Roell’s Brotherella Moss (Brotherella roellii): COSEWIC assessment and status report 2025

Official title: COSEWIC assessment and status report on the Roell’s Brotherella Moss (Brotherella roellii) in Canada

Endangered

2025

COSEWIC assessment summary

Assessment summary – May 2025

Common name: Roell’s Brotherella Moss

Scientific name: Brotherella roellii

Status: Endangered

Reason for designation: This moss is endemic to western North America, where all known existing subpopulations occur in the densely populated south-western mainland of British Columbia. Extensive sampling within and beyond this region has shown this species occurs only on hardwoods and rotten logs in riparian stands mostly within urban areas. At least 106 individuals have been identified from 30 known subpopulations. The species’ life history characteristics increase the vulnerability of the small subpopulations to loss from climate change associated with storms and droughts, as well as recreational use, road construction, and urban development, all of which also threaten habitat quantity and quality in terms of moisture levels and air quality.

Occurrence: British Columbia

Status history: Designated Endangered in November 2010. Status re-examined and confirmed in May 2025.

COSEWIC executive summary

Roell’s Brotherella Moss

Brotherella roellii

Wildlife species description and significance

Roell’s Brotherella Moss (Brotherella roellii) is a shiny, yellow to golden-green moss that forms turf-like mats. The leafy shoots are small, about 0.5 mm wide, and somewhat flattened. The species reproduces sexually by spores and also reproduces asexually by deciduous flagelliform shoots. Roell’s Brotherella Moss is endemic to the central Pacific coast of North America and the subpopulations in British Columbia likely represent the only extant sites in the world.

Aboriginal (Indigenous) knowledge

All species are significant and are interconnected and interrelated. There is no species-specific Aboriginal Traditional Knowledge (ATK) in the report.

Distribution

Globally, Roell’s Brotherella Moss is known only from southwestern British Columbia and Washington State. Roell’s Brotherella Moss is currently known from the Lower Mainland of British Columbia, in the Fraser River Valley and Howe Sound areas, spanning the region between the municipalities of Hope and Squamish. In the United States, there are only six unconfirmed subpopulations in Washington State. However, with the most recent report dating from over a century ago, Roell’s Brotherella Moss was ranked as SH (possibly extirpated) in the United States by NatureServe in 2022. Thus, all extant subpopulations are found in Canada.

Habitat

In Canada, Roell’s Brotherella Moss grows on trees, logs, stumps, and woody debris in cool and humid mixed broadleaf and coniferous forests, including second growth, on stream terraces, swampy flood plains, and occasionally in ravines with creeks. The primary substrates include the base of hardwoods and rotten wood. Many of the current sites occur within municipal, regional, and provincial parks in urban areas.

Biology

Roell’s Brotherella Moss is autoicous, having both male and female reproductive organs on the same plant. This increases the chance for successful fertilization and production of sporophytes. Sporophytes of Roell’s Brotherella Moss mature and disperse spores in the winter. The spore size is 13 to 17 µm, making regional dispersal likely over extended time periods (that is, multiple generations). Roell’s Brotherella Moss also produces deciduous flagelliform shoots; therefore, asexual reproduction, which tends to disperse locally, also occurs.

The life strategy of Roell’s Brotherella Moss is characterized by relatively common sexual and asexual reproduction and growth on substrates that disappear predictably after a certain period (for example, tree trunks, stumps, logs, and woody debris). Based on current IUCN guidelines for bryophytes, Roell’s Brotherella moss is considered a long-lived species with a generation length of 11 to 25 years.

The adaptability of Roell’s Brotherella Moss is unknown. Because Roell’s Brotherella Moss is restricted to humid mixed deciduous woodland, flood plains, and ravines, survival in sites of low humidity is unlikely, even if an appropriate substrate exists.

Population sizes and trends

The population size of Roell’s Brotherella Moss is calculated using subpopulations as we do not have accurate counts of individuals in subpopulations over time. Today, the Canadian population of Roell’s Brotherella Moss is currently known from 30 extant subpopulations, 12 that are geographically unconfirmed (geographic information from these subpopulations is not precise enough to permit their re-evaluation) and 4 that are believed to be extirpated. Another six subpopulations are considered extirpated. The estimated number of individuals (colonies) based on the most recent IUCN guidelines for the “individual-equivalent” for bryophytes is at least 106. Since the previous status assessment, 20 new subpopulations have been discovered. Not including the geographically unconfirmed subpopulations, there has been a continuing decline of 14.2% in the number of subpopulations in 12 years which is close to one generation (11 to 25).

Threats

The most significant threats to Roell’s Brotherella Moss include damage to individual-equivalents and habitat degradation. They are (1) climate change mediated storms that trigger flooding and geological events such as landslides; (2) invasive and other problematic species; (3) residential and commercial development, in particular, the expansion of housing for urban areas; and (4) human intrusion on habitat, predominantly with degradation of habitat due to recreational trail use. Rescue from the population in Washington State is very unlikely as that population is thought to be extirpated.

Protection, status, and recovery activities

Roell’s Brotherella Moss is listed as Endangered under the Species at Risk Act. The species is currently classified as G3 (Vulnerable) globally, N3? (Vulnerable) in Canada, and S1S2 (Critically Imperilled to Imperilled) in British Columbia and is on the provincial red list for species. Forty-three percent of the known extant and historic subpopulations are found in provincial, regional, or municipal parks.

Technical summary

Brotherella roellii

Roell’s Brotherella Moss

Dorure de Röll

Range of occurrence in Canada: British Columbia

Demographic information

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

Approximately 11 to 25 years

Based on Bergamini et al. (2019) system, adopted for IUCN European bryophyte red list (Hodgetts et al. 2019)

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

Yes, inferred past decline 14% over 12 years, with no reason to presume a stop in the decline

A decline in total number of mature individuals is inferred from the decline in the number of subpopulations since the last report (2010 to 2022). Subpopulations are used here to calculate decline as the exact number of individuals per subpopulation is unknown

[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

No observed, estimated, or projected decline, but inferred past decline of 14% over 12 years, which is within the variation of one generation time. Decline projected to continue due to continued threats

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, but inferred decline projected to continue due to continued threats

[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]

Yes, inferred decline of 7/37 = 18.9% subpopulations over the last 3 generations

A decline in total number of mature individuals is inferred from the decline in the number of subpopulations since the last report (2010 to 2022)

[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]

Inferred reduction in total number of individuals over the next 3 generations because of continuing threats

[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)

Inferred decline of 7/37 = 18.9% subpopulations over the last 3 generations

A decline in total number of mature individuals is inferred from the decline in the number of subpopulations since the last report (2010 to 2022)

Are the causes of the decline clearly reversible?

No

Climate change and development are unlikely to stop in the Lower Mainland region of British Columbia

Are the causes of the decline clearly understood?

Partially

Declines are due in part to development and recreation disturbing subpopulations in recreational areas and also due to climate change associated flooding in riverine habitat. The loss of some subpopulations cannot be explained and may be due to drought, or stochastic events.

Are the causes of the decline clearly ceased?

Unlikely

Climate change

Are there extreme fluctuations in number of mature individuals

No

Extent and occupancy information

Estimated extent of occurrence (EOO)

6,787 km²

Calculated based on minimum convex polygon around known extant sites from 2002 to 2022

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

128 km²

Based on known extant sites from 2002 to 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. Unknown

1. Habitat size required by Roell’s Brotherella Moss is small. A subpopulation can exist on a single tree, log, or piece of wood
2. Dispersal for this species has not been studied. The potential for dispersal among subpopulations is unknown. However, spores are 13 to 17 µm, making regional dispersal likely over generational time periods

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

>10

Residential development, recreational activity, and climate change threats occur throughout the species’ range. While some of these threats act simultaneously on all subpopulations, their manifestations, such as flooding or landslides for climate change, are unlikely to occur at all subpopulations at once

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

No

New subpopulations have been discovered since the previous status report, but they are within the past known extent of occurrence

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

No

New subpopulations have been discovered since the previous status report, but it is likely that these were previously existing but undocumented

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

Yes, inferred past decline of 14% between 2010 and 2022.

Inferred continuing decline in the future as threats have not stopped

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

Yes, based on the ensemble of threats, each subpopulation is a location, so an inferred past decline of 14%.

Inferred continuing decline in the future as threats have not stopped

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

Yes

Inferred continuing decline based on climate change, continuing residential development, and increasing human intrusions and recreation in the Lower Mainland region of British Columbia

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

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 (see Appendix 3)

Overall assigned threat impact: High – Medium (2023)

Key threats were identified as:

1. Climate Change and Severe Weather (IUCN 11) — Medium – Low impact
2. Invasive and Other Problematic Species and Genes (IUCN 8) — Medium – Low impact
3. Residential and Commercial Development (IUCN 1) — Low impact
4. Transportation and Service Corridors (IUCN 4) — Low impact
5. Biological Resource Use (IUCN 5) — Low impact
6. Human Intrusions and Disturbance (IUCN 6) — Low impact
7. Natural System Modifications (IUCN 7) — Low impact
8. Geological Events (IUCN 10) — Low impact

What limiting factors are relevant?

• Highly limited global range
• Strict niche requirements (high humidity and low light

Rescue effect (from outside Canada)

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

Unknown, likely extirpated

The U.S.A. population in Washington State is ranked SH (Possibly Extirpated; NatureServe 2022)

Is immigration known or possible?

Unlikely

Unlikely, as the U.S.A. population is thought to be extirpated

Would immigrants be adapted to survive in Canada?

Yes

Both populations have sites close to the U.S.A./Canada border. Environmental conditions are presumably similar enough to allow immigrants from the U.S.A. to survive in Canada

Is there sufficient habitat for immigrants in Canada?

Yes

Suitable habitat exists if immigrants could disperse to it

Are conditions deteriorating in Canada?

Yes

Habitat destruction due to residential development and habitat degradation from recreational activity and climate change are deteriorating conditions in Canada. See Threats.

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

Unknown

The U.S.A. population is possibly extirpated (COSEWIC 2010; NatureServe 2022)

Is the Canadian population considered to be a sink?

No

The Canadian population is likely the only extant population

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

No

The U.S.A. population is possibly extirpated

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

The British Columbia Conservation Data Centre does not consider species at risk data for Roell’s Brotherella Moss to be sensitive. Occurrence data are available to the public

Status

COSEWIC status history

Designated Endangered in November 2010. Status re-examined and confirmed in May 2025.

Status and reasons for designation

Status: Endangered

Alpha-numeric codes: C2a(i); D1

Reason for change in status: Not applicable

Reasons for designation: This moss is endemic to western North America, where all known existing subpopulations occur in the densely populated south-western mainland of British Columbia. Extensive sampling within and beyond this region has shown this species occurs only on hardwoods and rotten logs in riparian stands mostly within urban areas. At least 106 individuals have been identified from 30 known subpopulations. The species’ life history characteristics increase the vulnerability of the small subpopulations to loss from climate change associated storms and droughts, as well as recreational use, road construction, and urban development, all of which also threaten habitat quantity and quality in terms of moisture levels and air quality.

Applicability of criteria

A: Decline in total number of mature individuals

Not applicable.

Insufficient data to reliably infer, project, or suspect population trends.

B: Small range and decline or fluctuation

Not applicable.

IAO (128 km²) is below the threshold for Endangered, but population is not severely fragmented, occurs at more than 10 locations, and does not experience extreme fluctuations.

C: Small and declining number of mature individuals

Meets Endangered, C2a(i).

Number of mature individuals is fewer than 2,500, with fewer than 250 individuals in any one subpopulation, and there is an inferred continuing decline.

D: Very small or restricted population

Meets Endangered, D1.

Number of mature individuals estimated to be fewer than 250.

E: Quantitative analysis

Not applicable.

Analysis not conducted.

If a species is proposed as Special Concern, Data Deficient, Extirpated or Extinct, list the applicable guidelines, examples, or other considerations from O&P Appendix E3.

Preface

Since the previous status assessment (COSEWIC 2010), 1 subpopulation has been extirpated, and 4 more are believed to be extirpated. However, due to increased search effort, 20 new subpopulations of Roell’s Brotherella Moss have been discovered. The new subpopulations expand slightly the known substrates and elevation range for the species, which includes woody debris, and broadleaf trees less than 130 m above sea level. All subpopulations continue to be threatened by climate change–associated floods and droughts, residential development, and recreational activity. Recovery activities since the previous assessment include the publication of the provincial Recovery Plan (2013) and the Federal Recovery Strategy (2021). Since the previous assessment, substantial field surveys have been undertaken for this species across its range in Canada.

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

(2025)

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)*

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)**

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

Data deficient (DD)***

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.

Wildlife species description and significance

Name and classification

Current classification

Class: Bryopsida

Order: Hypnales

Family: Sematophyllaceae

Genus: Brotherella

Species: Brotherella roellii (Renauld and Cardot) Fleisch.

Subspecies in Canada

None

Taxonomic changes since previous report (for reassessments)

None

Common names

English: Roell’s Brotherella Moss

French: dorure de Röll (previously brotherelle de Roell)

Indigenous (specify language): None

Bibliographic citation: Botanisches Centralblatt 44:423. 1890.

Type specimen: Enumclaw, Washington, Julius Röll, 435, 7 July 1888 (WB)

Synonyms and notes

Brotherella roellii is the currently accepted name for Roell’s Brotherella Moss. Some recent studies have suggested that B. roellii is a synonym of B. fauriei; however, further investigation invalidates this claim. Specifically, in 2015, the genus Brotherella was revised based on morphological characters (Jia and Tan 2015). In this treatment, Brotherella roellii was synonymized with B. fauriei (Besch. ex Cardot) Broth., a species known from East Asia. In the same treatment, Jia and Tan (2015) suggest all British Columbian B. roellii material represents Pylasiadelpha tenuirostris (Bruch and Schimp. ex Sull.) Buck, another species in the Sematophyllaceae with a present distribution in North America of only the eastern states and provinces. Upon further investigation, it was discovered that Jia and Tan (2015) only examined a single specimen of B. roellii from British Columbia (Jia pers. comm. 2022), which has been further examined by local taxonomic experts who refute the claim that it represents P. tenuirostris (McIntosh and Joya pers. comm. 2022). Jia (pers. comm. 2022) concluded that the synonymy with Brotherella fauriei was also invalid. The name B. roellii should take priority as it is the older name. In 2021, new molecular phylogenetic analysis and classification of the Sematophyllaceae included a specimen of B. fauriei from Asia (Han and Jia 2021); unfortunately, North American material of B. roellii was not included in this study so the relation of Roell’s Brotherella Moss to others in the genus remains unclear.

Description of wildlife species

Morphological description

Plants are large for a moss, yellow to golden green, growing in shiny turf-like mats (Figure 1A); leafy shoots small ca. 0.5 mm wide, somewhat flattened (not complanate); occasionally forming deciduous flagelliform shoots (Figure 1B): stem cortical cells large, up to 15 µm wide; stem leaves + falcate, secund, ovate-lanceolate, acuminate, concave, 0.8 to 1.2 mm x 0.2 to 0.36 mm; margins plane or recurved at base, serrate at apex; costa short, double, or nearly lacking; alar cells large, bullate, yellow to orange; branch leaves somewhat smaller; sexual condition autoicous; seta 0.6 to 1 cm long, capsule cylindrical, suberect, 1 to 1.5 mm long, operculum rostrate, as long as the urn (Figure 1C); peristome perfect, annulus wanting; spores 13 to 17 µm (COSEWIC 2010). See also Figure 2A–D.

Roell’s Brotherella Moss can be confused with Hypnum circinale (Coiled-leaf Claw Moss), which often occurs mixed in with some populations. H. circinale can be recognized from Roell’s Brotherella Moss by having dull, grey-green shoots and a strongly falcate, “ropy” appearance. Additional descriptions and/or illustrations of Roell’s Brotherella Moss can be found in Lawton (1971), Conard (1944), and Grout (1932).

The nested spatial terminology used in this report is defined as follows:

• subpopulation — a geographically distinct subset of the population that has little demographic or genetic exchange with other such groups. It is assumed that discrete habitat fragments surrounded by urban and residential areas (for example, municipal parks) are distinct subpopulations
• site — an area where a subpopulation (or portion of a subpopulation) of Roell’s Brotherella Moss is found
• individual — the “individual-equivalent” for bryophytes as per the IUCN guidelines presented by Bergamini et al. (2019), which states that the individual substrate on which the bryophyte is growing is counted as the mature individual. This is because it can be difficult to determine the edges of individual colonies, and in the case of tree and deadwood species, Roell’s Brotherella reflects that the population dynamics are driven by the appearance and loss of these substrates; and
• colony — a discrete patch of Roell’s Brotherella Moss. For example, a subpopulation of Roell’s Brotherella Moss comprising eight individual-equivalents (that is, individual stumps, logs, and trees) is known from the Ruby Creek site. One stump (Individual #3) had two colonies; the first colony measured 50 cm × 60 cm

Genetic description

There is no information available concerning population genetic structuring for Roell’s Brotherella Moss. While a search of the National Center for Biotechnology Information (NCBI) revealed several genetic studies on other species of Brotherella, Brotherella roellii was not listed in their Taxonomy Browser (Tucker pers. comm. 2022). Shaw et al. (2005) examined the molecular structure of B. recurvans but did not include Roell’s Brotherella Moss in their study.

Designatable units

There is no evidence at this time to indicate there are discrete and evolutionarily significant units within the population.

Special significance

Roell’s Brotherella Moss is endemic to Pacific Northwest North America. The Canadian population may represent the only known extant sites globally because the U.S.A. population is possibly extirpated.

Figure 1. (A) Roell’s Brotherella Moss habit, (B) deciduous shoots, (C) sporophytes. Photos by Dan Tucker.

Figure 2. Microscopy of Roell’s Brotherella Moss: (A) swollen bullate alar cells at the base of the leaf, (B) stem cross-section, (C) stem leaves, (D) deciduous shoots. Photos by Judith Harpel.

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 and the places where they grow. 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, Roell’s Brotherella Moss is important to Indigenous Peoples, who recognize the interrelationships of all species within the ecosystem.

Distribution

Global range

Roell’s Brotherella Moss is known only from the Lower Mainland of southwestern British Columbia in the Fraser River Valley and Howe Sound regions, as well as Washington State (Figure 3). All six known U.S. subpopulations are scattered throughout the Puget Sound area and lower Cascade Mountains and are unconfirmed and possibly extirpated. The last known collection in Washington was made in October 1913. Roell’s Brotherella Moss was also reported from Alaska by Harvill (1950) and Worley (1972), but these collections were determined by Judith Harpel to be misidentifications (COSEWIC 2010). Consequently, Roell’s Brotherella Moss is probably now a Canadian endemic.

Figure 3. Distribution of Roell’s Brotherella Moss in Canada.

Canadian range

Roell’s Brotherella Moss has been known from 58 subpopulations globally, 52 of which are in Canada, including all 30 known extant subpopulations. Roell’s Brotherella Moss was first collected by John Macoun on May 11, 1875, from “the Cascades at Yale.” A review of Macoun’s autobiography (Macoun 1922) to determine the exact coordinates indicated that he was not in the Yale area on the day the collection was made. Although the specimen is without doubt Roell’s Brotherella Moss, it appears that the label information is incorrect, and the exact site that this first collection came from is uncertain. For more details, see Fluctuations and trends. The problem of Macoun’s inaccurate locality data has been documented previously (Godfrey 1977).

Presently, Roell’s Brotherella Moss is known from 30 extant subpopulations within the Lower Mainland of the Fraser River and Howe Sound area of southwestern British Columbia (see Search effort). Twelve additional sites found in the later half of the 20th century are unconfirmed because precise coordinates of these records collected by W.B. Schofield are unknown due to vaguely written descriptions (Table 1).

Four sites are believed to be extirpated. An additional six sites (recent and historical) are extirpated (that is, the subpopulation no longer exists). In the Fraser Valley, scattered sites occur between Point Grey on the western end of Vancouver and east to Hope (Figure 3). In Howe Sound, all the sites are clustered in the Squamish area (see Table 1). Within its range, Roell’s Brotherella Moss occurs most frequently in the area between Langley and Chilliwack and all the subpopulations occur within the Coastal Western Hemlock (CWH) biogeoclimatic zone of British Columbia.

Other specimens that have been originally identified as Roell’s Brotherella Moss have been excluded. A New Brunswick Macoun collection of Brotherella roellii (deposited at the New York Botanical Garden herbarium) was determined to be B. recurvans (Recurved Brotherella), a common eastern North American species. A few collections from Vancouver Island, Calvert Island, and Haida Gwaii were determined to be Brotherella canadensis (Canadian Brotherella) by Schofield (2006). Another collection from Haida Gwaii (Bigsby Inlet 1964 W.B. Schofield 24165) is an undescribed species of Brotherella (Golinski pers. comm. 2022).

Search effort

Bryophytes in southwestern British Columbia were extensively collected by W.B. and Margaret Schofield and many of his students during the 1960s through to the late 2000s, and 19 of the known subpopulations of Roell’s Brotherella Moss were discovered by his students prior to 2007. Targeted search effort by Steve Joya between 2007 and 2010 for the initial status assessment report (COSEWIC 2010) resulted in nine new subpopulations. In the time since the previous status report, 16 new subpopulations were found by Steve Joya, Phil Henderson, and Terry McIntosh, and another 4 were found by D. Tucker in the preparation of this report (see below; Tucker unpubl. data).

It was not possible to visit all known subpopulations of Roell’s Brotherella Moss in the timeframe allotted for the preparation of this report. Therefore, in November 2021 and May 2022 a selection of 21 sites with extant or believed to be extant subpopulations (Joya pers. comm. 2021) were surveyed to represent the greatest geographic range across the known species distribution in Canada. In addition, 12 sites with potentially suitable habitat (determined via aerial imagery) were searched. Potential suitable habitat was based on qualitative macro-level habitat characteristics including humid riparian forests and the presence of substrates and microhabitats known to be occupied by the species. Potential sites were chosen by using satellite imagery and searching for mixed deciduous-conifer forests with creeks or wetland features in parks or other areas. These were ground-truthed for the appropriate microhabitats and species presence. Search effort in sites of potentially suitable habitat and with known subpopulations for the preparation of this report is summarized in Table 2.

This search resulted in the discovery of four new subpopulations: two in Chilliwack (Bridalwood Park, Promontory, Chilliwack [Subpopulation 46], and Camp Slough, Nature Trust of British Columbia [Subpopulation 45]); one in Hope (Tom Barry Road, Nature Trust of British Columbia [Subpopulation 43]), and one in Rosedale (Cheam Lake Wetlands Regional Park [Subpopulation 44]).

It is difficult to determine the amount of potential habitat for the species. Brotherella roellii grows on several substrates in humid mixed deciduous forests, including secondary growth, particularly Alder, Bitter Cherry, and Salmonberry riparian lowlands. Furthermore, it can tolerate moderately drier upland sites (especially with a creek or active drainage). Notwithstanding these broad habitat associations, and despite extensive search effort in southwestern B.C., the species nevertheless displays a very restricted distribution in Canada and western North America.

Population structure

Roell’s Brotherella Moss has small wind-dispersed spores and flagelliform shoots (a form of asexual reproduction) that disperse at shorter distances. Compared to vascular plants, moss diaspores are smaller and more easily dispersed. For bryophytes generally, low spatial genetic structure is considered the norm (Patiño and Vanderpoorten 2018). Life history of the species, environmental conditions, and geographic barriers also influence the population structure. Examination of UBC Herbarium material of Roell’s Brotherella Moss by Judith Harpel during the preparation of the 2010 COSEWIC report found that 25% of specimens had sporophytes. Sixty-nine percent of the UBC specimens were collected in the winter or spring months (December to May), when this species can be expected either to be developing or to have developed sporophytes. This implies that sporophytes are relatively common, although it is not clear whether all collectors took care to acquire sporophytes while collecting.

Extent of occurrence and area of occupancy

Extent of occurrence (EOO) was calculated as the area contained within the shortest continuous boundary (convex hull) encompassing all known, inferred, or projected sites of occurrence among extant subpopulations (as per COSEWIC 2021).

Unconfirmed records were excluded from the calculations because uncertainty in their exact coordinates made accurate estimation of EOO and IAO impossible.

Current EOO: Extent of occurrence (EOO) in Canada is 6,787 km² (Figure 3).

Current IAO: Index of area of occupancy (IAO) in Canada is 128 km², calculated using a 2 x 2 km grid drawn over known records from 2002 to 2022 (Figure 3)

Fluctuations and trends in distribution

The previous status assessment for Roell’s Brotherella Moss (COSEWIC 2010) did not explicitly define historical subpopulations but considered the original records from Macoun (1889 to 1916) as historical. Other records older than 20 years old were referred to as “old Schofield sites,” as they were collected by W.B. and Margaret Schofield in the 1960s, 1970s, and 1980s. When the EOO and IAO were recalculated from data in COSEWIC (2010) on the basis of methods from COSEWIC (2021), excluding the extirpated and historical Macoun records, the EOO in 2010 was 6,192 km², and the IAO was 88 km².

The observed increase in EOO and IAO since 2010 is due to continued search effort and the discovery of several new subpopulations, although the population is declining overall (see Fluctuations and trends).

Biology and habitat use

Life cycle and reproduction

In general, bryophyte dispersal relies on the production of spores or specialized vegetative diaspores. Unlike other members of this genus in North America, Roell’s Brotherella Moss is autoicous, having both male and female reproductive organs on the same plant. This increases the chance for successful fertilization and production of sporophytes. Sporophytes of Roell’s Brotherella Moss mature and disperse spores in the winter. Roell’s Brotherella Moss also produces deciduous flagelliform shoots, and this could provide a mechanism for asexual reproduction.

Under the guidelines of Bergamini et al. (2019), Roell’s Brotherella Moss is considered a “long-lived” species that, in the absence of detailed life history studies, is characterized by a generation time of 11 to 25 years and 50 years for three generations.

Habitat requirements

Roell’s Brotherella Moss sites are characterized as cool, humid, mixed broadleaf and conifer forests on stream terraces, swampy flood plains, and occasionally in ravines with creeks. It has been collected on the trunks of Red Alder (Alnus rubra), Bigleaf Maple (Acer macrophyllum), Western Flowering Dogwood (Cornus nuttallii), and birch (Betula spp.), and on stumps, logs, and decaying wood. Roell’s Brotherella Moss was recently observed on Bitter Cherry (Prunus emarginata) and Western Redcedar (Thuja plicata) (Tucker unpubl. data 2022). In drier sites (for example, mixed deciduous forest), colonies tend to form on late-stage decaying wood (Figure 4A), whereas, in wetter sites (for example, swampy flood plains or ravines), colonies can be found growing on living trees in addition to decaying wood at all stages (Figure 4B) (D. Tucker pers. obs. 2022). Based on previous estimates made in 2009 with Google Earth (Harpel unpubl. data 2009), the elevational range for the known subpopulations was between 4 and 100 m. However, in 2022, a new subpopulation at 130 m was discovered (Tucker unpubl. data 2022).

Figure 4. Typical habitat for Roell’s Brotherella Moss (A) in a higher elevation mixed deciduous forest, on rotting wood at Ruby Creek; and (B) in swamps and flood plains on trees at Downes Bowl Park. Photos by Dan Tucker.

Movements, migration, and dispersal

Typically, successful colonization of bryophytes is dependent on the availability of viable propagules, such as wind-dispersed spores from nearby subpopulations, as well as appropriate establishment substrate and microclimatic conditions (for example, Palmer 1986; Söderstöm 1988; Schmitt and Slack 1990; Király et al. 2013).

Löbel and Rydin (2010) identified trade-offs between dispersal ability, spore size, desiccation tolerance, and germination and protonemal growth rates among epiphytic bryophytes. Small spores (<20 µm), such as those of Roell’s Brotherella Moss, can disperse farther, germinate, and develop protonemata faster than larger spores, but at the cost of being more sensitive to desiccation. This desiccation intolerance may help explain why Roell’s Brotherella Moss prefers humid sites and is not frequent on the landscape. Small spores can disperse over large distances, with spatial patterns identified at the scale of tens of kilometres, or regions, such as the EOO of Roell’s Brotherella Moss (Barbé et al. 2016). Dispersal via deciduous flagelliform shoots is a possible way to clone a new colony, but these shoots are large and not easily dispersed over long distances. This type of asexual diaspore is typically more successful than spores (Löbel and Rydin 2010).

Interspecific interactions

Interspecific interactions such as host/parasite, herbivory, and competition are unknown for Roell’s Brotherella Moss. However, Roell’s Brotherella Moss has been observed occurring with other bryophyte species such as Bazzania denudate (Naked Whipwort), Hypnum circinale (Coiled-leaf Claw Moss), Isothecium stoloniferum, and Rhytidiadelphus loreus (Lanky Moss). Invasive vascular plants such as Himalayan Blackberry (Rubus armeniacus) and English Ivy (Hedera helix) growing out of stumps and rotting logs may also compete with Roell’s Brotherella Moss (see Threats).

Physiological, behavioural, and other adaptations

The physiology and adaptability of Roell’s Brotherella Moss has not been studied; however, bryophytes generally obtain water and nutrients by intercepting and absorbing solutes in rainwater, cloud and mist droplets, and airborne dust through their shoots (Glime 2021). Given that Roell’s Brotherella Moss grows on various woody debris (which hold moisture) and on living tree species in humid mixed deciduous woodland, flood plains, and creeks, it is likely that local humidity is critically important for defining the fundamental niche. Survival in sites of low humidity is unlikely, even if the appropriate substrates exist.

Limiting factors

Factors limiting the population of Roell’s Brotherella Moss have not been studied but may include strict niche requirements pertaining to environmental factors such as high humidity and low light.

Population sizes and trends

Data sources, methodologies, and uncertainties

Coordinates and habitat data on extant, unconfirmed, and extirpated subpopulations were compiled from the UBC Bryophyte Herbarium, B.C. Conservation Data Centre, North American Consortium of Bryophyte Herbaria (CNABH 2022), and the personal notebooks, reports, and collections of S. Joya, T. McIntosh, and P. Henderson. For the targeted field verification surveys in November 2021 and May 2022, GPS coordinates, habitat description, number of individual-equivalents, colony size (Appendix 1), and any potential threats were noted for each observed subpopulation. Photographs were taken of every individual-equivalent found at each site to aid with future relocation and habitat assessment. Search effort at each site was also recorded (Table 2). Considerable uncertainty in the exact coordinates exists among some of the unconfirmed subpopulations originally collected by W.B. and Margaret Schofield. This uncertainty combined with vague habitat descriptions made these subpopulations impossible to locate. Many individual collections were examined (Appendix 2).

Abundance

According to Schofield (2006), “… although the species (B. roellii) is widely distributed within a restricted area of southwestern British Columbia, it is never common in spite of the fact that most populations occur in second-growth forest.” The rarity of the species is reiterated by O.D. Allen on a handwritten note found in a February 1903 collection of B. roellii from the Cascades in Washington. He comments, “I know but one locality. It grows on sides of large much decayed logs in woods, probably rare.”

Based on the “individual-equivalent” for bryophytes as per the IUCN guidelines (Bergamini et al. 2019), a mature individual of Roell’s Brotherella Moss can be considered as the tree, log, or stump that supports one or more colonies of the moss growing on it. The number of individuals and size of the colonies found at a site has often not been noted by the collector. However, in some cases there are qualitative comments on abundance on herbarium labels (for example, “locally abundant,” S. Joya UBC B203303). At recently surveyed sites, the number of individuals (trees, logs, stumps) observed has been recorded more frequently and included on herbarium labels and in field notebooks, and this can help to estimate abundance. To estimate abundance conservatively, sites without a history of abundance data can only be considered to hold a single individual. Based on the most recent surveys, there are approximately 94 individuals (known, 106 including 12 unconfirmed subpopulations) of Roell’s Brotherella Moss in Canada (Table 1). Additional surveys may discover more individuals. However, given the intensity of surveys to date, it is unlikely that the number of individuals will exceed 2,500 mature individuals, and it will certainly remain fewer than 10,000 mature individuals. Appendix 2 summarizes the number of individuals and the colony measurements recorded during the 2021 and 2022 field verification surveys for this report.

Fluctuations and trends

The inferred decline of the Canadian population of Roell’s Brotherella Moss has been attributed to habitat loss due to urban expansion and human settlement, recreational use, road construction, agriculture, resource extraction, and industrial development (COSEWIC 2010). It was assumed that the current sites represent relicts of a broader distribution (COSEWIC 2010), an assumption made with little information about the historical abundance of individuals and subpopulations. It is unlikely that this species experiences extreme fluctuations.

Changes in population size can be evaluated via changes in the number of subpopulations and in the size of individual subpopulations. Examining first subpopulations, 32 subpopulations were known in 2010 (COSEWIC 2010). Since the last report, an additional 20 subpopulations were found, for a total of 52 known subpopulations.

Several historical subpopulations were already considered extirpated in the COSEWIC 2010 report. This included three of the earliest collections by Macoun: Agassiz (Subpopulation 5), Hastings (Subpopulation 26), Yale (Subpopulation 40). According to Macoun (1922), on May 14, 1875, he took a steamer from Victoria to New Westminster. The next day, they left the area and reached the Harrison River by dark. This suggests that his Yale collection dated May 11, 1875, may have been collected somewhere in what is now the Vancouver or Delta area. Macoun’s 1889 Hastings site is now part of Gastown in downtown Vancouver, and the 1889 Agassiz site appears to have been replaced by agricultural and urban development.

More recently documented in the 2010 report, in 2009, a subpopulation of Roell’s Brotherella Moss was extirpated from the Pacific Spirit Regional Park, Southlands School site (Subpopulation 24) when the two individual-equivalents were lost: a rotten log was destroyed by a recently fallen tree (COSEWIC 2010), and an alder tree was cut down during a trail-widening project. A second subpopulation was listed as extirpated in 2010, when, in the Howe Sound area, the Squamish highway site (Subpopulation 41) located by W.B. Schofield in 1970 was destroyed by construction to widen the road in preparation for the 2010 Winter Olympics (COSEWIC 2010).

In the 12 years between the 2010 status report (COSEWIC 2010) and the field work for this report, five additional subpopulations have been extirpated or no colonies were found in most recent visits. In 2012, S. Joya found a colony of Roell’s Brotherella Moss growing on a decaying log spanning the creek in Kyle Creek Ravine, Port Moody (Subpopulation 30). In November 2021, D. Tucker and T. McIntosh searched the ravine, but the original colony could not be located, and recent storm flow in the creek had left a damaged, decaying log on the creek bed, indicating that the colony had likely been destroyed by high water flow.

There were no colonies found at four additional sites, and it is possible that they were extirpated. Because of the extensive search effort made at the sites, the following subpopulations should be considered extirpated at this time: Kawkawa Lake (Hope) (Subpopulation 31), Kanaka Creek (Maple Ridge) (Subpopulation 14), Burnaby Mountain, Mel’s Trail (Burnaby) (Subpopulation 32), and Pacific Spirit Regional Park, near the Shaughnessy Golf Course (Vancouver) (Subpopulation 23). An additional reason to believe these sites are extirpated is that the report author successfully found new colonies in several other subpopulations where the original individual-equivalent had disappeared, for example, in Subpopulation 1 (Tucker pers. comm 2022). In 2010, four colonies (together comprising a single individual-equivalent) of Roell’s Brotherella Moss were found on a log along the Sumas Mountain Glen Ryder Trail (Subpopulation 1). Previously a healthy individual, it had degraded over time with intensified recreational trail use, and the subpopulation was feared to have been extirpated from this site (P. Henderson, pers. comm. 2022). Investigation of the site in May 2022 and comparison with photos from 2010 confirmed the original log was no longer present. However, further searching in the near vicinity revealed a new individual (one colony) on a different log in the forest within 30 m of the original log.

Finally, 12 subpopulations are undocumented since their discovery by Schofield. Unfortunately, the status of these subpopulations is unknown, and they cannot be used to calculate fluctuations.

In summary, of the 40 populations for which there is information, 7 subpopulations have been extirpated recently: 2 were lost shortly before the 2010 COSEWIC report (excluding the historical Macoun subpopulations) and 1 population is extirpated and 4 are assumed to be extirpated between 2010 and 2022.

It is not possible to estimate population trends for Roell’s Brotherella Moss at the individual level, because no appropriate subpopulation-level data exist, that is, there are only a few measures of the number of individual-equivalents per subpopulation and, of these, there are only data from the most recent inventory. However, in several cases, there is documentation of loss or decline of the original colony followed by recolonization of new substrates in proximity (for example, subpopulations 1, 16).

Continuing decline^{Footnote 1} in number of mature individuals

The 12 unconfirmed subpopulations for which we have only imprecise locations are excluded from this calculation. A continuing decline of uncertain magnitude in the number of mature individuals is inferred, based on fluctuations in the number of subpopulations. Several subpopulations have remained extant for over 50 years (for example, subpopulations 8, 9, 16), suggesting that subpopulations are generally stable over time in the absence of an anthropogenic, climate change–driven, or stochastic disturbance. Given the general stability of subpopulations, the new (20) subpopulations found since 2010 were probably present previously and had simply not been identified. Consequently, there are 40 (of 52) subpopulations for which there is information over time. Of these 40, 3 were lost more than three generations ago (the 3 Macoun sites), and 7 subpopulations were lost in the last three generations: 2 before 2010, and 5 after. A conservative estimate of loss over three generations is therefore 7/40 = 17.5%, or a more realistic loss is 7/37 = 18.9%. Since the last report in 2010, when there were 35 extant populations (including the 20 found since but presumed to have been present), the most accurate description of loss would be 5/35 = 14.28%.

It is not possible to count the number of individual-equivalents this represents as the number of individual-equivalents in the lost sites is unknown.

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

The generation time of Roell’s Brotherella Moss is 11 to 25 years. Within three generations, or 75 years, seven subpopulations have been lost, with the loss of two to three of the historic sites found by Macoun possibly predating this time.

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

While many subpopulations are threatened because of continued climate change–associated disturbances in addition to human pressure, the future decline rate in the number of mature individuals is uncertain.

Long-term trends

Long-term trends in the number of mature individuals are uncertain; however, it is assumed that agricultural development and residential development since the early 1900s in the Fraser Valley have destroyed many individuals of Roell’s Brotherella Moss.

Population fluctuations, including extreme fluctuations

The number of mature individuals has not been estimated previously and, therefore, fluctuations cannot be determined, but there is no reason to believe this species experiences extreme fluctuations.

Severe fragmentation

Dispersal ability and population structure have not been studied for Roell’s Brotherella Moss. Roell’s Brotherella Moss requires only a single tree, stump, or rotting log for substrate, so the habitat size per se is not expected to impact long-term population viability if the substrate and environmental conditions persist. However, small fragments of habitat such as urban parks are subject to high recreational pressure, which threatens the long-term viability of those subpopulations.

Rescue effect

The possibility of rescue effect from the U.S. population of Roell’s Brotherella Moss is very low. Although there are known sites in Canada near the United States border, the known population in Washington is listed as possibly extirpated. Furthermore, extensive agricultural development on both sides of the border limit potential habitat for this species.

Threats

Historical, long-term, and continuing habitat trends

Past agricultural and industrial development in the Lower Mainland has likely eliminated many subpopulations of Roell’s Brotherella Moss; however, this threat is likely in the past.

Current and projected future threats

The threats to Roell’s Brotherella Moss were assessed following the IUCN-CMP (International Union for the Conservation of Nature – Conservation Measures Partnership) unified threat classification system (see Salafsky et al. 2008 for definitions and Master et al. 2012 for guidelines).

The overall threat Calculated Impacts assigned to Roell’s Brotherella Moss is “High – Medium” (Appendix 3).

The most serious and plausible threats to Roell’s Brotherella Moss are cumulative and include especially climate change–associated flooding and drought, invasive species, and urbanization and human intrusion. They are discussed below in decreasing order of impact (see Appendix 3 for details).

Climate change (IUCN 11; overall threat impact: medium – low)

The species most vulnerable to the effects of climate change in British Columbia are those with small populations, slow rates of dispersal, restricted elevation, specific climatic requirements, and whose habitat is restricted to fragments (Gayton 2008). Most of these characteristics fit Roell’s Brotherella Moss; however, considering that climatic envelopes (biologically relevant climate variables correlated with current biogeoclimatic zones; see Wang et al. 2012) are expected to shift north and upslope (Gayton 2008), potential habitat for Roell’s Brotherella Moss (which is currently restricted to lower elevations) may expand, assuming dispersal is possible and there are still ample substrates and microhabitats at higher elevations.

Storms and flooding (threat category 11.4; threat impact: medium – low)

Storms and flooding threaten Roell’s Brotherella Moss by two mechanisms: slow inundation and siltation, and high energy storm flow. Both of these mechanisms could occur (and co-occur) as a result of large precipitation events and might lead to mortality of Roell’s Brotherella Moss individuals. Nine of thirty extant subpopulations (or 32/106 individual-equivalents; 30% of the Canadian population) of Roell’s Brotherella Moss are found within flood plains and could be eliminated by these storm events (Ministry of Environment 2008; FVRD 2019). Smaller localized storm surges in creeks and ravines could eliminate individuals growing close to those boundaries, especially those on woody debris which is not well rooted in the ground (for example, log destroyed in Kyle Creek Ravine, Port Moody, in the November 2021 storm surge). It is unclear how long individuals growing on living trees could survive inundation, but it seems unlikely that brief inundation would destroy these subpopulations. Due to human-induced climate change, peak streamflow in extreme precipitation events has increased by 13 to 16% in the Lower Mainland of B.C. and the probability of large-scale flooding (as experienced in November 2021) has increased by 120 to 330% when compared to a 1950 to 1969 baseline (Gillett et al. 2022). The threat from localized storm surges and widespread flooding will likely continue and increase in impact in the future.

Droughts (threat category 11.2; threat impact: unknown)

Roell’s Brotherella Moss is restricted to humid habitats (ravines, wetlands) and humid substrates in drier habitats (wet woody debris in humid mixed deciduous forests); therefore, drought could negatively affect the species. The median snowfall in the South Coast region of British Columbia is projected to decrease by 24 to 52% (PCIC 2013) by the 2050s based on a 1960 to 1991 baseline. This will impact stream volumes, flow patterning, and discharge of groundwater in downslope watersheds. This decrease in moisture coupled with increasing summer temperatures (PCIC 2013), could lead to prolonged drought conditions. Furthermore, regional warming and drought stress have been attributed to widespread increases in tree mortality rates (doubling every 17 years) in the Pacific Northwest in the period of 1970 to 2006 (Van Mantgem et al. 2009). Subpopulations of Roell’s Brotherella Moss growing on living trees may be damaged or eliminated as their host mortality rate increases in response to drought.

Invasive and other problematic species, genes and diseases (IUCN 8; overall threat impact: medium – low)

Invasive species (threat category 8.1; threat impact: medium – low)

As many of the subpopulations of Roell’s Brotherella Moss are found at sites in urban areas, invasive species are also frequently encountered. Interactions between invasive species and Roell’s Brotherella Moss do occur. For example, at Mount Shannon Park in Chilliwack (Subpopulation 29), the subpopulation is growing on a Western Redcedar stump that as of May 2022 is starting to be colonized by invasive English Ivy. As well, the rotten log adjacent to the Glen Ryder Trail on Sumas Mountain (Subpopulation 1) has invasive Himalayan Blackberry brambles growing over it. Invasive plants may outcompete Roell’s Brotherella Moss for light and nutrients and alter the substrate characteristics and microclimate around the affected individual. This threat can be expected to continue at sites in urban areas but can be mitigated by invasive plant removal.

Residential and commercial development (IUCN 1; overall threat impact: low)

Housing and urban areas (threat category 1.1; threat impact: low)

Most of the known subpopulations of Roell’s Brotherella Moss are found in urban areas of the Fraser Valley and Squamish. Housing and urban area development could result in the destruction of individuals, or habitat loss, including via increased edge effect from land clearing. According to a census completed by Statistics Canada, human population growth in municipalities within the range of Roell’s Brotherella Moss has increased 8 to 22% from 2016 to 2021 (Statistics Canada 2021). In particular, the municipality of Squamish has experienced the greatest population growth in this period and is the fourth fastest-growing municipality in the province (Statistics Canada 2021). However, many of the known subpopulations in urban areas are found within regional and municipal parks which may provide some protection from development (Table 1). Fifty-three percent of extant subpopulations (16/30) but only 29% percent of individual-equivalents (31/106 individuals) of the Canadian population are on Crown, municipal, or First Nations land and could be threatened with development in the future. However, at the only subpopulation site currently experiencing development, the Skwah First Nation #4 in Chilliwack (Subpopulation 50), there has been transplanting of the logs and stumps with Roell’s Brotherella Moss away from the development area, overseen by an expert bryologist (McIntosh pers. comm. 2022).

Tourism and recreation areas (threat category 1.3; threat impact: low)

Fourteen of thirty extant subpopulations or 47% (42/106 individual-equivalents) of Roell’s Brotherella Moss are in parks (Table 1). Historically, trail maintenance, construction, or expansion of human use areas and facilities (for example, restrooms, parking lots, entrance roads) have damaged or eliminated subpopulations within parks (for example, subpopulations in Pacific Spirit Park, Southlands, Bridal Veil Falls Provincial Park [COSEWIC 2010]). In 2022, at Abbotsford’s Ravine Park, an individual was found on a recently felled alder tree along a main trail.

Transportation and service corridors (IUCN 4; overall threat impact: low)

Utility and service lines (threat category 4.2; threat impact: low)

The path of the Trans Mountain Pipeline is close to the subpopulation (n = 1 individual) found 150 m west of the Bridal Veil Falls Park boundary (Subpopulation 46) (Trans Mountain Pipeline ULC 2019). Forest clearing for the pipeline construction may create edge effects (for example, increased windblown disturbance and altered microclimate) which can extend greater than 45 m into the forest and impact bryophyte communities (Baldwin and Bradfield 2005). T. McIntosh plans to oversee the relocation of the stump at the pipeline site if it is determined to be in the construction area.

Biological resource use (IUCN 5; overall threat impact: low)

Logging and wood harvesting (threat category 5.3; threat impact: low)

Twenty-five percent of the Canadian population (26/106 individuals, eight extant and unconfirmed subpopulations) are on Crown or First Nations land, and it is possible that wood harvesting for fuel or logging in the vicinity could impact subpopulations at those sites. However, because Roell’s Brotherella Moss can grow both on trees and decaying wood, it is adapted to a substrate that decays and degrades naturally over time. As well, Roell’s Brotherella Moss is mostly found on broadleaf tree species of relatively low timber value, and the risk of its host trees being deliberately logged is small. Additionally, the trees on which Roell’s Brotherella Moss is most commonly found growing (for example, Red Alder, Bitter Cherry, Paper Birch) are usually dominant in secondary succession forests, which develop after disturbances, such as logging. Currently, there are no active logging operations or indications of wood harvesting at sites of Roell’s Brotherella Moss.

Human intrusions and disturbance (IUCN 6; overall threat impact: low)

Recreational activities (threat category 6.1; threat impact: low)

Many of the 14 subpopulations in parks are found along major trails which experience recreational traffic. Foot traffic has eliminated individuals of Roell’s Brotherella Moss in the past (for example, the original Sumas Mountain Glen Ryder Trail individual — Subpopulation 1). The possibility of damage from recreational activity is higher for individuals found on rotting logs as opposed to living trees and stumps. Eleven individuals (10% of the Canadian population) are found on rotting logs near trails in Gardener Park (Subpopulation 48), Southern Park (Subpopulation 49), Century Park (Subpopulation 3), Ravine Park (Subpopulation 4), Downes Bowl Park (Subpopulation 2), Squamish Rotary Park (Subpopulation 18), and West Creek Wetlands. The individuals on logs found at the West Creek Wetlands (Wood Duck Lake) (Subpopulation 28) site in Langley are likely at reduced risk of trampling in comparison with the other subpopulations because this site has restricted access and reduced foot traffic. At the Great Blue Heron Nature Reserve (Subpopulation 47), a large colony is found on a log used as an interpretive display directly adjacent to a popular trail. While probably safe from trampling due to the log’s visibility and interpretive use, the individual could be unknowingly damaged if the display is manipulated or moved. Mountain biking is another recreational threat to subpopulations of Roell’s Brotherella Moss. In particular, the individual on Mount Shannon in Chilliwack (Subpopulation 29) appears to be located at the intersection of several popular mountain biking trails. Recreational pressure on parks will likely increase with human population growth, and these activities will continue to be a threat to the remaining subpopulations of Roell’s Brotherella Moss.

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

Fire and fire suppression (threat category 7.1; threat impact: low)

As Roell’s Brotherella Moss is typically found in ravines, wetlands, and mixed deciduous forest, the risk of wildfire to the known subpopulations is low. However, accidental human-caused fires may occur. Accidental fire may be caused by cigarettes in municipal or regional parks and on Crown and First Nations land. However, the risk is likely lower for Crown and First Nations land due to lower visitor traffic. Though, for the same reason, on Crown and First Nations land, improperly contained campfires or dumping of flammable materials may threaten subpopulations at those sites. For example, the Ruby Creek (Subpopulation 16) site is located close to the highway, and an area within 30 m of the site appears to be used as a temporary campsite and dumping spot. As well, improperly stored flammable chemicals at a property adjacent to the Tom Barry Road, Nature Trust of B.C. site (Subpopulation 43) in Hope (Sara Connal, Site Caretaker, pers. comm. 2022) could pose a fire hazard. The threat of accidental human-caused fires is expected to continue.

Geological events (IUCN 10; overall threat impact: low)

Avalanches/landslides (threat category 10.3; threat impact: low)

In the Fraser Valley and in Howe Sound, large rockslides, avalanches, and channelized debris flows have occurred for millennia (Evans and Savigny 1994). In the last 10,000 years, large landslides have occurred in Cheam (5010 ± 70 BP), Katz (3260 ± 70 BP), and Hope (9680 ± 320 BP) (Evans and Savigny 1994; Orwin et al. 2004), which can be seen in the geology of those areas. Canada’s second-largest rockslide disaster (1915, Britannia Mine) occurred in Howe Sound, and channelized debris flows (triggered by heavy precipitation) still occur frequently throughout the region (Evans and Savigny 1994). Recently, in November 2021, a high precipitation “atmospheric river” event triggered several channelized debris flows in the Fraser Valley (Global News 2021). Multiple landslides occurred in Ruby Creek and between Popkum and Hope. While these localized events did not impact any known subpopulations of Roell’s Brotherella Moss, the subpopulations (three subpopulations; 14/106 individuals; 13% of the Canadian population) located at Ruby Creek (Subpopulation 16), Seabird Island (Subpopulation 17), and Bridal Veil Falls Provincial Park (Subpopulation 9) may be susceptible to landslides in the future. Climate change is predicted to alter antecedent and short-term precipitation and, as a result, the frequency of landslides in southwestern B.C. is expected to increase (Jakob and Lambert 2009), which suggests that these events will continue and expand in scope over time.

Number of locations

The number of locations is much greater than 10, as the most serious plausible threats of residential development, human intrusions (for example, recreational activity), and some of the effects of climate change are widespread throughout the species’ range but have impacts which are localized (for example, landslides, storm surges).

Protection, status, and recovery activities

Legal protection and status

Roell’s Brotherella Moss is currently designated Endangered and is protected under Schedule 1 of the Species at Risk Act. In British Columbia, Roell’s Brotherella Moss is not protected under the Wildlife Act or any other legislation.

Non-legal status and ranks

Roell’s Brotherella Moss was ranked as G3 (Vulnerable) in 2004. A recent re-evaluation of Roell’s Brotherella Moss by NatureServe (2025) unfortunately did not fully explore the supposed taxonomic confusion, as has been done for this report. Consequently, the recent revisions to the status are not included here.

Land tenure and ownership

Fourteen (47%) of the 30 extant subpopulations of Roell’s Brotherella Moss are protected in provincial, regional, or municipal parks. An additional two sites are protected on private lands of the Nature Trust of British Columbia, and two more sites are on Department of National Defence land. One additional subpopulation is protected on private property of an ecological reserve owned by the North Vancouver School District and operated by the Cheakamus Outdoor Education Centre, near Squamish. Five subpopulations are on First Nations land, and the remaining extant subpopulations are found on Crown land or private subdivisions. See Table 1 for site-specific land tenures.

Recovery activities

• 2013 Recovery Plan for Roell’s Brotherella in British Columbia (Ministry of Environment 2013)
• 2021 Federal Recovery Strategy for Roell’s Brotherella (Environment and Climate Change Canada 2021)

Information sources

References cited

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Authorities contacted

• Connal, S. Site Caretaker. Tom Berry Road, Nature Trust of British Columbia. Hope, British Columbia
• Foster, R. Vice-president. Mossom Creek Hatchery. Burnaby, British Columbia
• Golinski, K. Collections Curator. UBC Herbarium. Vancouver, British Columbia Canada
• Henderson, P. Botanist. Langley, British Columbia
• Jarvis, J. Resource Biologist. Metro Vancouver. Vancouver, British Columbia
• Jia, Y. Botanist. Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences. Beijing, China
• Joya, S. Bryologist. Vancouver, British Columbia
• Knopp, D. Site Caretaker. Camp Slough, Nature Trust of British Columbia. Chilliwack, British Columbia
• McIntosh, T. Bryologist. Vancouver, British Columbia
• McNaughton, C. Conservation Land Manager. Nature Trust of British Columbia. Vancouver, British Columbia
• Mindell, R. Bryologist. Courtenay, British Columbia
• Penny, J. Program Botanist. B.C. Conservation Data Centre. Victoria, British Columbia
• Sadler, K.D. Head. Species at Risk Recovery, Environment and Climate Change Canada. Nanaimo, British Columbia
• Simon, A. Botanist. Galiano Island, British Columbia
• Wu, J. Science Officer. Committee on the Status of Endangered Wildlife in Canada. Gatineau, Quebec
• Young, S. Managing Director. Skawahlook First Nation. Agassiz, British Columbia

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. The report writer would like to thank Terry McIntosh, Steve Joya, Phil Henderson, Randal Mindell, and John Reynolds for data, photos, and field assistance, Karen Golinski for reviewing the report manuscript and providing data from the UBC Herbarium, and Kella Sadler and Jennifer Penny for facilitating access to the B.C. Conservation Data Centre and draft Federal Recovery Strategy.

Biographical summary of report writer(s)

Dan Tucker is a bryologist and M.Sc. student at the University of Victoria in British Columbia. His research focuses on the biodiversity and ecology of bryophytes. Dan received his B.Sc. from the University of Alberta in 2020.

Appendix 1. Habitat and abundance summary of Roell’s Brotherella Moss individuals found in field verification surveys in November 2021 and May 2022

This table has been modified to remove precise location information. Please contact the COSEWIC Secretariat if you require this information.

Appendix 2. Collections examined

Collections were queried and examined from the UBC Herbarium. Additional records were queried from the Consortium of North American Bryophyte Herbaria (CNABH 2022), and from the personal herbarium of S. Joya.

Collections queried and examined from the UBC Herbarium. Data provided by Karen Golinksi, Curator, UBC Herbarium.

Appendix 3. Threats calculator assessment for Roell’s Brotherella Moss (Brotherella roellii)

Species Scientific name: Roell’s Brotherella Moss (Brotherella roellii)

Date: 8/8/2023

Assessor(s):

Moderator: Dwayne Leptizki (COSEWIC member)
SR writer: Daniel Tucker
M&L SSC: René Belland (Co-chair), Richard Caners, Karen Golinski, Marc Favreau, Tegan Padgett, Jurisdictions: Carrina Maslovat (BC)

References:: Draft calculator provided by report writer based on draft COSEWIC report

Assigned overall threat impact: BC = High - Medium

Impact adjustment reasons: Not applicable

Overall threat comments: Not applicable