Dense Draba (Draba pycnosperma): COSEWIC assessment and status report 2022

Official title: COSEWIC Assessment and Status Report on the Dense Draba (Draba pycnosperma) in Canada

Committee on the status of Endangered Wildlife in Canada (COSEWIC)
Special concern 2022

COSEWIC assessment summary

Assessment summary – May 2022

Common name: Dense Draba

Scientific name: Draba pycnosperma

Status: Special Concern

Reason for designation: This small plant occurs on rock outcrops, cliffs, and talus slopes within 2.5 km of the coast along the Gaspé Peninsula and Strait of Belle Isle (Quebec, Newfoundland & Labrador), and is found nowhere else in the world. Fewer than 3000 plants are currently known, occupying a small portion of seemingly abundant suitable habitat. Invasive introduced plant species are degrading the draba’s habitat. As most plant colonies consist of only a few individuals and are associated with steep, dynamic substrates, they may be vulnerable to stochastic events such as rockslides. This species is near to qualifying for Threatened status, and failure to effectively mitigate the threats could result in the species becoming Threatened.

Occurrence: Quebec, Newfoundland and Labrador

Status history: Designated Special Concern in May 2022.

COSEWIC executive summary

Dense Draba
Draba pycnosperma

Wildlife species description and significance

Dense Draba is a small perennial plant that grows in dense clumps. Basal rosette leaves are covered with four-rayed cross-shaped hairs, which are sometimes spurred or branched. Flower stalks bear 5–40 white flowers and one to four leaves. The plump inflated dry fruits contain seeds that overlap in shingle-like fashion and that are turned obliquely to the thin wall dividing the two fruit cavities. It is endemic to eastern Canada.

Distribution

This species is limited to the Gaspé Peninsula region and along the north shore of the Gulf of St. Lawrence to Labrador, near the Québec border, with most of the population concentrated around Percé. An additional historical record exists from the island of Newfoundland. Past reports from Nova Scotia are now known to have been incorrect.

Habitat

This species grows in full sun or light shade on mesic to xeric sites, on escarpments, rocky sea cliffs, talus slopes, or rock outcrops at or near the seashore. The parent rock at these sites is composed of mudstone, limestone or calcareous sandstone, and conglomerate.

Biology

The species flowers from late May to July and the fruiting season lasts until late August. Seeds are dispersed mainly by wind and gravity. The flowers are visited by bumble bees and the plant is subject to insect herbivory. The species is limited to cliff or scarp faces where vegetation is very sparse and interspecific competition is low. In the meadows on Bonaventure Island or along the edges of the tops of escarpments or cliffs, a dense cover of graminoids or low shrubs may limit the species’ expansion.

Population sizes and trends

There are 10 known subpopulations, four of which are historical, but considered extant pending additional search effort. The total known population is 2,742 individuals. However, this is a minimum number, because much of the demographic data are estimates and most sites have only been partially surveyed. The available data do not allow any clear population trends to be determined.

Threats and limiting factors

All potential threats are local in nature. The primary threats are the invasion of the species’ habitat by introduced plants such as Wild Chervil at some of the Bonaventure Island sites, as well as trampling by visitors in places accessible by trail in the Percé area. Although of unknown impact, the expansion of the Northern Gannet breeding colony on this island could also be detrimental to the species. The very small size of most Dense Draba colonies makes them vulnerable to stochastic events such as the collapse of portions of the rock faces where they grow.

Protection, status and ranks

Dense Draba currently has no special status nationally in Canada or internationally. In Québec, it has been designated as threatened since 2010 under the Act Respecting Threatened or Vulnerable Species. It is ranked G1 and N1 (Critically Imperilled) by NatureServe. In Québec, the Centre de données sur le patrimoine naturel du Québec (CDPNQ) ranks it as S1 while it is ranked as SH (possibly extirpated) in Newfoundland. The most significant occurrence is in Île-Bonaventure-et-du-Rocher-Percé Provincial Park and hence on public land. The colonies at L’Anse-Blanchette, Anse-Saint-Georges, and L’Anse-aux-Amérindiens, on the Gaspé Peninsula, are afforded protection from being within Forillon National Park.

Technical summary

Draba pycnosperma
Dense Draba
Drave à graines imbriquées
Range of occurrence in Canada: Québec, Newfoundland and Labrador

Demographic information

Generation time (usually average age of parents in the population; indicate if another method of estimating generation time indicated in the IUCN guidelines (2011) is being used)

Estimated 5-10 years

Is there an [observed, inferred, or projected] continuing decline in number of mature individuals?

No. Suspected decline, based on threats

Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations, whichever is longer up to a maximum of 100 years]

Unknown

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 years, or 3 generations, whichever is longer up to a maximum of 100 years].

Unknown

[Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations, whichever is longer up to a maximum of 100 years].

Suspected decline of <1 – 30 percent over three generations (~ 25 years), based on threat calculator.

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over any period [10 years, or 3 generations, whichever is longer up to a maximum of 100 years], including both the past and the future.

Unknown

Are the causes of the decline a. clearly reversible and b. understood and c. ceased?

a. Unknown

b. Unknown c. Unknown

Are there extreme fluctuations in number of mature individuals?

Unlikely.

Extent and occupancy information

Estimated extent of occurrence (EOO)

67,260 km², including historical sites.

Index of area of occupancy (IAO)

52 km², including historical sites.

Is the population “severely fragmented” i.e., is >50% of its total area of occupancy in habitat patches that are (a) smaller than would be required to support a viable population, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse?

a. No
b. No

Number of “locations”^* (use plausible range to reflect uncertainty if appropriate)

18–23

Is there an [observed, inferred, or projected] decline in extent of occurrence?

No, assuming that all historical sites are extant.

Is there an [observed, inferred, or projected] decline in index of area of occupancy?

No, assuming that all historical sites are extant.

Is there an [observed, inferred, or projected] decline in number of subpopulations?

No, assuming that all historical sites are extant.

Is there an [observed, inferred, or projected] decline in number of “locations”^*?

No.

Is there an [observed, inferred, or projected] decline in [area, extent and/or quality] of habitat?

Yes, observed and inferred decline in quality of habitat.

Are there extreme fluctuations in number of subpopulations?

No

Are there extreme fluctuations in number of “locations”?

No

Are there extreme fluctuations in extent of occurrence?

No

Are there extreme fluctuations in index of area of occupancy?

No

^* See Definitions and Abbreviations on COSEWIC website and IUCN for more information on this term.

Number of mature individuals (in each subpopulation)

Quantitative analysis

Is the probability of extinction in the wild at least [20% within 20 years or 5 generations whichever is longer up to a maximum of 100 years, or 10% within 100 years]? No quantitative analyses have been carried out.

Threats (direct, from highest impact to least, as per IUCN threats calculator)

Was a threats calculator completed for this species? Yes. Assigned Medium-Low threat impact.

Suspected significant threats include:

• Habitat loss and individual mortality due to competition from native and invasive exotic plants (IUCN 7.3 – Medium impact)
• Trampling linked to off-trail visitor traffic (IUCN 6.1 – Low impact)
• Possible loss of habitat and individuals due to the expansion of Northern Gannet breeding colonies (IUCN 8.2 – Unknown impact)
• Destruction of habitat and loss of individuals from rock blasting (IUCN 4.1 – Unknown impact)
• Natural stochastic events of catastrophic magnitude (IUCN 11.1 – Unknown impact)

What additional limiting factors are relevant? Given the small number of occurrences and very limited total population, the establishment of new colonies and the colonization of new microsites with suitable habitat in areas where the species already occurs is problematic. This could be the result of one or more of the following factors: limited annual seed production, low dispersal capacity, inadequate germination rate in natura, and low recruitment rate.

Rescue effect (immigration from outside Canada)

Status of outside population(s) most likely to provide immigrants to Canada

This endemic species is confined to Canada.

Is immigration known or possible?

No.

Would immigrants be adapted to survive in Canada?

Not applicable

Is there sufficient habitat for immigrants in Canada?

Not applicable

Are conditions deteriorating in Canada?⁺

Yes

Are conditions for the source (i.e., outside) population deteriorating?⁺

Not applicable

Is the Canadian population considered to be a sink?⁺

Not applicable

Is rescue from outside populations likely?

No

⁺ See Table 3 (Guidelines for modifying status assessment based on rescue effect)

Data sensitive species

Is this a data sensitive species? No

Status history

COSEWIC Status History: Designated Special Concern in May 2022.

Status and reasons for designation 

Status: Special Concern

Alpha-numeric codes: Not applicable

Reasons for Designation: This small plant occurs on rock outcrops, cliffs, and talus slopes within 2.5 km of the coast along the Gaspé Peninsula and Strait of Belle Isle (Quebec, Newfoundland and Labrador), and is found nowhere else in the world. Fewer than 3000 plants are currently known, occupying a small portion of seemingly abundant suitable habitat. Invasive introduced plant species are degrading the draba’s habitat. As most plant colonies consist of only a few individuals and are associated with steep, dynamic substrates, they may be vulnerable to stochastic events such as rockslides. This species is near to qualifying for Threatened status, and failure to effectively mitigate the threats could result in the species becoming Threatened.

Applicability of criteria

Criterion A (Decline in Total Number of Mature Individuals): Not applicable. Insufficient data to reliably infer, project, or suspect population trends.

Criterion B (Small Distribution Range and Decline or Fluctuation): Not applicable. The IAO of 52 km² meets the threshold for Endangered and there is a continuing decline in habitat quality, but the population occurs in >10 locations, is not severely fragmented, and does not experience extreme fluctuations.

Criterion C (Small and Declining Number of Mature Individuals): Not applicable. Population below threshold for Threatened, but continuing decline is only suspected, extreme fluctuations in number of mature individuals is unknown, and at least one subpopulation has more than 1000 mature individuals and none has more than 95% of mature individuals.

Criterion D (Very Small or Restricted Population): Not applicable. Estimate of > 2,742 mature individuals exceeds thresholds for D1. Although subpopulations vulnerable to stochastic events, impact on population may not result in a rapid and substantial decline.

Criterion E (Quantitative Analysis): Not applicable. Analysis not conducted.

COSEWIC history

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2022)

Wildlife species

A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)

A wildlife species that no longer exists.

Extirpated (XT)

A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A wildlife species facing imminent extirpation or extinction.

Threatened (T)

A wildlife species likely to become endangered if limiting factors are not reversed.

Special concern (SC)
(Note: Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.)

A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at risk (NAR)
(Note: Formerly described as “Not In Any Category”, or “No Designation Required.”)

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data deficient (DD)
(Note: Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” [insufficient scientific information on which to base a designation] prior to 1994. Definition of the [DD] category revised in 2006.)

A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.

^* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
^** Formerly described as “Not In Any Category”, or “No Designation Required.”
^*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006.

The Canadian Wildlife Service, Environment and Climate Change Canada, provides full administrative and financial support to the COSEWIC Secretariat.

Wildlife species description and significance

Name and classification

Scientific name: Draba pycnosperma Fernald and C.H. Knowlt., Rhodora 7: 67. 1905.
Synonyms: Draba canadensis Brunet var. pycnosperma (Fernald and C.H. Knowlt.) O.E. Schulz; D. glabella Pursh var. pycnosperma (Fernald and C.H. Knowlt.) G.A. Mulligan; D. hirta auct. non L. var. pycnosperma (Fernald and C.H. Knowlt.) B. Boivin
English common name: Dense Draba
French common name: Drave à graines imbriquées (Brouillet et al. 2010+)
Family: Brassicaceae (Mustard Family)
Major plant group: Dicotyledons (Magnoliopsida)

Dense Draba was discovered on August 17, 1904 on Cape Blanc in Percé by James Franklin Collins, Merritt Lyndon Fernald, and Arthur Stanley Pease. The following year, Fernald and Knowlton (1905) described it as a distinct species (Figure 1A). Fernald (1934) elaborated on that description and on the geographical distribution of the taxon (Figure 1B). Thereafter, Mulligan (1976) reduced it to a variety of Smooth Draba (Draba glabella), while Al-Shehbaz et al. (2010) reduced it further to a synonym of Smooth Draba, noting however that of all the described segregates of Smooth Draba, this one might warrant taxonomic recognition. Al-Shehbaz and Mulligan (2013) re-evaluated it and re-elevated it to species status while providing an updated morphological description. There is still some debate concerning the validity of this taxon and its taxonomic status, whether it should be recognized as a distinct species or at an infraspecific level under Smooth Draba.

Morphological description

Dense Draba (Figure 2) is a small perennial vascular plant, 5–33 cm tall. This caespitose species arises from a simple or several-branched caudex. The persistent basal rosettes of obovate or oblanceolate leaves are entire or 1–4-dentate. Both leaf surfaces are covered with four-rayed cruciform trichomes, sometimes with spurred rays and thus appearing to have as many as eight branches. The inflorescences are simple or are in branched racemes elongated in fruit. There are one to four pubescent cauline leaves. The 5-40 white flowers (Figure 3A) are borne on divaricate-ascending pedicels, 2–8 mm long. The 3–10 mm long, glabrous or pubescent, inflated and plump fruits (silicles) are oblong to ovoid or ellipsoid (Figure 3B), with a 0.1–0.4-mm-long style. The 1–1.4 x 0.6 mm seeds are overlapping (imbricated) and turned obliquely to the septum (central dividing tissue wall

The most distinctive morphological characteristics of Dense Draba are the inflated silicles, and the obliquely oriented, overlapping seeds (Fernald and Knowlton 1905; Fernald 1934; Al-Shehbaz and Mulligan 2013). This combination of traits is reported to distinguish it from Rock Draba (Draba arabisans) and from the closely related Smooth Draba. Al-Shehbaz and Mulligan (2013) cite several other characters useful in differentiating Dense Draba from Smooth Draba including fewer cauline leaves (1–4 versus 2–17), smaller flowers (sepals 1.5-2 mm versus 2-3.5 mm, petals 2.7-3 mm versus 3.8-4.2 mm), and a leaf indumentum of less-branched trichomes (8-branched versus 7-12 branched).

Population spatial structure and variability

No genetic studies have been conducted on Dense Draba to date. Its genetic links to similar species are unknown, although it is likely most closely related to Smooth Draba, of which it has been reduced to a variety or even a synonym in the past. It often grows in the company of Smooth Draba or Rock Draba, but intergrades have not been reported. In addition, no comparative morphological studies have been conducted on individuals from the species’ various subpopulations around the Gulf of St. Lawrence.

Dense Draba is limited to a few scattered subpopulations immediately bordering the Gulf of St. Lawrence, invariably in exposed, craggy habitats composed of basic rocks. It occupies only a small portion of that habitat, which is fairly abundant in this part of Canada. Despite the presence of usually extensive apparently suitable habitat at a given locality, colonies are most often very small, containing from a few to several dozen widely dispersed individuals. Over 90% of the individuals found to date are in the vicinity of the town of Percé in the Gaspé Peninsula region of Québec.

The subpopulations on the Gaspé Peninsula are separated from the small subpopulation at Blanc Sablon on the Strait of Belle Isle by nearly 600 km. This gap consists mainly of open water, with the only suitable habitat here being on Anticosti Island and in the Mingan region, where the species remains unknown.

Designatable units

No infraspecific entities are recognized for Dense Draba. The Canadian population, which is the only known population worldwide, is limited to several subpopulations along the Gulf of St. Lawrence shoreline. Accordingly, the species is treated as a single designatable unit.

Special significance

Dense Draba is one of a group of Gulf of St. Lawrence “endemic” plants discovered in the early decades of the 20th century by Merritt Lyndon Fernald and associates (e.g., Fernald 1925, 1926, 1933, 1942; Fernald and Weatherby 1931). Members of this group are typically most closely related to, and/or derived from, arctic-alpine species or those with Cordilleran affinities, which persist in this part of Canada as late-glacial relics. These vestiges of an ancient flora have managed to survive in places that the boreal-temperate forest has not been able to colonize since the end of the Wisconsin glaciation and the gradual retreat of the Laurentide Ice Sheet.

From a scientific point of view, the species could serve as a model for studying geographic isolation and morphological and genetic differentiation in relation to speciation.

Distribution

Global and Canadian range

Dense Draba is endemic to Canada, occurring along the shoreline of the Gulf of St. Lawrence in Québec and Newfoundland and Labrador. Its occurrence on the island of Newfoundland is historical, based on collections along the west coast at Doctor Hill (Fernald 1934) in 1925. However, it has not been observed there since, despite search efforts. The population centre within its global range is in the Gaspé Peninsula region of Québec in the vicinity of Percé. This species is also known to occur in three coves on the southern side of Forillon Peninsula, in Forillon National Park, where it was discovered in 1923. In addition, Jacques Rousseau found the species at two sites on the north shore of the Gaspé Peninsula—at Tourelle near Sainte-Anne-des-Monts in 1928 and at Ruisseau du Voile de la Mariée in La Martre in 1934—but it has never been found again at these two sites. Dense Draba was (1999) was discovered at Lourdes-de-Blanc-Sablon, Québec, in the Strait of Belle Isle near the Labrador border in 1999, and a specimen was collected nearby, in Labrador (W of Forteau Point) in 2011.

Dense Draba was also reported from Nova Scotia, in the Lockhart Brook valley on Cape Breton Island (Smith et al., July 9, 1952; ACAD). The specimen was originally identified as Draba clivicola (=D. rupestris). Botanist Alf Erling Porsild then revised it to Dense Draba and Smith subsequently published the record in Rhodora under the latter name (Smith and Erksine 1954). Report writer Benoît Tremblay examined Smith’s herbarium specimen in collaboration with botanists Sean Blaney from the Atlantic Canada Conservation Data Centre and Alain Belliveau from the E.C. Smith Herbarium and revised the identification to Smooth Draba. Consequently, Nova Scotia is removed from Dense Draba’s range.

The Centre de données sur le patrimoine naturel du Québec (CDPNQ) notes 15 occurrences of Dense Draba in Québec which, along with the Newfoundland record, makes for 16 known occurrences globally. Five of these are historical, not having been seen again for at least 40 years. The NatureServe methodology (2020) stipulates that two point locations separated by less than 1 km—or from 1 to 3 km apart, unless there is a gap of unsuitable habitat more than 1 km wide—are considered to form the same element occurrence. In this context, the three occurrences at Forillon National Park could be merged into a single occurrence, as could a number of occurrences in the town of Percé. In the absence of other information, occurrences are considered as subpopulations in this report. Based on this approach and the merging mentioned above, Dense Draba would have 10 distinct subpopulations, four of which are historical (Table 1). Note that historical subpopulations are presumed extant at this time, pending additional search effort.

Total: > 2,742 number of individuals

Extent of occurrence and area of occupancy

The minimum extent of occurrence for Dense Draba is 67,260 km² (Figure 4). However, the vast majority of this area contains unsuitable habitat for the species, primarily open water. The index of area of occupancy (IAO) is made up of 13 cells, each 2 km x 2 km, or a total of 52 km² (9 cells or 36 km² without historical occurrences). The biological area of occupancy was not calculated but represents only a tiny fraction of the IAO.

Search effort

For over a century, considerable effort has been devoted to searching for Dense Draba, both directly and indirectly. The exposed carbonate rock habitats (outcrops, escarpments, sea cliffs, and talus slopes) around the Gulf of St. Lawrence^{Footnote 1}  are well known for their remarkable flora and have been extensively botanized since the early 20^th century. Led by a variety of experienced botanists, these expeditions have produced very few new Dense Draba sites. Dignard (2003) examined over a hundred apparently suitable sites while preparing a provincial report on the species’ status; however, these visits resulted in the addition of only two new occurrences. In the last 20 years, the report writer explored dozens of rocky escarpments, talus slopes, and sea cliffs suitable for the species in the Bic and Rimouski regions, in the Gaspé Peninsula, on Anticosti Island, and on some of the islands in the Mingan region, without discovering a single new site. In addition, Frédéric Coursol spent many days exploring Bonaventure Island in 2002 and again in 2012 (Coursol 2002, 2013). This large island, with roughly 8.5 km of shoreline, is almost completely surrounded by rocky cliffs hospitable to the species, many of which have not been explored or have only been lightly explored to date. Bonaventure Island can therefore be expected to contain more Dense Draba sites and individuals than currently recorded.

Comparable detailed investigations since 1999 in and about the Doctor Hill site in Newfoundland (Hanel pers. comm. 2019) and on the Gaspé Peninsula North Shore (Dignard 2003) have been unsuccessful. Recently, two new sites were discovered: one in Labrador and one in Forillon National Park. It therefore seems prudent to consider the possibility that the species persists at one or more of the historical sites—or at yet undiscovered ones. The rocky escarpments and sea cliffs that make up the species’ preferred habitat are very difficult to access and virtually impossible to explore systematically.

Habitat

Habitat requirements

The Dense Draba population occurs in an area with mean annual temperatures between 0.8˚C and 2.7˚C and total annual precipitation between 1,129 mm and 1,268 mm (inferred from Gérardin and McKenney 2001). It is a rupicolous species, growing exclusively in rocky habitats with non-existent or thin surficial deposits. Although drainage conditions in these habitats range from mesic to xeric, Dense Draba tends to be more xerophytic, most often occupying dry, exposed or partially shaded microsites. It is a calciphile, with all known occurrences having alkaline sedimentary bedrock.

The species has a strong coastal affinity, with most sites located very near the sea, and none further than about 2.5 km inland (historical Newfoundland occurrence).

Dense Draba grows mainly on ledges or benches, in crevices, on rocky escarpments, seaside cliffs, or on large, isolated boulders (Figure 5). It is also sometimes found on talus slopes and on bedrock outcrops in meadows. The species occupies a very narrow strip on the top of the escarpment forming the southern and eastern sides of Mount Sainte-Anne in Percé. This exposed, very windy site has very little vegetation, and is located right next to the cliff edge, just a few metres away from the tall shrub formations or forest growing on the summit. In this marginal habitat, it is often wedged right against the cliff edge by the advancing, dense mats of Creeping Juniper (Juniperus horizontalis). Throughout its range, Dense Draba is patchily and sporadically distributed within its suitable habitat.

Habitat trends

Suitable habitat for Dense Draba is seemingly abundant around the Gulf of St. Lawrence. There are no indications that the area of this habitat has diminished since the discovery of the species over a century ago, or that habitat loss will occur in the foreseeable future. Although the potential habitat is naturally fragmented, the Gulf of St. Lawrence contains long uninterrupted stretches of escarpments composed of basic rocks that could support the species. Throughout its range, however, Dense Draba apparently occupies only a tiny fraction of the locally available suitable habitat. Its rarity may result from intrinsic biological factors such as the number, quality, and viability of seeds produced, their germination rate, seedling survival, dispersal capacity, etc., rather than from lack of habitat.

Some authors have noted a local decline in habitat quality. This is especially the case on Bonaventure Island, where some areas appear to be affected by trampling by visitors, by fluctuations in the area occupied by the Northern Gannet breeding colony, and by the expansion of invasive plant populations (Coursol 2013).

It is difficult to predict how climate change will influence the dynamics of rocky escarpments and how the resulting changes will affect the quality and quantity of Dense Draba habitat. The preferred escarpment habitat is composed of friable sedimentary rocks that are very susceptible to weathering. Weathering in these escarpments is mainly governed by three processes, all of them climatic in nature: frost weathering (freeze-thaw cycles); moisture expansion from liquid precipitation (particularly in these porous rocks); and eolian processes (strength and direction of prevailing winds, squalls, etc.). On sea cliffs, ocean water levels and tidal and wave amplitude also play a role in cliff face weathering. This sun-loving plant requires its habitat to remain open, with relatively sparse vegetation, to avoid undue levels of competition from tall herbaceous or woody vegetation. Should climate change cause decreased precipitation, diminished freeze-thaw cycles, and reduced wind strength and wave action, this could increase cliff and escarpment stability. That in turn could result in the gradual overgrowth of suitable Dense Draba microsites by taller vegetation. Conversely, should climate change contribute to maintaining or amplifying these phenomena, it could help to keep habitats open and create new suitable habitats. What is clear is that the small size of colonies makes them vulnerable to local stochastic phenomena, particularly if the soil seed bank is depleted or non-existent.

Biology

Little is known about the biology of Dense Draba. The following account is based mainly on the report writer’s observations, as well as those of Dignard (2003) and Coursol (2013).

Life cycle and reproduction

Dense Draba is a perennial that survives the winter owing to its caudex, a thickened and lignified portion of the stem at ground level. The caudex lengthens from year to year, and develops branches with time, resulting in a more or less dense carpet of basal rosettes. The species’ longevity is unknown, as is the average age at first flowering although a germination and cultivation experiment (F. Coursol pers. comm. 2019) suggests that age at first flowering is about 5 years (see under next heading). It flowers from the end of May to early July and produces fruits from the second half of June to late August. The raceme and silicles eventually dry up and the valves of the silicles become partially detached, exposing the mature seeds, which are attached to the septum (central dividing tissue wall). Shaking of the stem by repeated gusts of wind releases the seeds, which are dispersed by wind, water, or gravity.

Vegetative reproduction does not occur in the genus Draba. Dense Draba may be able to reproduce sexually through both outbreeding and autogamy. Self-fertilization is known to be very common in the genus, particularly in arctic and alpine species (Mulligan and Findlay 1969; Jordon-Thaden and Koch 2008; Karl and Koch 2013). Dense Draba produces hermaphroditic (perfect) flowers. However, according to Brochmann (1993), autogamous species in this genus are characterized by small, unscented, non-protogynous, and rapidly self-pollinating flowers. Although the flowers of Dense Draba are indeed small and unscented as attributed to self-pollinating taxa, Dignard (2003) reports seeing bumble bees on the flowers, suggesting these insects could be involved in pollination.

Physiology and adaptability

Dense Draba is a calciphile found in a variety of rocky habitats with varying degrees of shade. It seems able to adapt to a fairly wide range of conditions as long as it can access the underlying calcareous rock, the microsite is not too wet, and the vegetation cover is neither too high nor too dense.

Coursol (2013) reports collecting seeds during his inventories on Bonaventure Island in 2012 to determine how easy they are to conserve, and to estimate germination rates. After being collected in July 2012, the seeds were kept at room temperature and then planted in February 2013. Germination was not specifically assessed but was estimated to be near 100%, suggesting limited occurrence in the field is due to other limitations.

The Dense Draba plants cultivated from seed at the Montreal Botanical Garden in 2013 are still alive (Coursol pers. comm. 2019) and produced fruits in 2018.

Dispersal and migration

The seeds of Dense Draba are thin and small and are mainly wind dispersed. They are also dispersed by gravity and likely by water. The widely dispersed subpopulations on the Gaspé Peninsula and the subpopulations 600 km across the Gulf of St. Lawrence in the Strait of Belle Isle area suggest either occasional long-distance dispersal (possibly by birds) or limited persistence within a formerly more continuous range.

The large number of and extent of unoccupied but apparently suitable potential sites around the Gulf of St. Lawrence suggests that dispersal presents a significant constraint on current distribution.

Interspecific interactions

Bumble bees (Bombus spp.) are known to visit the flowers and may be involved in pollination. In addition, an examination of herbarium specimens shows signs of damage to the leaves or fruits from grazing by insects on 91% of specimens (Dignard 2003).

Although interspecific competition is not a constraint in open, rocky habitats, where the vegetation cover is usually very sparse, it does pose a problem in its largest subpopulation in the meadows of Bonaventure Island (Percé area). In this area, the species’ expansion is limited by the areas of dense herbaceous cover, consisting mainly of grasses (Poaceae) and also locally of Wild Chervil (Anthriscus sylvestris), a very aggressive introduced plant (Coursol 2013). Interspecific competition is also observed at the top of rocky escarpments, where the species colonizes the narrow strip of short, sparse vegetation between the cliff edge and nearby tall woody vegetation formations (shrubby and treed areas). Ground-hugging shrubs such as Creeping Juniper often form dense carpets within this strip, limiting colonization opportunities for Dense Draba.

In 2002, Northern Gannet (Morus bassanus) on Bonaventure Island expanded their breeding colony on the eastern side of the island, at the apparent expense of Dense Draba habitat. The situation seemed to have improved in 2012 as the breeding colony had decreased in size in the areas where the main Dense Draba colonies are established (Coursol 2013).

The closely related Smooth Draba and Rock Draba are frequently infected by one or more species of rust, but such infections have never been observed on Dense Draba.

Population sizes and trends

Sampling effort and methods

Sampling activities were not carried out as part of the preparation of this report. The information used to determine the population size comes from:

1. Previous inventories, the most recent being in 2012 (Dignard 2003; Coursol 2013)
2. Occurrence data obtained from the Centre de données sur le patrimoine naturel du Québec (CDPNQ); in many cases, the demographic information provided is the product of estimates rather than precise counts

In the case of the four historical occurrences (one in Newfoundland and three in the Gaspé region), data are only available from herbarium labels, which include no demographic data. In addition, no systematic surveys of any colonies have been conducted to date. There also are no abundance data for any occurrences or subpopulations found before 1999. Accordingly, demographic comparisons over time cannot be made.

In the literature that is available, the inventory methods used by the various authors and the exact area of the habitats searched are not always specified. Consequently, the search effort at the various sites and the proportion of suitable habitat covered at each occupied site cannot be accurately reported or used to establish reliable trends for occurrences that have had repeated visits.

Abundance

A total population of 2,742 individuals has been determined from the most reliable and current information available (Table 1). The proportion of this count made up of mature individuals is not known but it can be assumed that it represents the majority, as detection of seedlings or small immature individuals is likely quite difficult in its habitat, as well as their positive identification to Dense Draba, which frequently grows with other draba species.

This is a minimum number including some estimates, because the potential habitat was not fully searched at all localities. Nevertheless, on the basis of density—which is extremely low in most cases because individuals are found in only a tiny proportion of the potential habitat and considering the unfruitful exploration of scores of suitable habitats by experienced botanists over the last 20 years—it can be reasonably argued that the actual total population is probably not much greater than what is currently known.

It should be noted that the Percé area alone accounts for 91% (2,509) of the total number of individuals enumerated to date. Bonaventure Island, with at least 2,393 individuals in 2012 (87% of the total population), represents the species’ main stronghold.

Fluctuations and trends

Dignard (2003) considers the species to be stable or declining at some sites, primarily in the Percé area. The decline there appears to be due to habitat modifications such as coastal erosion, changes in the physiognomy of the vegetation cover and, on Bonaventure Island, competition from invasive exotic species. No accurate data are available to demonstrate or quantify such a decline. Although the species may be extirpated from certain historical occurrences that have been searched unsuccessfully, the currently available data are insufficient to determine trends in the Dense Draba population.

Rescue effect

Given that Dense Draba is endemic to Canada, there is no possibility of rescue from populations outside the country.

Threats and limiting factors

Threats

Dense Draba is vulnerable to the effects of various threats. These factors are categorized below and in Appendix 1, following the IUCN-CMP (International Union for the Conservation of Nature – Conservation Measures Partnership) unified threats classification system (based on Salafsky et al. 2008). The evaluation assesses impacts for each of 11 main categories of threats and their subcategories, based on the scope (proportion of population exposed to the threat over the next 10-year period), severity (predicted population decline among those exposed to the threat, during the next 10 years or 3 generations, whichever is longer), and timing of each threat. The overall threat impact is calculated by considering the separate impacts of all threat categories and can be adjusted by the species experts participating in the evaluation.

For Dense Draba, the calculated threat impact is Medium; however, the Assigned threat impact, is Medium-Low (see Appendix 1 for details), corresponding to an anticipated decline of between 0.1 and 30% over the next 20-30 years. The actual rate of change is expected to be closer to the low end of this range. Threats are discussed below, in order of decreasing severity of impact.

Dense Draba subpopulations appear to face five main threats:

1. Invasive non-native/alien species/diseases [IUCN 7.3 Other ecosystem modifications]: habitat degradation and competition from invasive exotic. Medium threat impact
2. Recreational activities [IUCN 6.1]: trampling from visitors venturing off marked trails. Low threat impact
3. Problematic native species/diseases [IUCN 8.2]: loss of habitat and individuals linked to the expansion of Northern Gannet breeding colonies. Unknown threat impact
4. Roads and railroads [IUCN 4.1]: destruction of plants and their habitat by blasting from road work. Unknown threat impact
5. Habitat shifting and alteration [IUCN 11.1]: natural stochastic events of a catastrophic magnitude, such as portions of the rock face falling from an escarpment. Unknown threat impact

Each threat only affects certain occurrences, except for natural stochastic events (Habitat shifting and alteration; 11.1), which could impact any colony established on a rocky escarpment or talus slope.

The first three threats listed above primarily or exclusively involve individuals on Bonaventure Island. Coursol (2013) suggests certain colonies could be damaged through trampling by visitors venturing off the trails and approaching the cliff edge. This threat could also affect plants growing near the edge of the escarpment on Mount Saint-Anne (Percé), where there is a hiking trail. Coursol (2002) also cited the expansion of the Northern Gannet breeding colony on the eastern side of Bonaventure Island, where the main Dense Draba colonies occur, as a potential threat. The Bonaventure Island Northern Gannet’s reproductive success seems to undergo significant interannual fluctuations (Gagné 2012; Rail et al. 2013; Shields 2016; Philibert 2017; Fauteux 2018; Bérubé 2019) and impacts on Dense Draba linked to the expansion or reduction of the size of the colony including the spatial extent of the threat are not clear. Lastly, Coursol (2013) reports finding Wild Chervil at roughly 15 of 46 waypoints on Bonaventure Island. This aggressive invasive species, which forms dense monospecific colonies, already represents a threat to Dense Draba at certain sites on the island. Provincial Park employees are trying to prevent the species’ spread, but apparently some colonies are difficult to control or eradicate. Two other introduced invasive plants could eventually threaten certain Dense Draba colonies on Bonaventure Island if their expansion is not curbed: Common Valerian (Valeriana officinalis) and Smooth Bedstraw (Galium mollugo).

Blasting operations on rocky escarpments for road work may have impacted the occurrences in Tourelle and La Martre, or other suitable habitat sites on the rocky cliffs of the north shore of the Gaspé Peninsula between Sainte-Anne-des-Monts and Rivière-Madeleine. There, certain rock faces overlooking the St. Lawrence River have been blasted to provide boulders for riprap along route 132, to protect the road embankment from wave action.

Rock face weathering is a natural process in this habitat. Erosion helps to keep microsites like the escarpment ledges and benches where Dense Draba occurs open by limiting height and density of growth in herbaceous and woody plants. This geomorphological process also helps to create new microsites suitable for the species. However, given the small size of most of the known colonies, a stochastic event of catastrophic magnitude such as the collapse of a portion of a rock face could result in the local extinction of an occurrence. It remains unclear whether climate change will influence rock face erosion dynamics in the future and, if it does, how it may affect Dense Draba or vary among sites.

Limiting factors

The species’ small colony size and affinity for sunny sites are believed to limit its potential colonization and expansion capacities. This is particularly true in the rocky meadows where it grows on Bonaventure Island and on the edges of certain escarpments, where it cannot compete with the graminoids or low or creeping shrubs that form a dense cover. However, the main factors responsible for the species’ extreme rarity and small total population are not clear. As explained earlier, these factors are probably biological in nature and linked to the quality and quantity of seeds produced annually, low dispersion capacity as well as germination and recruitment rates, which are all likely low in the natural environment.

Because all the potential threats to the species are local in extent and would occur independently at a given site, almost every habitat where the plant is found in a given place could be considered to represent a location—for example, an escarpment, talus slope, isolated boulder. or coastal meadow that contains one or more closely spaced colonies. Therefore, Dense Draba has 23 locations, 18 if historical locations are excluded, with Bonaventure Island itself containing nine locations.

Protection, status and ranks

Legal protection and status

Dense Draba has no legal global or national protective status. In Québec, it has been designated Threatened since 2010 under the Act Respecting Threatened or Vulnerable Species(R.S.Q., chapter E-12.01). According to Section 16 of the Act, no person may have any specimen of a threatened or vulnerable plant species or any of its parts, including its progeny, in their possession outside its natural environment, or harvest, exploit, mutilate, destroy, acquire, transfer, offer to transfer or genetically manipulate it.

Non-legal status and ranks

Dense Draba is ranked Critically Imperilled (G1 and N1) both globally and in Canada (NatureServe 2019), Critically Imperilled (S1) in Québec (Tardif et al. 2016) and Possibly Extirpated (SH) in Newfoundland (NatureServe 2019). It has not been assessed yet by the International Union for Conservation of Nature (IUCN).

Habitat protection and ownership

The most significant subpopulation of the species, on Bonaventure Island, is within Île-Bonaventure-et-du-Rocher-Percé Provincial Park. The sea cliffs subpopulation at L’Anse-Blanchette, Anse-Saint-Georges, and L’Anse-aux-Amérindiens is in Forillon National Park. All the sites in the vicinity of Percé are within the Percé UNESCO Global Geopark (Géoparc mondial UNESCO de Percé 2019); however, these geoparks do not convey any legal-based protection. The individuals on Mount Saint-Anne, on Cape Blanc and in the Birmingham Brook area in Percé are on private land. The ownership of the land containing other recent or historical occurrences of the species in Québec is unknown. The historical site in Newfoundland is on provincial Crown land proposed for protection as an Ecological Reserve under the Protected Areas Plan for the Island of Newfoundland (Wilderness and Ecological Reserves Advisory Council 2020).

Acknowledgements and authorities contacted

The report writer would like to express his gratitude to the following individuals who provided information and comments on the Dense Draba:

Adam Durocher, Data Manager, Atlantic Canada Conservation Data Centre

Claudia Hanel, Ecosystem Management Ecologist, Botanist; Wildlife Division, Department of Fisheries and Land Resources, Government of Newfoundland and Labrador

Frédéric Coursol, Assistant Botanist, Montreal Botanical Garden

Sean Blaney, Executive Director and Senior Scientist, Atlantic Canada Conservation Data Centre

The report writer also warmly thanks Jacques Labrecque and Vincent Piché from CDPNQ. Huge thanks also go to Frédéric Coursol for authorizing the reproduction of his photographs of Dense Draba and its habitat, as well as to Melanie Schori, Editor-in-Chief of the journal Rhodora, for permission to reproduce the illustrations from two articles by M.L. Fernald. The writer also extends his heartfelt thanks to Alain Belliveau, Botanist and Collections Manager of the E.C. Smith Herbarium at Acadia University, who kindly provided numerous morphological comments on a herbarium specimen of Draba glabella from Cape Breton, previously identified as D. pycnosperma. Lastly, he would also like to thank the members of COSEWIC’s Vascular Plants Specialist Subcommittee, particularly Del Meidinger.

Information sources

Al-Shehbaz, I., M.D. Windham, and R. Elven. 2010. Draba Linnaeus. Pp. 269–347 in Flora of North America Editorial Committee, eds. Vol. 7: Magnoliophyta: Salicaceae to Brassicaceae. Oxford University Press, New York.

Al-Shehbaz, I., and G.A. Mulligan. 2013. New or noteworthy species of Draba (Brassicaceae) from Canada and Alaska. Harvard Papers in Botany 18:101-124.

Bérubé, J. 2019. Année difficile pour le fou de Bassan de l'île Bonaventure. Radio Canada broadcast on September 6, 2019. Website: [accessed October 2019].

Brochmann, C. 1993. Reproductive strategies of diploid and polyploid populations of Arctic Draba (Brassicaceae). Plant Systematics and Evolution 185:55-83.

Brouillet, L., F. Coursol, S.J. Meades, M. Favreau, M. Anions, P. Bélisle, and P. Desmet. 2010+. Draba pycnosperma Fernald and Al-Shehbaz in VASCAN, Canadian vascular plant database. Website: [accessed October 2019].

Coursol, F. 2002. Inventaire des plantes menacées ou vulnérable ou susceptible d’être ainsi désignées au Parc national de l’Île-Bonaventure-et-du-Rocher-Percé. Gouvernement du Québec, Société de la faune et des parcs du Québec, Direction de l’expertise professionnelle et technique, Québec. 16 p.

Coursol, F. 2013. Inventaire des plantes menacées ou vulnérable ou susceptible d’être ainsi désignées au Parc national de l’Île-Bonaventure-et-du-Rocher-Percé. Gouvernement du Québec, Société des établissements de plein air du Québec, Québec. 33 p.

Coursol, F., pers. comm. 2019. Email to B. Tremblay. November 2019. Assistant Botanist, Montreal Botanical Garden, Montreal, Quebec.

Dignard, N. 2003. La situation de la drave à graines imbriquées (Draba pycnosperma) Fernald and C.H. Knowlton) au Québec. Herbier du Québec, Direction de la recherche forestière, ministère des Ressources naturelles, unpublished report prepared for the Centre de données sur le patrimoine naturel du Québec, ministère de l’Environnement. 19 p.

Fauteux, H. 2018. La population de Fous de Bassan prend progressivement du mieux. Radio CFIM broadcast on October 22, 2018.

Fernald, M.L. 1925. Persistence of plants in unglaciated areas of boreal America. Memoirs of the American Academy of Arts and Sciences 15:237-342.

Fernald, M.L. 1926. Two summers botanizing in Newfoundland (continued). Rhodora 28:115-129.

Fernald, M. L., 1933. Recent discoveries in the Newfoundland flora. Rhodora 35:1-16, 80-107, 298-315.

Fernald, M.L. 1934. Draba in Temperate Northeastern America (continued). Rhodora 36:314-372.

Fernald, M. L. 1942. Incidents of field-work with J. Franklin Collins. Rhodora 44:98-147.

Fernald, M.L., and C.H. Knowlton. 1905. Draba incana and its allies in North-Eastern America. Rhodora 7(76):61-67.

Fernald, M.L., and C.A. Weatherby. 1931. Some new plants from the Gaspé Peninsula. Rhodora 33:231-240.

Gagné, G. 2012. Île Bonaventure: la colonie de fous de Bassan en déclin. Article published in Le Soleil, September 14, 2012.

Gerardin, V., and D. McKenney. 2001. Une classification climatique du Québec à partir de modèles de distribution spatiale de données climatiques mensuelles: vers une définition des bioclimats du Québec. Ministère de l’Environnement du Québec, Direction du patrimoine écologique et du développement durable, Québec. 40 p.

Hanel, C., pers. comm. 2019. Email to B. Tremblay. December 2019. Ecosystem Management Ecologist, Botanist, Wildlife Division, Department of Fisheries and Land Resources, Government of Newfoundland and Labrador.

Jordon-Thaden, I., and M.A. Koch. 2008. Diversity patterns in the genus Draba: a first global perspective. Plant Ecology and Diversity 1:255-263.

Karl, R., and M.A. Koch. 2013. A world-wide perspective on crucifer speciation and evolution: phylogenetics, biogeography and trait evolution in tribe Arabideae. Annals of Botany 112:983-1001.

Mulligan, G.A. 1976. The genus Draba in Canada and Alaska: key and summary. Canadian Journal of Botany 54:1386–1393.

Mulligan, G.A., and J.N. Findlay. 1969. Sexual reproduction and agamospermy in the genus Draba. Canadian Journal of Botany 48:269-270.

NatureServe. 2019. NatureServe Explorer, an online encyclopedia of life: Draba pycnosperma – Fern. & Knowlt. [accessed November 2019].

NatureServe. 2020. Website: Habitat-based Plant Element Occurrence Delimitation Guidance [PDF] [accessed December 2020].

Percé UNESCO Global Geopark. 2019. Géoparc Mondial UNESCO de Percé. Website: [accessed November 2019].

Philibert, G. 2017. La population de fous de Bassan se stabilise sur l’île Bonaventure. Radio Gaspésie broadcast on May 19, 2017.

Rail, J.-F., L. Champoux, R.A. Lavoie, and G. Chapdelaine. 2013. Monitoring of the population and contamination of the Northern Gannet in Quebec, 1966-2009. Technical Report Series No. 528. Canadian Wildlife Service, Quebec Region, Environment Canada, Quebec. ix + 75 pages + appendices.

Salafsky, N., D. Salzer, A.J. Stattersfield, C. Hilton‐Taylor, R. Neugarten, S.H. Butchart, B. Collen, N. Cox, L.L. Master, S. O'Connor, and D. Wilkie. 2008. A standard lexicon for biodiversity conservation: unified classifications of threats and actions. Conservation Biology 22:897-911.

Shields, A. 2016. Fous de Bassan de l’île Bonaventure: une colonie fragilisée. Article published in Le Devoir, August 27, 2016.

Smith, E.C., and D.S. Erksine. 1954. Contributions to the flora of Nova Scotia IV. Rhodora 56:242-252.

Tardif, B., B. Tremblay, G. Jolicoeur, and J. Labrecque. 2016. Les plantes vasculaires en situation précaire au Québec. Centre de données sur le patrimoine naturel du Québec (CDPNQ). Gouvernement du Québec, ministère du Développement durable, de l’Environnement et de la Lutte contre les changements climatiques (MDDELCC), Direction de l’expertise en biodiversité, Québec. 420 p.

Wilderness and Ecological Reserves Advisory Council. 2020. A Home for Nature: Protected Areas Plan for the Island of Newfoundland [PDF].

Biographical summary of report writer

Benoît Tremblay has a B.Sc. in biology with specialization in ecology from the Université du Québec à Rimouski (UQAR) and a Master’s in arctic plant ecology from the Université du Québec à Trois-Rivières (UQTR). He has been working as a botanist for more than 20 years, both as an independent consultant and as an employee of academic institutions and the Government of Quebec. An expert in arctic environments, he has conducted a large number of plant and phytosociology surveys since 2003 and has written several works on the flora, vegetation and ecosystems of Nunavik. During his many years of field experience, he has developed in-depth knowledge of Quebec’s flora and ecosystems, particularly those of High-Boreal and Arctic regions and of the Gulf of St. Lawrence. He is a member of the advisory committee on threatened and vulnerable flora of Quebec. Since 2017, he has been project manager, conservation of threatened and vulnerable flora with the Quebec Department of Environment and the Fight Against Climate Change.

Collections examined

E.C. Smith Herbarium, Acadia University (ACAD) Smith et al. 6376, July 9, 1952 (Nova Scotia, Lockhart Brook), revised to Draba glabella Pursh

Benoît Tremblay’s personal herbarium Tremblay s.n., June 19, 2002 (Quebec, town of Percé, Mount Sainte-Anne) Tremblay s.n., June 19, 2002 (Quebec, town of Percé, Logan Rock)

Appendix 1. threat assessment for Dense Draba

Threats assessment worksheet

Species or ecosystem scientific name:

Draba pycnosperma

Element ID:

Element_global.2.141969

Elcode:

PDBRA113D0

Date:

2020-11-03

Assessor(s):

Del Meidinger (moderator, SSC Co-Chair), Benoît Tremblay (report writer), Danna Leaman (VP SSC), Stephanie Pellerin (VP SSC), Jacques Labrecque (QC), Jana Vamosi (SSC Co-Chair), David Mazerolle (VP SSC), Dan Brunton (VP SSC), Paul Knaga (CWS), Jessica Humber (NL), Angèle Cyr (Secretariat), Bruce Bennett (VP SSC) Fred Coursol, Antoine Plouffe-Leboeuf (Parks Canada)

References:

Coursol (2002, 2013)

Assigned overall threat impact:

CD = Medium - Low

Impact adjustment reasons:

Habitat alteration by invasive species is the main threat and although the impact may be Medium, as calculated, due to the difficulty of managing the invasives in the Draba habitat, it could also be in the Low impact range due to uncertainty in expansion of the invasive species. As such, the impact was assigned Medium-Low.

Overall threat comments:

Generation time of 5-10 yrs; for purposes of threats assessment, three generation time frame about 25 (20-30) yrs. Most of population on Bonaventure Island

Classification of Threats adopted from IUCN-CMP, Salafsky et al. (2008).