Forked Bluecurls (Trichostema dichotomum): COSEWIC assessment and status report 2023

Official title: COSEWIC assessment and status report on the Forked Bluecurls (Trichostema dichotomum) in Canada

Threatened

2023

COSEWIC assessment summary

Assessment summary – December 2023

Common name

Forked Bluecurls

Scientific name

Trichostema dichotomum

Status

Threatened

Reason for designation

In Canada, this annual mint grows on open dry sand deposits and acidic rocky barrens at only a few sites in southern Ontario, Quebec, and Nova Scotia. Over the past 10 years, the Canadian population declined by at least 50%, to 3200-3700 mature individuals. Although factors causing declines are not fully understood, most current threats relate to human activities that disrupt natural ecological processes, such as fire suppression and competition from native and invasive species in habitats affected by human development.

Occurrence

Nova Scotia, Ontario, Quebec

Status history

Designated Threatened in December 2023.

COSEWIC executive summary

Forked Bluecurls

Trichostema dichotomum

Wildlife species description and significance

Forked Bluecurls is a small annual flowering plant in the Mint family. The common name of this species refers to the arching stamens of the delicate blue flowers.

This species occurs only in sparsely vegetated open areas on acidic, dry to mesic, sandy or gravelly mineral soils, in habitats that are important to several other species that are considered rare or at risk in Canada. The Canadian population is at the northern edge of its global range.

Aboriginal (Indigenous) Knowledge

All species are significant and are interconnected and interrelated. There is no species-specific ATK in the report.

Distribution

Forked Bluecurls is found across eastern North America, from Texas, Florida and the Bahamas, north to Ontario, Quebec and Nova Scotia, in southeastern Canada. Less than 1% of the global range and global population of this species occurs in Canada.

Habitat

Across its range, Forked Bluecurls is found in a variety of natural habitats, including barrens, rock outcrops, prairies and open woods. It also occurs in open habitats associated with human disturbance such as sandy fields and roadsides. In its core range in the southeastern United States, this species tends to be a generalist and can tolerate a wide range of soil moisture and pH conditions, but prefers full to partial sun. In the northern part of its range, including the Canadian portion, its habitat requirements are more restrictive, and Forked Bluecurls is typically found only on acidic, dry to mesic, sandy or gravelly mineral soils in sparsely vegetated open areas. There are regional differences in the habitat across the Canadian population.

Biology

Forked Bluecurls completes its life cycle in a single growing season. In Canada, flowering begins in late July, peaks in mid-August and tapers off by early September. The number of flowers per plant varies with plant size, ranging from fewer than 10 to more than 250. In ideal circumstances, it can produce large numbers of seeds. If conditions are suitable, most seeds germinate the following year, but some seeds can persist in a seed bank for future years. As with other annual plant species, seed banking is critical in years with poor survival, flowering or seed set. Seed longevity is uncertain. The fruits do not have any specialized dispersal mechanisms, and long-distance dispersal is considered rare.

Forked Bluecurls requires loose, exposed mineral soils and high light levels to germinate and thrive. It is not able to compete with dense ground cover or shade-casting vegetation. In Canada, it is likely limited by climatic conditions. This species is drought and fire tolerant. Natural or anthropogenic disturbances that expose mineral soils, reduce ground cover and maintain an open canopy can be beneficial for this species, provided that disturbance is not so great that it results in the complete loss of the seed bank or in excessive plant mortality.

Population sizes and trends

The current population of Forked Bluecurls in Canada is estimated to be in the range of 3,200 to 3,700 mature individuals. This is a minimum estimate, as it is based on late summer or early fall counts (or visual estimates) of individual plants at known sites in recent years by various observers. These known sites are thought to represent most of the population, although a few additional subpopulations or sites may exist.

Overall, the Canadian population of Forked Bluecurls appears to have declined by more than 50% over the past 10 years as a result of the large declines observed at four of the nine subpopulations. Longer term trend information is not available.

Threats

The main threat to Forked Bluecurls in Canada is the general disruption of ecological processes at many sites in Ontario and Quebec. In the absence of natural or human disturbances, the growth of native and non-native plant species can rapidly cause the habitat to become unsuitable for this species. The overall threat impact for Forked Bluecurls is considered to be Medium to Low.

Protection, status, and recovery activities

Forked Bluecurls currently has no federal or provincial legal protection or status in Canada. Globally, this species is considered Secure (G5). In Canada, Forked Bluecurls is ranked Critically Imperiled to Imperiled (N1N2), and Critically Imperiled (S1) in the three provinces where it is present (Ontario, Quebec and Nova Scotia). About half of the current population occurs on protected lands, including a provincial conservation reserve in Ontario, a voluntary protected area in Quebec, and a provincial wilderness area in Nova Scotia.

Technical summary

Trichostema dichotomum

Forked Bluecurls

Trichostème fourchu

Range of occurrence in Canada: Nova Scotia, Ontario, Quebec

Demographic information:

Generation time (usually average age of parents in the population)

Approximately 3 years

Based on a one-year life cycle and most seeds germinating in the first two years

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

Observed

Overall reduction of at least 60%, driven largely by marked population declines in four of the nine known subpopulations in the past ten years

[Observed, estimated, or projected] percent of continuing decline in total number of mature individuals within 3 years [or 1 generation; whichever is longer up to a maximum of 100 years]

Unknown

Unknown

Observed, estimated, or projected] 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

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]

Estimated overall reduction in known subpopulations of more than 50% over the last 10 years

Available information limited, but inferred > 50% overall reduction over 10 years, due to observed large decline in abundance in four subpopulations with comparable repeated surveys (SP#6, #7, #9 and #10). Limited incidental data on three other subpopulations suggest possible small increase at SP#3, and no apparent change at SP#4 and #5. No recent data for SP#8. No past data for SP#11.

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

Unknown

Unknown

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

Unknown

Declines have been observed in the past, and it is unknown whether the declines will continue.

Are the causes of the decline clearly reversible?

Unknown

Uncertain as related to land use activities on private land

Are the causes of the decline clearly understood?

No

Some declines presumably due to changes to disturbance regime and related habitat succession, but cause of decline at one site (7A) is unknown

Are the causes of the decline clearly ceased?

No

Habitat succession is ongoing at some sites.

Are there extreme fluctuations in number of mature individuals

No

Annual variability, but persistent seed bank

Extent and occupancy information:

Estimated extent of occurrence (EOO)

103,766 km²

Calculated based on minimum convex polygon around extant occurrences between 2003 and 2022

Index of area of occupancy (IAO), reported as 2x2 km grid value

52 km²

All extant subpopulations between 2003 and 2022

Is the population “severely fragmented”, that is, is >50% of individuals or >50% of the total area “occupied” (as a proxy for number of individuals) in habitat patches that are both (a) smaller than required to support a viable subpopulation, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse?

1. No
2. No

There is a minimum viable subpopulation, and expected dispersal distances are unknown, but the species can persist in small, scattered habitat patches.

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

At least 13

Locations are defined based on land ownership, as effects of threats are expected to differ at each location based on land management practices.

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

No

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

Possibly

Saint-Chrysostome is historical and may be extirpated in the next 10 years.

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

Possibly

Saint-Chrysostome is historical and may be extirpated in the next 10 years.

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

Possibly

Saint-Chrysostome is historical and may be extirpated in the next 10 years.

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

Unknown

A past decline in habitat contributed to the population decline. No net decline is expected as future habitat trends on private sites mostly unknown and beneficial management ongoing or anticipated at some sites (3A, 3B, 3C, 7A).

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

Number of mature individuals (by subpopulation):

Quantitative analysis:

Is the probability of extinction in the wild at least 20% within 20 years [or 5 generations], or 10% within 100 years]

Unknown

Analysis not conducted

Threats:

Was a threats calculator completed for this species?

Yes, in January 2023 (see Appendix 2)

Overall assigned threat impact: Medium - Low

Key threats were identified as:

1. Natural System Modification (IUCN 7) – Medium - Low
2. Agricultural and Aquaculture (IUCN 2) – Unknown

What limiting factors are relevant?

• It requires loose, exposed, dry soils and high light levels to germinate and thrive
• It is not able to compete with dense ground cover or under shade-casting vegetation.
• It is likely limited by climatic conditions in the northern part of its range.

Rescue effect (from outside Canada):

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

Stable

Secure (S5) in New York and Imperiled (S2) in Michigan. Status not assessed but likely Apparently Secure (S4) in Ohio, Vermont, New Hampshire and Maine.

Is immigration known or possible?

Unknown

Unknown, but considered unlikely

Would immigrants be adapted to survive in Canada?

Yes

Environmental conditions in Canadian range are similar to those in northern part of U.S. range.

Is there sufficient habitat for immigrants in Canada?

Yes

Potentially suitable habitat is present locally in the Canadian range.

Are conditions deteriorating in Canada?

Unknown

Habitats likely to improve at some sites with active management, but future habitat trends at other sites on private land are mostly unknown.

Are conditions for the source (that is, outside) population deteriorating?

No

Potential source population in northern U.S. generally considered stable, except for ongoing habitat loss in Ohio and Michigan where the species is Threatened

Is the Canadian population considered to be a sink?

No

Species has persisted at one site for 50+ years and no evidence of immigration.

Is rescue from outside Canada likely, such that it could lead to a change in status?

No

Human-assisted introduction events will likely occur occasionally in southern Ontario and southern Quebec, but rescue is not considered a major factor mitigating conservation concern for the native Canadian population.

Wildlife species with sensitive occurrence data (general caution for consideration):

Could release of certain occurrence data result in increased harm to the Wildlife Species or its habitat?

No

Availability of occurrence data is unlikely to result in trampling by observers or intentional habitat destruction.

Status history:

COSEWIC:

Designated Threatened in December 2023.

Status and reasons for designation:

Status

Threatened

Alpha-numeric codes

Met criteria for Endangered, A2ace, but designated Threatened, A2ace, because the wildlife species is not at imminent risk of extirpation.

Reason for change in status

Not applicable.

Reasons for designation

In Canada, this annual mint grows on open dry sand deposits and acidic rocky barrens at only a few sites in southern Ontario, Quebec, and Nova Scotia. Over the past 10 years, the Canadian population declined by at least 50%, to 3200-3700 mature individuals. Although factors causing declines are not fully understood, most current threats relate to human activities that disrupt natural ecological processes, such as fire suppression and competition from native and invasive species in habitats affected by human development.

Applicability of criteria:

A: Decline in total number of mature individuals:

Meets Endangered, A2ace.

There is an observed decline of greater than 50% in the number of mature individuals over the past ten years, based on direct observation, decline in the quality of habitat, and competition from native and introduced taxa.

B: Small range and decline or fluctuation

Not applicable.

IAO of 52 km² is below the threshold for Endangered, but the population is not severely fragmented, occurs at > 10 locations, and does not experience extreme fluctuations.

C: Small and declining number of mature individuals

Not applicable.

May meet Threatened, C1. The number of mature individuals (3,200 to 3,700) is below the threshold for Threatened, and there is a decline of more than 10% over 10 years/3 generations. However, there are no data to estimate a continuing decline in the future. There are no extreme fluctuations in the number of mature individuals, and at least one subpopulation has more than 1,000 mature individuals, although no subpopulation contains more than 95% of mature individuals.

D: Very small or restricted population

Not applicable.

Estimate of 3,200 to 3,700 mature individuals exceeds thresholds for D1. Threatened D2 not applicable. IAO and number of locations exceed thresholds, and population is not vulnerable to rapid and substantial decline.

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 (2019)

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.

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

Current classification:

Major plant group: Angiosperm (eudicot flowering plant)

Order: Lamiales

Family: Lamiaceae (Mint Family)

Genus: Trichostema

Species: Trichostema dichotomum

Common names: (National General Status Working Group 2022)

English: Forked Bluecurls

French: Trichostème fourchu

Synonyms and notes:

Of the sixteen accepted species in the North American genus Trichostema, three occur in Canada. Fluxweed (T. brachiatum) occurs locally in southern Ontario and southern Quebec, typically in alvar habitats. Oblong Bluecurls (T. oblongum) is a western species that occurs very locally in southern British Columbia. No synonyms or infraspecific taxa are recognized (ITIS 2022; NatureServe 2022).

Description of wildlife species

Forked Bluecurls is a small, erect, aromatic annual plant arising from a taproot. In Canada, mature individuals range in height from 3 cm to 50 cm. Small individuals are single stemmed but larger individuals are typically multi-branched (cover photo). The stems are square sided with a glandular pubescence. The leaves are opposite, entire, and oblong to lanceolate.

Numerous small delicate flowers, 4 to 6 mm long, form on stems arising from the leaf axils. The asymmetric blue-purple flowers are distinctive. The centre of the lower lip is light-coloured with dark purple spotting. Four elongate forked stamens form a curving arch extending over the flower. The common name of this species refers to this feature.

The fruits consist of up to four partially fused nutlets, each 1 to 2 mm across and containing a single seed, that are produced in a distinctive asymmetric cup-like structure formed by the rotated flower calyx (Figure 1).

Fluxweed has a similar appearance, but its five-lobed flowers are much more symmetric. Several other species in the Mint (Lamiaceae) and Figwort (Scrophulariaceae) families are structurally similar, but are readily distinguished when flowering or fruiting.

Figure 1. Forked Bluecurls plant with flower buds at ends of stem, flower with exerted stamens, and developing fruits (nutlets) in the cup-like structure formed by the calyxes. Photo by A. Heagy, 15 August 2022, Turkey Point (SP#3), Ontario. Used with permission.

Designatable units

The Forked Bluecurls population is considered a single designatable unit (DU). Although the subpopulation in Nova Scotia is separated from the nearest occurrence in the United States by a major water barrier of more than 250 km (Figures 2, 3), and is in a different ecological area and occupies a different habitat type than the Ontario and Quebec subpopulations, the evolution of significant adaptations is not expected since the species occurs in similar habitat and climatic conditions across the northern part of its range in eastern North America (Figure 2). Outside of Florida and the southernmost Atlantic coastal plain, this species appears to be morphologically homogeneous (McClelland pers. comm. 2022). The genetic structure across the northern range of this species has not been investigated.

Figure 2. Global distribution of Forked Bluecurls. The dark green indicates jurisdictions where the species is present and native. Occupied counties within jurisdictions where the species is rare (yellow) or not rare (light green) are indicated. Counties in Canada where the species is considered extirpated (orange) or adventive (pink) are also indicated. Modification of map generated from Kartesz, J.T. 2015. Floristic Synthesis of North America, Version 1.0. Biota of North America Program (BONAP) (in press). Used with permission.

Special significance

Forked Bluecurls subpopulations in Canada are on the northern periphery of their global range. Populations at the edge of a species’ range may be important for the future adaptive potential of the species (Lesica and Allendorf 1995).

Aboriginal (Indigenous) knowledge

Aboriginal Traditional Knowledge (ATK) is relationship-based. It involves information on ecological relationships between humans and their environment, including characteristics of species, habitats and locations. Laws and protocols for human relationships with the environment are passed on through teachings and stories, and Indigenous languages, and can be based on long-term observations. Place names provide information about harvesting areas, ecological processes, spiritual significance or the products of harvest. ATK can identify life history characteristics of a species or distinct differences between similar species.

Cultural significance to indigenous peoples

There is no species-specific ATK in the report. However, Forked Bluecurls is important to Indigenous Peoples who recognize the interrelationships of all species within the ecosystem.

Distribution

Global range

Forked Bluecurls occurs across eastern North America, from Texas, Florida and the Bahamas north to southeastern Canada (Figure 2). This species is common in the southeastern United States and much of the northeastern United States, but is rare in several jurisdictions on the northern periphery of its range, including the states of Indiana and Michigan and the provinces of Nova Scotia, Ontario and Quebec (Kartesz 2015; NatureServe 2022).

Canadian range

Less than 1% of the global range and population of Forked Bluecurls occurs in Canada. The Canadian population consists of eleven presumed native subpopulations located in southwestern Ontario, southwestern Quebec and southern Nova Scotia (Figure 3, Table 1, Appendix 1).

This species has long been reported as part of the flora of eastern Canada (for example, Drummond 1868), but most subpopulations have been found relatively recently (Table 1). The bases of the earliest reports are unknown, as the oldest known specimens from Canada were collected from Île à Paquette near La Prairie, Quebec (SP#1) in July 1920 (MT49705, MT49706) and from Missisquoi Bay near the mouth of Rivière-aux-Brochets, Quebec (SP#2) in August 1952 (MT49704). It has been suggested that the specimens collected in 1920 might have actually come from Maine and were incorrectly labeled (see Montgomery and Morton 1973; Morton 1987), but this record is now accepted as an element occurrence by the Quebec conservation data centre, Centre de données sur le patrimoine naturel du Québec (CDPNQ) (2022). There are no additional records for the La Prairie and Baie Missisquoi subpopulations (SP#1 and #2), both of which are considered extirpated (Morton 1987; CDPNQ 2022). Forked Bluecurls was considered adventive^{Footnote 1} in Quebec (Marie-Victorin et al. 1995) prior to the discovery of several presumed native occurrences (SP#6, #7, #8, #9 and #10) in southwestern Quebec between 2011 and 2013 (Sabourin and Bélair 2014). The first record of the species in Ontario is a presumed native occurrence discovered in 1971 near Turkey Point, Ontario (SP#3) (Montgomery and Morton 1973; Oldham and Brinker 2009; Figure 4). Additional sites have been found in the Turkey Point subpopulation, and the two other Ontario subpopulations (SP#4, #11) are about 5 km away (Map 2, Table 1, Appendix 1). The only occurrence in Atlantic Canada is a small subpopulation (SP#5) found in 2011 at a natural site near Shingle Lake in southern Nova Scotia (Figure 5).

A subpopulation found in 1990 at an abandoned railway yard near St. Thomas, Ontario (SP-X) is presumed to have been introduced from seed from the United States population via train traffic, since it occurred only in highly disturbed ground (railway ballast) with non-native associates, no potential natural habitat exists in the vicinity, and it is 50 km west of the nearest native subpopulation in Canada (Oldham and Brinker 2009; Oldham 2018). The occurrence was only seen once and was not believed to have become established. This adventive subpopulation is not considered part of the Canadian population or range (Figure 3). A specimen from Pointe-des-Cascades, Quebec, reported as Forked Bluecurls in an online biodiversity database (GBIF 2022) has been identified as Fluxweed (Labrecque pers. comm. 2022).

Figure 3. Canadian subpopulations of Forked Bluecurls (map courtesy of A. Filion, COSEWIC Secretariat).

Figure 4. Forked Bluecurls (yellow flags) growing along the margins of an unauthorized off-road vehicle trail along a powerline right-of-way through a pine plantation. Photo by A. Heagy, 15 August 2022, Turkey Point (SP#3), Ontario. Used with permission.

Figure 5. Forked Bluecurls habitat, Shingle Lake rock barren (SP#5), Nova Scotia. Photo by S. Blaney. Used with permission.

Extensive general botanical effort has been expended within the potential range and habitat of Forked Bluecurls in Canada. Recent targeted fieldwork for this species has focused on the immediate vicinity of the known extant sites (see Population Size and Trends). The species is readily identifiable, although relatively inconspicuous outside of the flowering and fruiting period in late summer. Detectability is also high during this period, as it typically occurs in sparsely vegetated openings. The small number of localized subpopulations reported historically or recently indicates that this species is rare and is evidently absent from most potential habitat. A few additional localized sites in the vicinity of the known subpopulations are expected, particularly on private land holdings in southwestern Ontario and southwestern Quebec or in other remote rock barren openings in southern Nova Scotia. The species could also potentially occur locally in southeastern Ontario or southern New Brunswick in proximity to subpopulations in the United States (see Figures 2 and 3, and Rescue effect).

The subpopulations in Ontario and Quebec occur within the Great Lakes Plain Ecological Area (COSEWIC 2020). The Nova Scotia subpopulation is in the Atlantic Ecological Area (COSEWIC 2020).

Population structure

In this report, a site refers to a private land parcel or public land management unit with one or more patches of Forked Bluecurls; a subpopulation refers to one or more sites separated by a maximum of 1 km (unless linked by a waterway or other special cases as defined by NatureServe); the population refers to all subpopulations in Canada. This definition of subpopulation is consistent with the COSEWIC definition, as gene flow through insect-vectored pollen transfer between patches separated by more than 1 km is unlikely. The term subpopulation is consistent and used interchangeably with the NatureServe term “element occurrence” (EO) (NatureServe 2020, 2022) as used by regional conservation data centres for this species in Canada. The use of a 1-km separation appears warranted as the distribution of suitable habitat is patchy rather than continuous, and natural disturbance regimes affecting landscape-scale habitat dynamics have either been permanently interrupted (Ontario and Quebec subpopulations) or occur over longer than a 25-year cycle (Nova Scotia subpopulation).

The spatial distribution of Forked Bluecurls in Canada, and across the northern part of its global range in general, is discontinuous (Figures 2 and 3). The cluster of subpopulations in Ontario is some 500 km southwest of the cluster of subpopulations in Quebec, and about 100 km north (across Lake Erie) of the closest sites in the United States. The Quebec subpopulations are within 50 km of sites in the United States. The Nova Scotia subpopulation is more than 600 km east of the Quebec subpopulations and 250 km east (across the Bay of Fundy) of the closest sites in the United States.

No genetic structure in the population is known (see Designatable units).

Extent of occurrence and area of occupancy

Sites and subpopulations are classified as extant or extirpated according to the NatureServe terminology as used by the Canadian conservation data centres (Ontario Natural Heritage Information Centre [ONHIC], CDPNQ, and Atlantic Canada Conservation Data Centre [ACCDC]). The adventive occurrence near St. Thomas (SP-X) was excluded from all calculations.

Current EOO: Extent of occurrence (EOO) within Canada is 103,766 km², calculated using a minimum convex polygon that encompasses all reported subpopulations from 2003 to 2022, all of which are considered extant. This calculation includes land and water area in the United States but does not include records from the United States range (Figure 3). It is plausible that the actual EOO could be somewhat larger (for example, approximately 200,000 km²) if the species occurs in southern New Brunswick or elsewhere in southern Nova Scotia, Ontario or Quebec.

Current IAO: Index of area of occupancy (IAO) within Canada is 52 km², calculated using a 2 km x 2 km grid drawn over all reported subpopulations from 2003 to 2022, all of which are extant. The actual IAO is unlikely to be larger than 100 km², as few additional sites are likely to be found in Canada.

Fluctuations and trends in distribution

There is no evidence that the actual distribution, EOO or IAO, has fluctuated. Loss of the two extirpated subpopulations in Quebec (SP# 1 and #2) resulted in a 12.5% decrease in the known EOO, from 118,613 km² to 103,766 km², and a 13% decrease in the known IAO, from 60 km² to 52 km². The timing of these decreases is unknown, as these subpopulations were last reported in 1920 and 1952. The extirpation of the adventive subpopulation near St. Thomas, Ontario (SP-X) occurred sometime after 1990.

Knowledge of the distribution of Forked Bluecurls in Canada has increased over time, particularly between 2003 and 2013, when seven of the eleven subpopulations (SP#4 to 10) were first reported, and it is unlikely that this represents a true increase in IAO. Most of these subpopulations are situated on private land, which may account for the paucity of historical records. The known distribution in Canada has not changed significantly over the past 10 years, as the only subpopulation (SP#11, Ungers Corners North, Ontario) found during this period is near other known subpopulations.

Biology and habitat use

Life cycle and reproduction

Forked Bluecurls is an annual plant that completes its life cycle in a single growing season. In Connecticut, seed germination occurs in late April, followed by an extended period of root development prior to the growth of the above-ground branching plant structure over the summer months (Olmsted 1937). Timing of germination may be later in the northern range, as plants are not obvious until July (MNFI 2022).

In Ontario, flowering begins in late July, peaks in mid-August, and tapers off by early September. Flower phenology in Quebec and Nova Scotia follows a similar schedule. Fruit maturation and dispersal occurs in late August through September. Dead plants may remain erect and identifiable until snowfall.

The number of flowers per plant varies with plant size, ranging from fewer than ten to more than 250 (Heagy pers. obs. 2022). Each flower is capable of producing four nutlets, each of which contains one seed. The flower structure of Forked Bluecurls is analogous to that of cross-pollinating Trichostema species found in California (Spira 1980). A high rate of seed set was observed at sites in Ontario in 2021 and 2022, with most flowers producing two or more nutlets (Heagy pers. obs. 2022).

Seed germination in this species is high under suitable conditions, and self-seeding in native plant gardens has been described as “prolific” (Vogelpohl 2015). In a germination experiment, most seeds germinated in the first year and some in the second year, but germination rates plummeted after the third year (McClelland pers. comm. 2022). Seed germination and dormancy has been studied in the two other annual Trichostema species found in eastern North America. Seed germination in Narrow-leaved Bluecurls (T. setaceum) increased when exposed to light, but light was not essential (Deno 1993). Germination rates of Fluxweed increased substantially in the second and third springs after dispersal when exposed to both cold (winter) stratification and warm (summer) stratification treatments, while germination rates of seeds exposed only to winter stratification remained low (Baskin and Baskin 2022). Germination of Forked Bluecurls seeds requires a period of cold stratification (McClelland pers. comm. 2022). In northern climes, the species may also require or benefit from a period of warm stratification (after-ripening) to break dormancy, a pattern that could delay the germination of late-maturing fruit by a full year. The generation time is estimated to be three years, given the species’ annual life cycle and estimated germination period of less than two years for most seeds.

High rates of seedling mortality were observed at a sand barren site in Connecticut under severe drought conditions (Olmstead 1937). The portion of plants that perish before maturing likely varies considerably by site and year, and is greatest at sites with high off-road vehicle (ORV) traffic or very dry soils. Seed banking is critical to annual species in years with poor survival to flowering or seed set (O’Connor 2007). Seed longevity has not been studied but, if conditions are unfavourable for germination (for example, heavy shade), viable seeds may persist as a seed bank for many years. At one site in Ontario (3B), plants appeared spontaneously following the removal of a dense stand of pine trees that were more than 30 years old (Heagy pers. obs. 2022). However, the possibility that the seeds were introduced by the heavy equipment used to remove the trees at this site cannot be ruled out.

Habitat requirements

Across its range, Forked Bluecurls is found in a variety of natural habitats, including barrens, rock outcrops, prairies and open woods. It also occurs in anthropogenically disturbed open habitats such as sandy fields, roadsides and railway embankments (O’Connor 2007; NatureServe 2022; Figures 4 and 5).

In its core range in the United States, this species tends to be a generalist and can tolerate a wide range of soil moisture and pH conditions, but prefers full to partial sun (McClelland pers. comm. 2022). In the northern part of its range, including the Canadian portion, its habitat requirements are more restrictive, and Forked Bluecurls is typically found only in sparsely vegetated open areas on acidic, dry to mesic, sandy or gravelly mineral soils. There are regional differences in habitat across the Canadian population.

The three subpopulations in Ontario (SP#3, #4 and #11; Figure 3) are clustered on part of the Norfolk Sand Plain, a 313,000-ha area of post-glacial sand deposits (Chapman and Putnam 1984). Four extant subpopulations in Quebec (SP#6, #7, #9 and #10; Figure 3) are situated on a 12,000-ha area of post-glacial sand deposits referred to as the Cazaville Dunes. In both these regions, Forked Bluecurls subpopulations are closely associated with anthropogenic features, including linear features such as forest access roads, off-road recreational vehicle (ORV) trails or powerline rights-of-way and open features such as sandpits and old fields.

The Saint-Chrysostome West subpopulation in Quebec (SP#8) occurs in sandy and gravelly soil in a horse paddock. The Saint-Chrysostome West site is adjacent to a sandstone barren that supports several rare species; however, botanical surveys of that habitat did not find any Forked Bluecurls (NCC 2014). This species has not been reported in alvar habitats in Ontario or Quebec. The two extirpated subpopulations in Quebec appear to have been situated in active shoreline settings, including a small islet in the Lachine Rapids in the St. Lawrence River (SP#1) and the sandy shoreline of Missisquoi Bay on Lake Champlain (SP#2).

In the extant subpopulations in Ontario and Quebec, Forked Bluecurls occurs in areas of loose, exposed sand with sparse vegetation and high light availability. These sandy soils typically have low levels of organic matter and nutrients and often experience moisture deficits during the growing season. These subpopulations currently occur in a landscape that is generally a mosaic of agricultural fields, mixed forests and pine plantations. Historically, in the case of the Ontario subpopulations, Forked Bluecurls habitat would have occurred as sand barren inclusions in oak savannahs or oak-pine woodlands (Draper et al. 2002) and, for the Quebec subpopulations, in Eastern White Pine (Pinus strobus) woodlands (Brisson and Bouchard 2003; Barbeau and Brisson 2004), which were maintained in an open condition by periodic wildfires and/or the cultural use of fire by Indigenous peoples.

The plants at the Shingle Lake site (SP#5, Figure 5) in Nova Scotia are in pockets of shallow soil in a naturally open sandstone rock barren in a pine-dominated forest. The nutrient-poor soils and very dry to dry moisture regime limits competition from other vegetation (Porter et al. 2020). Similar rock barren habitat is locally distributed over a large area in southern Nova Scotia (Farrow and Nussey 2017; Porter et al. 2020), and additional subpopulations may be present in remote areas.

While this species can tolerate partial sun, plants growing in shaded habitat are smaller and less productive than those in full sun (NCC 2014; Heagy pers. obs. 2022). Moisture-stressed plants also tend to be smaller and less productive. In the absence of fire, an anthropogenic disturbance regime is critical to the survival of this species at all sites in Ontario and Quebec. Excessive disturbance (for example, from intensive ORV traffic or sand extraction) can result in the loss of many or all of the affected plants but, without some disturbance, other vegetation rapidly colonizes these open areas, rendering them unsuitable for Forked Bluecurls.

Associated species differ regionally and by site and include some rare plants, including species listed under the Species at Risk Act, as well as various common sun-loving, drought- or disturbance-tolerant species. Spotted Wintergreen (Chimaphila maculata, Threatened) and Virginia Goat’s-rue (Tephrosia virginiana, Endangered) occur in proximity to Forked Bluecurls in the Turkey Point, Ontario, subpopulation (SP#3, Figure 4). Forked Three-awned Grass (Aristida basiramea, Endangered) and the nationally rare Spotted Beebalm (Monarda punctata, N1N2) occur in proximity to Forked Bluecurls at some sites in the Cazaville area of Quebec. The Nova Scotia subpopulation of Forked Bluecurls is one of 55 nationally rare taxa included in the Atlantic Coastal Plain Flora of Atlantic Canada (ECCC 2022).

Dispersal

Seed dispersal has not been studied in this species. The fruit develops in an open cup-like structure formed by the rotated calyx; this provides a springboard mechanism that, when depressed by a raindrop or brushed by an organism, catapults the fruit a short distance (a few metres) away from the plant (Brodie 1955; McClelland pers. comm. 2022). The smooth nutlets do not have any specialized dispersal mechanism, but wind dispersal may be significant in open barren habitat (Olmsted 1937). Birds could potentially disperse the seeds over longer distances, but this is considered a very rare circumstance (Townsend 1906; McClelland pers. comm. 2022).

Many sites in Ontario and Quebec are situated along ORV trails, and seeds could be spread by vehicle tires or trail maintenance equipment. However, this type of assisted dispersal appears to occur infrequently, as many areas of suitable habitat along trails are not occupied by the species. At the locale of the Turkey Point subpopulation (SP#3, Figure 4), the species’ patch distribution along the extensive network of trails used by recreational vehicles has been consistent since at least 2001. Similarly, at a site (4A) where the species is present on regularly mowed trails, the species’ patch distribution has not changed noticeably over the past ten years, even when apparently suitable habitat is present elsewhere on the trail network (Heagy pers. obs. 2022). Seeds transported in sand, hay or other material may give rise to adventive subpopulations associated with railways (for example, SP-X, Figure 3).

Interspecific interactions

Pollination

Forked Bluecurls is insect-pollinated, although self-pollination can occur (McClelland pers. comm. 2022). Details on pollinator species are not available, but the flower structure suggests that mid-sized bees are likely important pollinators.

Competitors

This sun-loving annual herb is not able to compete or co-exist with dense vegetation.

Seed dispersal

Birds are known to consume the seeds (Townsend 1906), and could potentially disperse seeds (McClelland pers. comm. 2022)

Other interactions

The larvae of a cosmet moth, Stagmatophora sexnotella, feed on Forked Bluecurls and other Trichostema species, resulting in distinctive stem galls (VanDyk 2022). These galls have been observed on Fluxweed in Ontario (iNaturalist 2023) and on Forked Bluecurls in northern Ohio, less than 100 km south of the Ontario plant subpopulations.

Physiological, behavioural, and other adaptations

The long taproot of this drought-tolerant species, which can sometimes exceed the stem in length, is an adaptation for seeking soil moisture in dry environments (Olmsted 1937; Sabourin and Bélair 2014). This species is fire tolerant but is not fire dependent. It benefits from natural or anthropogenic disturbances that expose mineral soils, reduce ground cover and maintain an open canopy, provided that the extent of the disturbance does not result in the complete loss of the seed bank or excessive plant mortality. Under ideal conditions, it can produce large numbers of seeds that can persist as a seed bank for several years. It is easy to propagate from seed.

Limiting factors

Limiting factors are generally not human-induced and include intrinsic characteristics that make the species less likely to respond to conservation efforts. Limiting factors may become threats if they result in population decline. The main limiting factors for Forked Bluecurls in Canada appear to be its specific habitat requirements: high light levels and dry, loose, acidic, sandy or gravelly mineral soils, which are needed for seeds to germinate and thrive, and its inability to compete with dense ground cover or under shade-casting vegetation. In the northern part of its global range, it is also presumably limited by the length of the growing season or other climatic conditions.

Population sizes and trends

Data sources, methodologies, and uncertainties

Information on Forked Bluecurls in Canada was obtained from sources including published articles on the occurrence of the species in Ontario (Montgomery and Morton 1973) and Quebec (Sabourin and Bélair 2014), conservation data centres in its Canadian range (ACCDC 2022; CDPNQ 2022; ONHIC 2022), online databases (Canadensys 2021; GBIF 2022; iNaturalist 2022), unpublished reports and data (Oldham 2018; NCC 2014, 2022), and other communications provided by land managers, biologists and naturalists (see Information Sources and Acknowledgements). Field verification surveys were conducted at known sites in Ontario in preparation for this report, but no targeted surveys were conducted elsewhere, as recent data were available for most extant Quebec and Nova Scotia subpopulations. For most extant sites, the available information consists of accurate geographic coordinates, and visual estimates or counts of the number of individual plants present, along with some information on patch size, habitat, associated species and/or threats.

Appendix 1 contains a compilation of all available abundance information for each subpopulation and site. The abundance information used to develop the current population estimate and infer short-term (10-year) trends is compiled in Table 2. Data sources and limitations vary by region, subpopulation and site, as discussed below.

Available information for the Turkey Point subpopulation (SP#3) includes several abundance estimates by various biologists over the past 50 years during other fieldwork (Appendix 1). Little previous information is available for the other Ontario subpopulations (Table 2, Appendix 1). In August 2022, targeted surveys and detailed counts were conducted by Heagy at all known Forked Bluecurls sites at the Turkey Point (SP#3) and Ungers Corners East (SP#4) subpopulations. At the only known site in the Ungers Corners North subpopulation (SP#11), landowner permission was not obtained for fieldwork in 2022, but the presence of the species was visually confirmed from the adjacent property and a crude abundance estimate was made based on this observation and the amount of suitable habitat. A targeted search was also conducted at the railyard site near St. Thomas, Ontario (SP-X). All fieldwork in 2022 was conducted under optimal conditions for detecting this species (mornings with fair weather during the peak flowering period). Individual plants were marked with wire flags to obtain an accurate count of the number of mature individuals present. All counts were single-day counts except for at Site 4A, where plants were checked almost daily, and additional markers added, from the start of the flowering period in late July until September 4, when a cumulative count of all of the markers was performed. The targeted surveys in Ontario focused on confirming the species’ presence and collecting abundance data for the known sites, as numerous botanical surveys and life science inventories have been conducted in the vicinity of the Ontario subpopulations. Of the 40 hours of field effort in 2022, four hours were spent searching for accessible potential habitat (sandy openings, ORV trails and road edges) within a kilometre of the known subpopulations.

Distribution and abundance data for Forked Bluecurls in southwestern Quebec are available as a result of botanical surveys by the Nature Conservancy of Canada (NCC) targeting Forked Three-awned Grass occurrences and habitat (NCC 2014, 2022; Sabourin and Bélair 2014). Reconnaissance plant surveys by NCC staff between 2011 and 2013 targeted private properties in two physiographic regions in the MRC du Haut-Saint-Laurent [Haut-Saint-Laurent regional county municipality], including an area of sand dunes near Cazaville (Cazaville Dunes) and an area of sandstone outcroppings near Le Rocher (NCC 2014). During these surveys, Forked Bluecurls was discovered at five of the 15 properties surveyed in the Cazaville Dunes area and none of ten properties surveyed in the Le Rocher area. The five occupied properties in the Cazaville Dunes area correspond to two properties (Sites 6A and 6B) in the Cazaville South subpopulation (SP#6) and three other subpopulations: Route 132 South (SP#7), Chemin Neuf South (SP#9), and Chemin Ridge North (SP#10, includes three sites). NCC botanists have continued to document the five Forked Bluecurls sites in the Cazaville Dunes area when monitoring Forked Three-awned Grass occurrences and have found Forked Bluecurls at one additional property (Site 6C) in the Cazaville South subpopulation (SP#6) (Environment Canada 2014; NCC 2022). Forked Bluecurls count data collected by NCC is based on checking all known patches in these four subpopulations (SP#6, 7, 9 and 10) in 2020 to 2022 (Table 2) and used similar methodology to the 2011 to 2013 surveys (Tanguay pers. comm. 2022).

The other extant subpopulation in Quebec, Saint-Chrysostome West (SP#8), is situated immediately south of the Le Rocher sandstone outcropping. The only information on this subpopulation comes from the 2013 iNaturalist record, which includes an abundance estimate of 40 to 50 plants (Table 2, Appendix 1). Abundance information is not available for the two extirpated Quebec subpopulations (SP#1 and 2).

The only Nova Scotia subpopulation, Shingle Lake (SP#5, Figure 5), was well documented upon its discovery by S. Blaney in August 2011. This site has been visited occasionally since 2011 by biologists and naturalists (Appendix 1). Abundance information from 2018 is available for both the main patch and a separate opening (Table 2).

Individual plants of this annual species can be readily discerned and counted, and observations at the Ontario sites (4A) indicate that even very small plants detected during the flowering period will generally produce some flowers and are therefore capable of reproducing (Heagy pers. obs.). Therefore, the number of plants observed after August 1 is equivalent to the number of mature individuals detected. Early season (July) counts include seedlings that may not survive to maturity.

Detectability is imperfect and varies by site (higher at sites with bare soils than at those with more vegetation), time of day (flowers open in the morning and drop to the ground by mid-day), date (drops off after the peak flowering period) and year (timing of senescence is affected by drought conditions and early/late frosts). According to the results of the cumulative count at Site 4A in 2022, single-day counts may underestimate the actual population by up to 50% in patches with moderate vegetation cover (~ 30% exposed sand). Most preliminary counts carried out by Heagy at the Ungers Corners East (SP#4, sites 4A and 4B) and Turkey Point (SP#3, sites 3A, 3B, 3C and 3D) subpopulations in late September 2021 after most plants had senesced were 50 to 80% lower than counts at the same sites in August 2022, and very small patches were not detected (Appendix 1). The accuracy of most abundance estimates is uncertain and likely varies considerably by observer. Known sites where the species was not detected during the most recent surveys (for example, 10A, 10C) are considered extant, as seed bank assessments are not available for this species and seed longevity is uncertain but likely several years.

Despite these limitations and uncertainties, the information available is considered sufficient for developing minimum abundance estimates for most known sites and the overall population, and with caution can be used to infer short-term general population trends for some sites and the overall population (Table 2).

Abundance

The total population of Forked Bluecurls at the nine extant subpopulations in Canada in 2022 is estimated to be in the range of 3,200 to 3,700 mature individuals (Table 2). These subpopulations likely make up most of the overall population, given the extent of past survey efforts.

Available quantitative information on abundance (counts or visual estimates) for two periods, 2020 to 2022 (current) and 2010 to 2013 (past), at each of the 16 sites of the nine extant subpopulations is summarized in Table 2. The most recent abundance information for the Shingle Lake, Nova Scotia, subpopulation (SP#5) was collected in 2018. Current information is not available for the single site (8A) in the Saint-Chrysostome West subpopulation. Past abundance information is not available for five sites (3B, 3C, 4B, 11A and 6C). The information in Table 2 was used to develop current and past abundance estimates for each site (or sub-site) and subpopulation. Site abundance estimates are given as a single number if the available information was provided as a single number (108 plants, ~ 400 plants), or as a range if provided as a range (40 to 50 plants), a minimum value (more than 150 plants = > 150) or an approximation (thousands of plants = 2,000 to 3,000). For each subpopulation, the site abundance estimates were summed and then rounded to an appropriate number of significant digits, given the uncertainty (Table 2). Where adequate information to make a comparison was not available for a site or sub-site, the abundance was assumed to be unchanged and the best available estimate for the site was used to evaluate the subpopulation size. The site and subpopulation abundance estimates in Table 2 are conservative (lower plausible limit), as the count data have not been adjusted for imperfect detectability.

Fluctuations and trends

Caution must be used in comparing and interpreting past and present site-level abundance estimates, as they are based on limited data (see Data Sources, Methodologies, and Uncertainty and the Notes column in Table 2) and the assumption that abundance was unchanged unless there was evidence of an observed change.

Continuing decline^{Footnote 6} in number of mature individuals

A continuing decline is observed, although recent declines at some sites (see below) appear to have been driven largely by site-specific changes in disturbance regimes and habitat conditions, and it is not known whether habitat-related declines at privately owned sites are ongoing or have ceased, or are potentially reversible for subpopulations (SP#3 and #7) in protected areas where beneficial habitat management is in progress or planned. Forked Bluecurls could potentially benefit from climate change (see Threats and Appendix 2).

Evidence for past decline (3 generations or 10 years, whichever is longer) that has either ceased or is continuing (specify)

There has been an observed decline in the overall Forked Bluecurls population over the past 10 years, as there is evidence of large decreases at four subpopulations and a suspected moderate increase at only one subpopulation.

Abundance information collected by NCC staff since 2011 using consistent survey methods and timing at a number of sites in the four subpopulations (SP#6, #7, #9 and #10) in the Cazaville Dunes area in Quebec documented a substantial reduction in the size of these subpopulations (Table 2). Among the seven Cazaville Dunes sites for which abundance data from both periods were available, two sites (10A and 10C) saw a complete disappearance of mature individuals, three sites (6B, 7A and 9A) had a decline of one order of magnitude, one site (10B) had a moderate decline, and one site (6A) had stable numbers. Over 6,000 plants were observed at the seven sites during the surveys conducted in 2011 to 2013, while fewer than 1,000 plants were found during follow-up surveys in 2020 to 2022 (NCC 2014, 2022; Sabourin and Bélair 2014). Similar large reductions in the abundance of Forked Three-awned Grass and Spotted Beebalm were also observed at several of these sites (Tanguay pers. comm. 2022). There is no information on population trends for the other Quebec subpopulation, Saint-Chrysostome West (SP#8).

At Site 10A, most of the plants observed in 2011 occurred on an abandoned horse training track, and the disappearance of the plants from the track is related to a change in the substrate due to the disintegration of the geotextile fabric on the track (Tanguay pers. comm. 2023). Factors behind the observed declines at Sites 6B and 9A are not well understood, but may be related to decreased disturbance and associated habitat changes, including increased competition from invasive and native plants. The cause of the substantial decline at Site 7A is not known, as no noticeable change occurred in the habitat or land use between 2012 and 2013 (Tanguay pers. comm. 2022). Active habitat management (removal of Red Pine plantations) to improve habitat for Forked Bluecurls and other rare plants is scheduled to take place at Site 7A within the next 5 years and has the potential to result in a rapid population increase.

Of the six sites (nine sub-sites) in the three subpopulations in Ontario, past abundance estimates are available for only one site (Site 3A). The past survey effort at 3A (which has two sub-sites) since 1971 is not comparable to the more comprehensive targeted surveys done in 2022, but there is no indication of a long-term population decline at that site (Table 2, Appendix 1). The small (~ 25%) increase in the Turkey Point subpopulation (SP#3) is attributed to recent habitat management efforts at Site 3B, with 260 plants observed in 2022 in an area (sub-site 3 B-E) where no plants were observed during pre-management surveys in 2019. The 33 plants at the seed trial sub-site (3C-S) are not included in the population estimates, as it is not known whether this manipulated subpopulation will persist.

There is no evidence to suggest that the abundance of either of the other two Ontario subpopulations, Ungers Corners East (SP#4) and Ungers Corners North (SP#11), has changed over the past 10 years. The Shingle Lake subpopulation (SP#5) in Nova Scotia appears to have been stable between 2011 (when it was discovered) and 2018 (Table 2).

On the basis of the information and assumptions used to develop the subpopulation abundance estimates (Table 2), there is an inferred reduction in the known Canadian population of Forked Bluecurls of at least 50% (> 5,000 mature individuals) over the past 10 years.

Factors contributing to the recent declines are not fully understood. It is uncertain if the decline has ceased, since the disturbance regime at privately owned sites is subject to change. Habitat management at the Turkey Point, Ontario (SP#3) and Route 132 South, Quebec (SP#7) subpopulations could result in a rapid population increase.

Evidence for projected or suspected future decline (next 3 generations or 10 years, whichever is longer, up to a maximum of 100 years)

Habitat trends are unknown, and the response to habitat management is uncertain.

Long-term trends

Unknown. Long-term population trends for this species are poorly understood, as most subpopulations were found relatively recently. The longer term abundance information available suggests that the size of the Turkey Point (SP#3) and Ungers Corners East (SP#4) subpopulations has been relatively stable since they were first reported in 1971 and 2003, respectively. There is no information on the extirpated subpopulations near La Prairie (SP#1) and Missisquoi Bay (SP#2), which are known exclusively from herbarium specimens collected in 1920 and 1952, respectively.

Population fluctuations, including extreme fluctuations

There is no indication that extreme natural population fluctuations occur. Forked Bluecurls is an annual plant, and the number of mature individuals is expected to vary from year to year in response to variations in environmental conditions affecting germination and survival to maturity.

Severe fragmentation

The population is not considered severely fragmented. The minimal viable subpopulation and expected dispersal distances are unknown, but the species appears to be able to persist in small, scattered habitat patches of less than 1 ha in area.

Rescue effect

The known Forked Bluecurls subpopulations in Ontario and Nova Scotia are separated from the nearest subpopulations in the United States by large water bodies (Figures 2 and 3). The Quebec subpopulations are close to subpopulations in eastern New York and western Vermont near the Canada-U.S. border. In New York, where the species is considered Secure (S5) and stable, it is broadly distributed in the eastern half of the state, including counties adjacent to southeastern Ontario and southwestern Quebec (NatureServe 2022; Ring pers. comm. 2023). In Vermont, the species is not uncommon and apparently stable (Popp pers. comm. 2023). In Michigan, Forked Bluecurls is an Imperiled (S2) species that persists in disturbed areas at sites that historically supported Black Oak sand savannah vegetation (Bassett pers. comm. 2023). It has not been reported from southeastern Michigan since 1916 (MNFI 2022). The status of this species in other states in the northern part of its U.S. range has not been assessed, but it is not a common species in Ohio, where its habitat is scattered and generally declining (Gardner pers. comm. 2023). Forked Bluecurls is widespread and apparently secure in New Hampshire, where much of its natural habitat has been lost, but the species persists along roads and other anthropogenically disturbed habitats (Nichols pers. comm. 2023), and is uncommon but apparently stable in Maine (Cameron pers. comm. 2023).

The extirpated occurrence at a former railyard near St. Thomas, Ontario (SP-X) was presumably introduced through seeds transported by rail from the United States, in view of the large U.S. and tiny Canadian subpopulations of the species and its separation from other Canadian subpopulations. Given the extensive network of cross-border transportation corridors in this region of Canada, other human-assisted introduction events will likely occur occasionally in southern Ontario and southern Quebec, but rescue is not considered a major factor mitigating the conservation concern for the native Canadian population.

Threats

Historical, long-term, and continuing habitat trends

The habitats in this species’ range in Ontario and Quebec have been strongly influenced by thousands of years of human occupancy. The use of fire by Indigenous peoples was likely beneficial in maintaining the open habitat required by this species. The clearing of forest cover by European settlers may have also been beneficial, but the subsequent conversion of most land in these regions to agricultural fields in the 1800s was likely detrimental. The landscape near the Ontario and Quebec subpopulations continues to be dominated by agriculture, but with a significant amount of forest cover (including naturally regenerated forests and plantations) on dry, erosion-prone sandy soils. Natural ecosystem processes in these regions, such as periodic wildfires and predator-prey relationships, are often disrupted. Private and public lands in these regions—including protected areas—generally experience intense use. The current distribution of Forked Bluecurls in these regions is confined to areas with dry, sandy soils subject to anthropogenic disturbances that create and maintain open habitat, as described in the Habitat requirements section. Ongoing habitat suitability is dependent on the maintenance of an appropriate disturbance regime.

In contrast, the single subpopulation in Nova Scotia occurs in a naturally open situation that is not dependent on anthropogenic disturbances and faces few immediate threats compared to the subpopulations in Ontario and Quebec.

Current and projected future threats

Forked Bluecurls is vulnerable to the cumulative effects of various threats, especially threats that result in habitat succession. The nature, scope and severity of these threats are described in Appendix 2, following the IUCN-CMP (International Union for the Conservation of Nature – Conservation Measures Partnership) unified threats classification system (see Salafsky et al. 2008 for definitions and Master et al. 2012 for guidelines). The threat assessment process consists of assessing 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 within the scope during the next 10 years or 3 generations, whichever is longer up to ~100 years) and timing of each threat. The overall threat impact is calculated by taking into account the separate impacts of all threat categories, and can be adjusted by the species experts participating in the threats evaluation.

The overall threat impact for Forked Bluecurls is considered to be Medium to Low, corresponding to an anticipated further decline of 1 to 30% over the next ten years. These values are to be interpreted with caution, as they may be based on subjective information such as expert opinion, although efforts have been made to corroborate the scores with available studies and quantitative data.

Natural system modifications (IUCN 7; overall threat impact medium - low)

The main threat to Forked Bluecurls in Canada is the general disruption of ecological processes (7.3 Other Ecosystem Modifications) at many sites in Ontario and Quebec. Habitat succession due to the absence of disturbance (including 7.1 Fire and Fire Suppression) is an ongoing threat to this species, which does not tolerate competition or shade. Habitat can quickly become unsuitable for Forked Bluecurls due to the rapid growth of native early successional plant species such as goldenrods (Solidago spp.), Trembling Aspen (Populus tremuloides) and Eastern White Pine, as well as invasive non-native species such as Kentucky Bluegrass (Poa pratensis), Sheep Sorrel (Rumex acetosella) and Scots Pine (Pinus sylvestris). Competition from other vegetation is the probable cause of the observed declines that have occurred at several sites in Quebec following changes to the disturbance regime (inactive sandpits at Site 6B and abandoned horse training track at Site 10A).

Agricultural and aquaculture (IUCN 2; overall threat impact unknown)

This threat category includes three activities, each of which poses a specific threat to Forked Bluecurls on private lands in Ontario and Quebec: conversion to annual non-timber crops (2.1), conversion to wood and pulp plantations (2.2), and livestock farming and ranching (2.3). This species often occurs on lands that are poorly suited to agriculture, but some sites (4A and 11A in Ontario, and 8A and 10A in Quebec) are on marginal agricultural land that could be converted to row crops, although this is not considered likely to occur at any of the known sites within the next 10 years. New timber plantations could potentially be established at these or other private sites, particularly in response to tree planting incentive programs, but this is also considered unlikely within the next 10 years. The ongoing growth of pine plantations at subpopulations SP#3 and SP#7 is resulting in increased shade, but these plantations are being actively managed to increase light availability. Livestock farming and ranching are occurring or could occur at several sites (4A in Ontario, and 8A and 10A in Quebec), but the impact of this threat is unknown, since grazing and soil disturbance from these activities could be beneficial, while over-seeding with forage crops would be detrimental.

Activities such as sand extraction (3.2), road and right-of-way maintenance (4.1 and 4.2), logging (5.3), and off-road recreational vehicle activities (6.1) are ongoing at several sites in Ontario and Quebec. These activities are not considered threats to the overall population, given that the resulting disturbance is considered beneficial in creating and maintaining suitable habitat. However, off-road recreational vehicle activity would be detrimental to the rock barren habitat at the Shingle Lake site (5A) in Nova Scotia.

Ongoing habitat modifications due to climate change are expected, but the impact on this species is unknown and potentially beneficial, as some plant hardiness modelling projections suggest that the climate envelope for this species in Canada could expand beyond the current range (NRC 2022).

Number of threat locations

The number of locations, where a single change in land use leading to a change in the disturbance regime could rapidly affect all individuals within a 10-year period, is at least 13, since the disturbance regime is determined primarily by the landowner or land manager and the 16 known sites involve about 13 different landowners/managers (Table 1). The number of distinct landowners at some sites is uncertain, but the number of locations is believed to be more than 10.

Protection, status, and recovery activities

Legal protection and status

Forked Bluecurls currently has no federal or provincial legal protection or status in Canada. In the United States, this species is legally protected as a Threatened species in Michigan (MNFI 2022).

Non-legal status and ranks

The global status of this species is ranked as Secure (G5, last reviewed in 2002; NatureServe 2022). In Canada, Forked Bluecurls is ranked as Critically Imperiled (N1, assessed 11 October 2022; NatureServe 2022).

At the provincial level, this species is ranked Critically Imperiled (S1) in Ontario (last assessed 31 December 2015; ONHIC 2022), Quebec (last assessed 2 March 2022; CDPNQ 2022) and Nova Scotia (last assessed 14 March 2022; ACCDC 2022).

In the northern United States, this species is ranked Possibly Extirpated (SH) in Iowa, Imperiled (S2) in Michigan, Vulnerable (S3) in Indiana and Secure (S5) in New York (NatureServe 2022). Subnational ranks have not been calculated (SNR) for Forked Bluecurls in Ohio, Pennsylvania, Vermont, New Hampshire or Maine, as the species is not rare and is likely Apparently Secure (S4) in most of those jurisdictions (see Rescue effect).

Land tenure and ownership

Two extant subpopulations, Turkey Point (SP#3) and Shingle Lake (SP#5), are in provincially protected areas and most or all the Route 132 South (SP#7) subpopulation in Quebec is in a voluntary protected area (Table 1). These three subpopulations currently account for approximately half the total population of Forked Bluecurls in Canada. The locales of the two extirpated subpopulations in Quebec (SP#1 and #2) may also fall within protected areas (see Table 1).

A few other sites are afforded some voluntary protection by current landowners. Site 6A is situated on a municipal lot and is protected by a conservation agreement (Tanguay pers. comm. 2023). Private landowners at sites 4A and 10A are interested in conserving rare plants (Heagy pers. obs.; Tanguay pers. comm. 2023).

The extant subpopulations of Forked Bluecurls in Canada are all situated within areas^{Footnote 7} identified as Priority Places for Species at Risk under the Pan-Canadian Approach to Transforming Species at Risk Conservation in Canada (ECCC 2022). Conservation organizations are actively targeting core areas in these priority places for protection and/or conservation management, including lands in the vicinity of the six extant Forked Bluecurls subpopulations on private lands in southwestern Ontario and southwestern Quebec.

Information sources

References cited

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Collections examined

No collections were examined for the preparation of this report.

Authorities contacted

• Bassett, T., Conservation Association – Botanist. Michigan Natural Features Inventory. Lansing, Michigan
• Belliveau, A. Botanist. E.C. Smith Herbarium, Acadia University. Wolfville, Nova Scotia
• Bickerton, H. Independent biologist. Ottawa, Ontario
• Brinker, S.R. Provincial Botanist. Ontario Natural Heritage Information Centre. Peterborough, Ontario
• Cameron, D.S. Botanist/Ecologist. Maine Natural Areas Program. Augusta, Maine
• Cloutier, C. Project Manager. Nature Conservancy of Canada. Montreal, Quebec
• Deacon, P. Biologist. Natural Resources Solutions Inc. Waterloo, Ontario
• Gardner, R. Chief Botanist. Department of Natural Resources. Columbus, Ohio
• Gartshore, M. Independent biologist and naturalist. Walsingham, Ontario
• McClelland, R.K.S. Lecturer in Biology. Elon University. Burlington, North Carolina, United States
• Nichols, W.F State Botanist. New Hampshire Natural Heritage Bureau, Division of Forests and Lands. Concord, New Hampshire
• Popp, B. Department Botanist. Vermont Department of Fish and Wildlife. Barre, Vermont
• Ring, R.M. Chief Botanist. New York Natural Heritage Program. Albany, New York
• Tanguay, C. Stewardship Coordinator. Nature Conservancy of Canada. Montreal, Quebec
• Van Hemessen, W. Independent consulting biologist. Cambridge, Ontario

Acknowledgements

Funding for the preparation of this report was provided by Environment and Climate Change Canada. The authorities listed above provided valuable data and/or advice. Bruce Bennett, Co-chair of the Vascular Plant Specialist Subcommittee (VPSSC), was most helpful in providing technical guidance and editorial comments throughout the drafting of this report. The report writer would like to thank all those who shared their expertise (see Authorities Contacted) and personal observations, especially Kevan McClelland, Caroline Tanguay, Alain Belliveau, Jacques Labrecque, Sean Blaney and Sam Brinker. Many reviewers contributed to improving this report, including Benoit Tremblay of the Quebec Ministère de l’Environnement, de la Lutte contre les changements climatiques, de la Faune et des Parcs (MELCCFP); Syd Cannings, Gina Schalk, Holly Bickerton, Marie Archambault, Julie McKnight, Eric Snyder, Rebecca Sutherland, Lingfei Li, and Karolyne Pickett of Environment and Climate Change Canada (ECCC); and Varina Crisfield, Sam Brinker, and Sean Blaney of the VPSSC. Del Meidinger, Sam Brinker, Caroline Tanguay (Nature Conservancy of Canada), Patricia Desilets (ECCC), Benoit Tremblay, Varina Crisfield, Claire Wilson O'Driscoll (Canadian Food Inspection Agency), Alyssa Pogson, Lingfei Li, Sean Blaney and Holly Bickerton assisted with the threats assessment call. David Okines assisted with the fieldwork for this report.

Biographical summary of report writer(s)

Audrey Heagy is a field biologist, technical writer and conservation practitioner with over 30 years experience working for non-profit conservation organizations and as an independent consultant, primarily in southern Ontario. She was the lead writer for the COSEWIC status report on three yellow false foxglove species (Aureolaria spp.), and an update status report on the Eastern False Rue-anemone (Enemion biternatum), as well as five other COSEWIC reports on bird and insect species. She is familiar with Forked Bluecurls occurrences in Ontario. She has extensive experience in planning, implementing, and reporting on species at risk surveys and habitat management in southern Ontario, particularly at the St. Williams Conservation Reserve.

Appendix 1. Compilation of available information on forked bluecurls subpopulations (SP) and sites in Canada

Appendix 2. Threats assessment for Forked Bluecurls

Threats assessment worksheet

Species or Ecosystem scientific name

Forked Bluecurls (Trichostema dichotomum)

Element ID

240005

Elcode

PDLAM22040

Date:

1/19/2023

Assessor(s):

Bruce Bennett, Del Meidinger, Audrey Heagy, Sam Brinker, Caroline Tanguay, Patricia Desilets, Benoit Tremblay, Varina Crisfield, Claire Wilson O'Driscoll, Alyssa Pogson, Lingfei Li, Sean Blaney, Holly Bickerton

Assigned overall threat impact:

CD = Medium - Low

Overall, threat comments :

Generation time 3 years (annual plus 2 years); most seeds germinate in the first 2 years. Seed bank slightly longer, so generation time may be slightly more than 3 years; 3 generations about 9 to 12 years.

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