-related sand deposition. Typical locations include the landward slopes of foredunes, stable secondary dune crests, and dry interdune and backdune swales and plains. These habitats are often distinguished by the presence of low shrubs, especially beach-heather (Hudsonia tomentosa) and bearberry (Arctostaphylos uva-ursi), with these species often exceeding 40% cover while adjacent areas are more thoroughly dominated by the more disturbance-tolerant American beachgrass (Ammophila breviligulata). Fieldwork indicates that beach pinweed’s association with beach heather is particularly strong. In most populations, most plants were found growing with or near beach-heather, where the low shrub forms locally dominant and sometimes extensive patches. The herbaceous layer of beach pinweed sites is usually sparse, generally composed of American beachgrass with species such as sea-beach sedge (Carex silicea), shaved sedge (Carex tonsa), beach pea (Lathyrus japonicus), New-Belgium American aster (Symphyotrichum novi-belgii), Baltic rush (Juncus balticus) and seaside goldenrod (Solidago sempervirens), often with significant lichen cover.
Beach pinweed habitat differs on Portage and Fox Islands in New Brunswick’s Miramichi Bay. There, beach pinweed occurs in open woodland on old dunes well back from the shore and dominated by Jack pine (Pinus banksiana) and red pine (Pinus resinosa) with white pine (Pinus strobus), grey birch (Betula populifolia) and trembling aspen (Populus tremuloides) and with an understory of beach heather, bearberry and lichens. Populations on these sites are smaller than other New Brunswick sites, and the fact that plants are limited to the most open areas of forest suggests that this habitat may be suboptimal because of competitive exclusion mediated by partial shading by tree cover.
Evidence of competitive exclusion on open dunes was found on Hog Island, Prince Edward Island, where extensive areas are dominated by dense cover of broom-crowberry (Corema conradii) in combination with bearberry. These areas appear to be a more advanced successional stage of unusually old or stable dunes that is not found on other beach pinweed dunes. The beach pinweed associate beach-heather was restricted to the margins of occasional sandy blowouts in the broom-crowberry community and beach pinweed was entirely absent. There was also an apparent association between moderate levels of disturbance and greater seed germination at a few sites. A dune slack apparently subjected to a single storm surge event on Hog Island about two years prior to the site visit supported thousands of tiny but fertile pinweed plants, and the margins of an infrequently used ATV trail through open forested dune on Fox Island supported dozens of small plants. The ability of the small plants to survive in these areas and therefore their significance to the species’ persistence at the sites was not clear.
Coastal zones are dynamic environments, changing over time in location and in features, in response to long-term processes (e.g. isostatic adjustments, global water levels) (Forbes et al. 2006) and shorter term events (e.g. wave energy, storm surges). (O’Carroll et al. 2006). The current trends along the coast of the Northumberland Straight reflect the interaction of globally increasing water levels (due to ice melt and thermal expansion) and regional land subsidence (following the initial post-glacial rebound). Against this background of coastal retreat, there is potential for additional strong influences through the possible increase in the frequency of intense storms and the predicted reduction in the extent of winter ice formation, and its buffering function, during winter storms (Parkes et al. 2006).
The local expression of these complex processes is determined by the patterns of erosion, transport and deposition of sediment, as influenced by the local sediment budget, composition and height of the existing coastal features (e.g. cliffs, dunes), slope, orientation or exposure to wave action, fetch length and breaker-zone width, extent of shoreline structures or hardening of the shore, and nature of adjacent marine environment (e.g. water depth, currents) (O’Carroll et al 2006). In the case of dune systems, the outcome of the interaction of erosion and deposition may take several forms: landward migration of the dune, breaching or infilling, over-wash, destruction followed by eventual reconstitution, overall reduction or disappearance, or reshaping with parts of the dune appearing to grow while other parts are reduced (O’Carroll et al. 2006).
Recent increases in the frequency of severe storm events, potentially associated with human-caused climate change, have had an impact on coastal dunes supporting Canadian populations of beach pinweed, causing increased extent of flooding, erosion and breaching (Environment Canada 2006). A study of the evolution of southeastern New Brunswick coastal habitats immediately south of the pinweed occurrences shows a net decrease in the total area of beaches and dunes from 1944 to 2001 (O’Carroll et al. 2006a). Severe storm events have led to the opening of breaches and have left certain heavily affected areas devoid of vegetation and with lower topography. About 25% of the northern Bouctouche population has been affected by recent overwash events, with some portion of that 25% already lost (D.M. Mazerolle, pers. obs.). Information is insufficient to assess impacts on other sites but many sections of the Kouchibouguac barrier system including the South Kouchibouguac, North Richibucto and South Richibucto dunes have been notably modified in recent years (D.M. Mazerolle, pers. obs.).
Beach pinweed habitat at most other sites beyond those mentioned above has probably not yet had extensive storm impacts, because of higher elevations of foredunes. Thus climate change impacts are primarily a future threat to habitat. Future changes in climate and accelerated sea-level rise coupled with natural land subsidence are expected to exacerbate impacts on coastal habitats, increasing the likelihood of massive overwash and breaching and leading to destabilization and rapid landward dune migration (Shaw et al. 2001, O’Carroll et al. 2006a). Although habitat modification through storm disturbance is normal in coastal environments such as barrier dunes, a rise in the frequency and severity of disturbance could tend to change current pinweed habitat into much less suitable American Beachgrass-dominated dune or to bare sand. This issue is discussed in greater detail under Limiting Factors and Threats.
Aside from the above-mentioned storm effects, change in habitat quantity and quality in occupied sites has likely been relatively minor within the last three pinweed generations (estimated to equal 24-30 years). Succession could be causing declines in the Fox and Portage Island sites, the only ones where pinweed occurs under tree cover. Local residents indicate that Portage Island has become substantially more wooded over the past 40 years and the same situation likely applies to Fox Island. Populations at these sites are relatively low and could be lost over time.
New Brunswick and Prince Edward Island have seen a considerable increase in development within coastal areas during the late twentieth century (NBDELG 2002, Prince Edward Island DAF 2003), resulting in habitat loss and fragmentation (Stewart et al. 2003). During fieldwork, numerous areas of potential habitat were found to have been impacted by construction of roads, houses, cottages, boardwalks and access ramps. This has, however, had minimal direct impact on known pinweed sites, and current land management and development guidelines will likely limit future direct impacts of development.
Coastline modification, where it hardens shorelines or alters currents, can have an indirect effect on pinweed habitat by impeding the longshore transport of sand, potentially creating a negative sediment budget for beaches and dunes (Stewart et al. 2003), which could be especially significant under conditions of rapidly rising sea-levels. Additionally, development can bring a rise in pedestrian traffic and recreational activities such as all-terrain vehicle (ATV) use. Beach pinweed habitat at South Richibucto Dune has been noticeably altered by vehicle traffic, with several well-worn vehicle tracks passing through pinweed patches, eliminating vegetation in certain areas and causing blowouts. Several other populations (especially those on the Bouctouche Dune and in Kouchibouguac and Prince Edward Island National Parks) are situated in prime summer recreational areas and minor trampling impacts were found at the former two sites.
Five populations occur on federal land. In New Brunswick, the South Kouchibouguac Dune and North Richibucto Dune sites are situated within Kouchibouguac National Park and the Portage Island occurrence is within the Portage Island National Wildlife Area. In Prince Edward Island, the Blooming Point population is within Prince Edward Island National Park and the two Hog Island populations are on federal land held in trust for the Lennox Island First Nation.
The two Bouctouche Dune populations are on private land owned by the forestry company J.D. Irving Ltd. This 10 km sand spit is presently identified under J.D. Irving’s Unique Areas Program and is the site of an interpretive centre focusing on coastal ecology and a 2 km dune boardwalk that has been open to the public since 1997. J.D. Irving retains the right to alter management of its Unique Areas sites, but as a very publicly visible site, protection of the Bouctouche Dune is unlikely to change through the foreseeable future.
The Cabot Beach Provincial Park population and most individuals in the two Conway Sandhills populations (with a minority possibly occurring on a small parcel of private land) are on Prince Edward Island provincially owned land. Prince Edward Island’s provincial parks are managed by the Department of Tourism, often with minimal consideration for biological diversity, but the dunes of Cabot Beach are also identified as a provincial Natural Area by the Department of Environment, Energy and Forestry under the Natural Areas Protection Act, and that designation prohibits activities detrimental to the dune.
The remaining populations, Fox Island, South Richibucto Dune and South Richibucto Island in New Brunswick and Cascumpec Sandhills in Prince Edward Island are on private land. All population sites, including those on private lands, are in theory afforded protection through provincial laws regulating development in coastal areas. The New Brunswick Trespass Act, administered by the Department of Justice, prohibits the driving of motorized vehicles and construction of roads on sand dunes, although enforcement of the act is difficult. The province’s recent Coastal Areas Protection Policy limits most development on dunes but allows the construction of structures that provide access and certain structures and habitations within an adjacent 30 m buffer zone. In Prince Edward Island, the Planning Act’s Subdivision Development Regulations, Section 40(1) state that “No person shall develop or construct a road on any primary, secondary, or baymouth barrier sand dunes.” All Prince Edward Island Lechea habitats are all barrier baymouth dunes and are therefore protected from development. Prince Edward Island’s Environmental Protection Act specifies that development adjacent to sand dunes requires an impact assessment and prohibits vehicular traffic that interferes with natural dune succession.
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