Beach pinweed (Lechea maritima) COSEWIC assessment and status report: chapter 9

Population Sizes and Trends

Search Effort

All known populations were visited by the authors between 2003 and 2006, although portions of several sites were not visited. An additional 25 potential sites were surveyed for the preparation of this report and through other AC CDC and Bouctouche Dune Irving Eco-Centre (IEC) fieldwork (Figure 3). Survey efforts to date have included a wide variety of dune habitats but have mainly focused on large stabilized dune systems along New Brunswick’s eastern coast and Prince Edward Island’s northern coast. In New Brunswick, search efforts have been extensive, addressing almost all potential habitat. Unsurveyed dunes in northeastern New Brunswick consist of less suitable narrow and relatively unstabilized barrier dunes. Available information can thus be considered to reliably represent the species’ distribution in the province. Although the larger and more stable dune systems on Prince Edward Island have been surveyed, many smaller dunes are unsurveyed and there remains a small chance that other occurrences will be found.

It has been suggested that the species could occur on the Magdalen Islands in Quebec, where coastal habitats have many similarities to those in Prince Edward Island and eastern New Brunswick. However, the Magdalens have been extensively surveyed by botanists. Nova Scotia offers a limited potential for additional beach pinweed occurrences. Dunes on the north coast of mainland Nova Scotia and elsewhere in the province are generally not as well developed as those in New Brunswick and Prince Edward Island and are therefore less suitable for the species. This is demonstrated by the fact that the species most closely associated with beach pinweed occurrence (beach heather - Hudsonia tomentosa) is limited in Nova Scotia to only two dune systems near Antigonish. No fieldwork was conducted on Nova Scotia dunes, but specimens of Lechea intermedia potentially from dunes in the major Nova Scotia herbaria were examined, and no specimens of L. maritima were found.


Abundance

The total known Canadian population of beach pinweed is estimated to be 181 000+ plants. This is a rough estimate and is likely somewhat conservative due to unsurveyed portions of suitable habitat adjacent to known sites and to difficulty finding every plant within the surveyed areas at the more extensive sites. Table 2 lists populations with population size estimates and details of first discovery and most recent observation. Population sizes in New Brunswick are highly variable, ranging from small scattered patches in the northern populations at Portage and Fox Islands to denser and much more extensive populations of tens of thousands in the Kouchibouguac and Richibucto dune system. The four population sites located there collectively comprise 65% of the population. Prince Edward Island population sizes are more consistent, with the exception of the large occurrence on Hog Island’s southern section, where an estimated 35,500 individuals were observed.


Fluctuations and Trends

Information gathered prior to 2003 is insufficiently detailed to determine if populations have undergone growth or decline. There is no literature evidence suggesting large fluctuations in Lechea maritima populations. The dense population (~20 000 estimated) of uniformly aged young plants apparently responding to a single disturbance event at the Hog Island South population, as well as similar observations in Lechea intermedia (C.S. Blaney, pers. obs.), do suggest that fluctuations could occur over multiple years. Aside from such localized events, it seems likely that the total population has been relatively stable over the past three generations (24-30 years). All five historic records (Portage Island, Fox Island, Kouchibouguac, South Richibucto and Bouctouche), discovered between 1892 and 1932, are now known to be extant, as is the 1984 record of P.M. Catling et al. from southern Hog Island. Where recent losses have been noted due to storm overwash, ATV use and trampling, effects to date are small and localized relative to the populations affected. Succession could be causing declines in the Fox and Portage Island sites, the only ones where pinweed occurs under tree cover. Early records from the sites do not indicate abundance but 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, especially at Fox Island where no plants were found in open habitats, could be lost over time. Search efforts between 2002 and 2006 have doubled the number of known populations and significantly increased the total number of individuals known to exist, but this likely represents a search effort effect rather than an actual population increase.

The potential for future decline is where concern arises, due to the effects of climate change-induced sea-level rise coupled with natural land subsidence and increased storm frequency and severity. Good information on projected long-term sea-level rise is available, but accounting for the future movement of dune habitats and thus estimating future population loss is not possible. Roughly 25% of the northern Bouctouche Dune occurrence has experienced recent overwash, with declines in plant density and local habitat loss observed within the affected zone. A large portion of the South Kouchibouguac, South Richibucto, North Richibucto and Bouctouche sites, representing 71% of the known population, are situated between 3 and 4 m elevation behind foredunes less than 5 to 6 m. Much of the remaining population is at similar elevations, though often behind higher dunes. This elevation range is presently affected only very rarely by storm events, but is projected to see the greatest increase in frequency of storm impacts. Sites at 3.1 m, 3.2 m and 3.3 m elevations are projected to be impacted by storm disturbance 4.5, 5.5 and 3.8 times more often by 2100 (Parkes et al. 2006). Field observations suggest that ideal beach pinweed habitat is flooded by storms very infrequently and it seems quite likely that the changes noted above could change beach heather–beach pinweed communities to American beachgrass-dominated or bare sand communities that are much less suitable for pinweed. Storm erosion effects are also not necessarily limited to those areas subjected to direct flooding, as erosion at lower elevations can destabilize the dune crests above and change their plant communities. A more detailed analysis of potential climate change effects is given below in Limiting Factors and Threats.

 

Table 2: Population size, area, and length of occurrence for each Canadian population of beach pinweed, with details of first and last observations
Site# Site name and province Pop. size AreaFootnote a, length of occurrence & notes First & most recent observations
1 Portage Island, NB 250-500 5 patches observed, one ~continuous over 0.15 km, others very small; scattered over 3 km. Note: Plants harder to find at this site in forest, likely more plants present though definitely uncommon First: Blake 1913;
Last: Blaney, et al. 2004
2 Fox Island, NB ~220 1 375 m2 observed occupied, discontinuous over 0.28 km + single point occurrence. Note: South 4.3 km of island, which may not support pinweed, was not surveyed First: J. Fowler 1892
Last: Blaney & Goltz 2005
3 South Kouchibouguac Dune, NB >50 000 280 000 m2 observed occupied, ~continuous over 4 km First: Blake 1913
Last: Mazerolle 2004
4 North Richibucto Dune, NB >50 000 210 900 m2, ~continuous over 7.5 km First: Mazerolle 2002
Last: Mazerolle 2004
5 South Richibucto Island, NB >10 000 125 000 m2 observed occupied, ~continuous over 1.3 km First: Blake 1913
Last: Mazerolle 2005
6 South Richibucto Dune, NB ~8 000 16 000 m2 observed occupied, ~continuous over 4 km First: Blake 1913
Last: Mazerolle 2004
7 Bouctouche Dune
(north section), NB
~5 000 55 000 m2 observed occupied, ~continuous over 1 km First: Marie-Victorin 1932 (N vs. S not specified); Last: Mazerolle 2004
8 Bouctouche Dune
(south section), NB
~5 000 110 000 m2 observed occupied, ~continuous over 3 km First: Mazerolle 2003
Last: Mazerolle 2004
9 Cascumpec Sandhills, PE ~250 Discontinuous over 0.06 km. Note: Northern 3.3 km of island, which may not support pinweed, was not surveyed First & Last: Blaney 2005
10 Conway Sandhills
(north section), PE
~5 000 Discontinuous over 4.9 km & ~continuous over 1.5 km. Note: A segment of 2.8 km, likely supporting pinweed, was not surveyed First: Blaney 2003
Last: Blaney & Curley 2005
11 Conway Sandhills
(south section), PE
>3 500 ~Continuous over 1.5 km First & Last: Mazerolle & Curley 2006
12 Hog Island (north section), PE ~740 Discontinuous over 1 km. Note: Northern 3.2 km of island, likely supporting pinweed, not surveyed First & Last: Blaney, Mazerolle & Curley 2006
13 Hog Island (south section), PE 35 500+ ~Continuous over 1.1 km + 0.7 km. Note: Population value includes very dense occurrence of young but reproductive plants; South 2 km of island, likely supporting pinweed, not surveyed First: P.M. Catling et al. 1984
Last: Blaney & Curley 2005
14 Cabot Beach Provincial Park, PE ~1 500 ~Continuous over 0.18 km + discontinuous over  0.16 km First: Vander Kloet 2005
Last: Blaney & Mazerolle 2006
15 Blooming Point, PE ~6 000 ~Continuous over 0.4 km First & Last:
Mazerolle 2006

Total estimated number of individuals: 181 000+

Site numbers correspond to those in Figure 3.


Rescue Effect

As a Canadian endemic, the Gulf of St. Lawrence variety (var. subcylindrica) of beach pinweed, can have no rescue from populations outside of Canada.

At the species level, rescue effect through the natural dispersal of plants from the United States is unlikely. The nearest occurrence of var. maritima is in south-central Maine, roughly 115 km from the Canadian border near St. Stephen, New Brunswick. Suitable dune habitat is very limited on the Bay of Fundy shore in New Brunswick, and with Fundy waters being much colder than the Gulf of St. Lawrence, a climatic limitation could exist. It is roughly 370 km from south-central Maine to the nearest area of the Gulf of St. Lawrence coast. While northern United States plants of var. maritima might be adapted to Gulf of St. Lawrence conditions and habitat is likely not limiting, such a dispersal event would probably be extremely infrequent.

Rescue effects between populations within the five regions of occurrence identified in Table 1 are plausible, with several populations separated only by marginal or unsuitable habitat on the scale of a few kilometres. As noted under Isolation and Fragmentation, there is a very limited chance for rescue effects between the five regions of occurrence.

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