Slender Yoke-moss (Zygodon gracilis): COSEWIC assessment and status report 2019

Official title: COSEWIC Assessment and Status Report on the Slender Yoke-moss (Zygodon gracilis) in Canada 2019

Committee on the status of Endangered Wildlife in Canada (COSEWIC)
Endangered 2019

COSEWIC assessment summary

Assessment summary – November 2019

Common name: Slender Yoke-moss

Scientific name: Zygodon gracilis

Status: Endangered

Reason for designation: In North America, this moss is confined to a single location on Haida Gwaii, British Columbia. The extremely small population occurs on a one square-metre patch of limestone cliff face near the ocean. Imminent threats to the species are the proliferation of young, dense woody vegetation adjacent to the cliff, exerting both direct (increased shade and moisture) and indirect (overgrowth by cyanobacteria) effects on the population. Other important threats include altered precipitation patterns, droughts and temperature extremes associated with climate change, quarrying of the high-quality Sadler limestone on which the species grows, and stochastic events such as inundation by tsunamis.

Occurrence: British Columbia

Status history: Designated Endangered in November 2019.

COSEWIC executive summary

Slender Yoke-moss
Zygodon gracilis

Wildlife species description and significance

Slender Yoke-moss (Zygodon gracilis) is a small to medium-sized, yellowish- to brownish-green moss that grows on dry vertical rock surfaces. The lanceolate to oblong-lanceolate leaves are spreading and recurved (bent backward) when wet and contorted and incurved when dry. The leaf margins are sharply toothed near the leaf apex and untoothed near the base. The prominent costa or “midrib” of the leaf extends to the leaf apex or just beyond. Spore-producing capsules have not been observed in Canada and have seldom been seen elsewhere.

The species is significant for its global rarity. The Canadian population is thought to have persisted in a coastal refugium during the last glaciation.

Distribution

Slender Yoke-moss is extremely rare. Its pattern of distribution has been characterized as “Western European-Western North American”. In North America the species is known from a single location on Moresby Island on the archipelago of Haida Gwaii (formerly known as the Queen Charlotte Islands) in British Columbia, Canada. Elsewhere it has been collected from one location in northern England, one in Poland, a few in the Alps (Austria, France, Germany, Italy, and Switzerland) and a few in the western Carpathian Mountains (Poland, Romania, and Slovakia).

Habitat

Slender Yoke-moss is a lithophyte (i.e., it grows only on rock). It typically colonizes dry limestone cliff faces in humid areas, but in England it occupies rock walls constructed of Carboniferous limestone.

Biology

Slender Yoke-moss has been observed in the same location for multiple decades in several countries. Male and female reproductive structures occur on separate plants, but sporophytes (spore-producing structures) have rarely been seen. Although specialized asexual reproductive structures have been induced in culture, they have not been found on plants in the wild. Therefore, it is unlikely that the Canadian population could increase by dispersal of spores. Rather, it persists through long-term clonal growth.

As a habitat-specialist occurring on dry vertical surfaces of very pure limestone in areas with high humidity, it is unlikely that Slender Yoke-moss could survive or successfully compete against other species if habitat conditions such as light, moisture, and air flow change.

Population size and trends

The population of Slender Yoke-moss in Canada consists of several small colonies (maximum 2 cm2) scattered in an area of <1 m2 on a vertical cliff face. The species was first discovered in 1961 and last observed 2018. The number of colonies was not documented in 1961, 1966, 1994, or when it was rediscovered in 2018. Based on the concept of ‘an individual-equivalent’, which has been adopted by the IUCN, the size of the population of Slender Yoke-moss is Canada is one, based on the single cliff face occupied by the species.

Threats and limiting factors

The most significant threats to Slender Yoke-moss are quarrying; impacts to the moss’s habitat caused by young native trees; stochastic events like tsunamis; and the effects of climate change such as droughts and increased temperatures. The species could also be threatened by over-collecting for scientific study.

The main factors limiting Slender Yoke-moss are its apparent lack of reproduction; small populations throughout much of its range; a disjunct pattern of global distribution; and highly restricted habitat.

Protection, status, and ranks

The global conservation status of Slender Yoke-moss is “Imperiled”. It has been identified as a candidate for the IUCN Red List of European Bryophytes based on the following conservation ranks (by country): Austria (“Risk Assumed”), Switzerland (“Vulnerable”), Germany (“Extremely Rare”), Great Britain, Italy, and Poland (“Endangered”), and Slovakia (“Critically Endangered”). The species is confirmed from France and present in Romania but its conservation status in those countries has not been assessed.

In Canada, Slender Yoke-moss has been designated as “Critically Imperiled” at the national level. It is also “Critically Imperiled” in British Columbia and is included in the province’s Red List. It is not currently protected under the federal Species at Risk Act or theBritish Columbia Wildlife Act, or by any other legislation in Canada.

Technical summary

Scientific name: Zygodon gracilis

English name: Slender Yoke-moss

French name: Houppe gracile

Range of occurrence in Canada: British Columbia

^* See Definitions and Abbreviations on COSEWIC web site and IUCN (Feb 2014) for more information on this term

Quantitative analysis

Probability of extinction in the wild is at least [20% within 20 years or 5 generations, or 10% within 100 years]: Not calculated

Threats (actual or imminent, to populations or habitats, from highest impact to least)

Was a threats calculator completed for this species? Yes.

Key threats to Slender Yoke-moss identified in the draft IUCN Threats Assessment (Appendix 1) include quarrying, problematic native species (trees), tsunamis, droughts, and temperature extremes. For details see Threats and Limiting Factors in this report, and Appendix 1.

3 Energy production and mining
3.2 Mining and quarrying

11 Climate change and severe weather
11.2 Droughts
11.3 Temperature extremes

10 Geological events
10.2 Earthquakes and tsunamis

8 Invasive / non-native and other problematic species and genes
8.2 Problematic native species / diseases

Other threats considered in the assessment were:

6 Human intrusions and disturbance
6.3 Work and other activities: site verification and monitoring

8 Invasive / non-native and other problematic species and genes
8.1 Invasive non-native/alien species/diseases

11 Climate change and severe weather
11.1 Habitat shifting and alteration

What additional limiting factors are relevant?

Key biological and environmental factors limiting Slender Yoke-moss include the uncommon and patchily distributed habitat of dry, highly pure limestone cliffs with a north to northwest-facing aspect in humid sites; local and global rarity of the species; the long distance between the Canadian population andpopulations in Europe; and an absence of reproduction or other known means of dispersal.

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

Data sensitive species

Is this a data sensitive species? Yes. Its extreme rarity likely makes it attractive to collectors.

Status history

COSEWIC Status History: Designated Endangered in November 2019

Status and reasons for designation

Status: Endangered

Alpha-numeric codes: B1ab(iii)+2ab(iii); C2a(i); D1

Reasons for designation: In North America, this moss is confined to a single location on Haida Gwaii, British Columbia. The extremely small population occurs on a one square-metre patch of limestone cliff face near the ocean. Imminent threats to the species are the proliferation of young, dense woody vegetation adjacent to the cliff, exerting both direct (increased shade and moisture) and indirect (overgrowth by cyanobacteria) effects on the population. Other important threats include altered precipitation patterns, droughts and temperature extremes associated with climate change, quarrying of the high-quality Sadler limestone on which the species grows, and stochastic events such as inundation by tsunamis.

Applicability of criteria

Criterion A (Decline in Total Number of Mature Individuals): Not applicable. There are no data to calculate percent decline.

Criterion B (Small Distribution Range and Decline or Fluctuation): Meets Endangered, B1ab(iii)+2ab(iii), because EOO and IAO are below the threshold and there is one location; and there is an inferred decline in quality of habitat.

Criterion C (Small and Declining Number of Mature Individuals): Meets Endangered, C2a(i), because there is an inferred continuing decline, the number of mature individuals is well below the threshold of 2500 individuals, and no subpopulation is expected to exceed 250 individuals.

Criterion D (Very Small or Restricted Population): Meets Endangered, D1, based on the number of mature individuals being 1, which is far fewer than 250. Haida Gwaii in general, and particularly limestone habitats throughout the archipelago, have been well-surveyed by bryologists. The very small Canadian population is consistent with global populations of the species as suggested by its conservation status in the countries where it occurs and its “G2” Global Conservation Status.

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

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

Common Name (English): Slender Yoke-moss

Common Name (French): Houppe gracile

Scientific name: Zygodon gracilis Wilson

Synonyms: Zygodon nowellii Schimp.; Zygodon viridissimus var. saxicola Molendo (Karttunen 1984; Tropicos 2019).

Family: Orthotrichaceae Arn.

There are approximately 90 species of Zygodon throughout the world, including five from North America. Three have been found in British Columbia: Z. gracilis, Z. reinwardtii and Z. viridissimus var. rupestris (Vitt 2014). Slender Yoke-moss was first collected in North America by W.B. Schofield in 1961.

Morphological description

Slender Yoke-moss is a small to medium-sized, yellowish- to dark-green moss that grows on cliff faces and rock walls. The shoots are up to 5 cm tall and have lanceolate to oblong-lanceolate leaves. The leaves are spreading and recurved (bent backward) when wet and contorted and incurved when dry. The margins of the leaves are sharply toothed near the leaf apex and entire (untoothed) toward the base. The prominent costa (or midrib of the leaf) almost reaches or extends just beyond the leaf apex. Sporophytes (spore-producing structures) are unknown in Canada and have rarely been observed elsewhere (Altherton et al. 2010; Vitt 2014; Stebel and Zarnowiec 2017).

Population spatial structure and variability

Slender Yoke-moss is known from one occurrence in Canada and the spatial structure and variability of the population has not been studied.

Designatable units

The Canadian population of Slender Yoke-moss is assessed as a single designatable unit.

Special significance

Slender Yoke-moss is known from just one occurrence in North America. It is extremely rare throughout its global range (Schofield 1989, 1990; Ryan 1996; Stebel and Zarnowiec 2017)—despite being abundant at some sites—and has a global conservation ranking of ‘Imperiled’ (G2) (NatureServe 2019). It is a candidate for the forthcoming Red List of Threatened European Bryophytes (Hodgetts 2015).

The species is one of several bryophytes of conservation concern in British Columbia (CESCC 2016; BC CDC 2019) that are thought to have persisted in a coastal refugium during the last glaciation (Schofield 1988).

Distribution

Global range

The global distribution of Slender Yoke-moss has been described as “Western Europe–Western North America” (Golumbia and Bartier 2004). The species is found in Canada; the Yorkshire area of northern England; the Alps (Austria, Germany, Italy, Switzerland), and the western Carpathian Mountains (Poland, Romania, Slovakia) (Figure 1). Outside Canada and England it is regarded as an alpine species (Schofield 1968; Frahm 2012). It was reported from Guatemala (e.g., Vitt 2014), but it has since been confirmed that the specimen was misidentified (Allen 1994). The Canadian population is highly disjunct from the European populations.

Canadian range

The Canadian population of Slender Yoke-moss is located on northeastern Moresby Island on Haida Gwaii (formerly known as the Queen Charlotte Islands), British Columbia, at the site of an abandoned logging camp known as Moresby Camp at the head of Gillatt Arm in Cumshewa Inlet. It has been estimated that the Canadian population accounts for approximately 35% of the global population (CESCC 2016), but that figure seems high considering recent reports documenting its occurrence in several countries in Europe (e.g., Müller 2007; Aleffi et al. 2008; Ştefănuţ and Goia 2012; Hodgetts 2015; Pescott 2016; Stebel and Zarnowiec 2017). A more accurate estimate of the Canadian portion of the global population would be around 10%, based on records from nine countries in Europe (Hodgetts 2015) and Canada.

Extent of occurrence and area of occupancy

Based on the single known subpopulation of Slender Yoke-moss in Canada, the extent of occurrence (EOO) is 4 km². For reference, the substrate on which it occurs—Sadler Limestone—is estimated to cover 54 km² across Haida Gwaii (Figure 2a), very little of which is above ground, near water, unshaded, or occurring as cliffs with a north or northwest aspect.

The index of area of occupancy (IAO) of Slender Yoke-moss in Canada is 4 km² based on a single 2 km x 2 km grid cell.

Search effort

Bryologists have collected widely throughout Haida Gwaii. The archipelago was particularly well-travelled by W.B. Schofield, who spent 16 field seasons on the islands and collected more than 11,000 specimens from 1961–2002 (Schofield 1989; Golumbia and Bartier 2004). Other bryologists and botanists are known to have collected over 2000 additional specimens. In total, bryophytes have been collected from more than 260 sites, including 33 sites associated with limestone deposits. Four sites were searched for the purposes of this report (Table 1).

Schofield (1968) noted that although he had collected bryophytes from limestone substrates throughout Haida Gwaii, he observed Zygodon gracilis at only one place. As further evidence of the species’ rarity and the small size of the subpopulation, only four specimens are known to have been collected by Schofield (three are deposited at UBC and one is at the University of Michigan) compared to multiple collections of other uncommon bryophytes.

Habitat

Habitat requirements

Slender Yoke-moss is a narrow habitat specialist. It occurs exclusively on vertical surfaces of dry outcroppings of highly pure limestone and rock walls consisting of Carboniferous limestone in England. It typically occupies surfaces with north or northwest-facing aspects where it intercepts mist and rain (Porley 2013). In Canada it occupies a cliff face of Sadler limestone (Figure 2a), which comprises massive, thick-bedded grey limestones with very high calcium carbonate (CaCO3) content. Sadler limestone is the only type of pure limestone found on Haida Gwaii and is absent from the mainland coast of British Columbia. Most deposits of Sadler limestone are found in the Coastal Western Hemlock biogeoclimatic zone, but limited quantities are present in the higher-elevation Mountain Hemlock and Alpine Tundra zones.

Habitat trends

Habitat trends have not been studied but limestone deposits outside parks and other protected areas on Haida Gwaii are known to be desirable for industrial purposes. The deposit of Sadler Limestone at Moresby Camp is highly pure and commercially valuable (Tolbert 1987). Although the portion of the cliff face occupied by Slender Yoke-moss is intact, there is ample evidence of disturbance to nearby parts of the outcropping, including disturbed vertical surfaces (likely caused by blasting), heavy-duty cable drape-netting armoring parts of the cliff face, and a large old concrete wall attached to the cliff face. An incredible tangle of industrial cables and pulleys was left behind in the nearby coniferous forest (Appendix 3).

Whereas the moss’s immediate habitat is physically undisturbed, young Sitka Alder (Alnus viridis ssp. sinuata) and Western Redcedar (Thuja plicata) trees have grown up alongside it and are shading the population. Changes to the microclimate may be causing overgrowth of several species of mosses, including Slender Yoke-moss, by cyanobacteria (Nostoc), lichens (including Cladonia and what appears to be Leptogium) and filmy fern gametophytes (Wright’s filmy fern, Hymenophyllum wrightii) (Appendix 3). The cyanobacteria, lichens, and filmy fern were absent from Schofield’s specimens collected in 1961 and 1994.

The trees are young and seem to have become established after the logging camp was abandoned; it is not known whether the area between the cliff face and the ocean was forested before the logging camp was established, but if it was, it is likely that the forest was relatively “open” in character and not densely treed.

Biology

Life cycle and reproduction

Slender Yoke-moss is dioicous (Longton 1992), meaning male and female gametangia occur on separate plants. Populations of the moss at most sites are either male or female. The species has the life strategy of a “perennial stayer” (Hodgetts 1996) (i.e., it is long-lived, expends little if any energy on producing spores or specialized vegetative structures, and occupies a very stable habitat). As previously noted, sexual reproduction has not been observed in Canada and examined specimens are sterile (Schofield 1968). Sporophytes have only been observed twice in England (Longton 1992), first in the mid-1800s and not again until 2002/2003 (Porley 2013), some 140 years later (Bachtold 2003; Pickerell 2003). Sexual reproduction has not been reported from other countries.

Although specialized asexual reproductive structures (protonemal gemmae) have been produced in culture in an ex situ pilot conservation program (Duckett et al. 2004; Rowntree and Rumsey 2005), gemmae have not been observed in the wild. The Canadian population of Slender Yoke-moss consists of a few small colonies which apparently persist through clonal growth. The IUCN has adopted the recommendations of Bergamini et al. (2019), which suggest that for species that are never or rarely observed to produce sporophytes and do not reproduce asexually, generation length be estimated at 33 years.

Physiology and adaptability

Slender Yoke-moss is confined to north- and northwest-facing aspects of limestone cliff faces and rock walls in areas with high humidity and rainfall where it intercepts mist, rain, and fog (Porley 2013). The species’ restriction to these habitat conditions suggests that it has limited desiccation tolerance. Although the physiology and adaptability of the species have not been studied, it is expected that a species occupying such a narrow physiological niche and which has no effective means of dispersal would be unlikely to survive or successfully compete against other species if moisture regimes or intensity and duration of sunlight are altered. Scanty populations in multiple countries (see, e.g., Stebel and Zarnowiec 2017) further suggest the adaptability of the species is extremely low. As noted by Glime (2017), clonal growth habit in mosses has multiple advantages but, in the absence of other means of reproduction, increases the vulnerability of colony-forming species to permanent changes in the environment and to physical disturbance.

Dispersal and migration

Schofield (1989) suggested that the globally disjunct populations of bryophytes on Haida Gwaii may be remnants of an extremely ancient flora, possibly of Tertiary origin, that survived in island refugia but are not expanding in range. Bryophytes typically disperse by wind-blown spores, although alternative means of dispersal do exist. As noted above, spores can only be produced if both sexes are present in proximity, and Slender Yoke-moss produces spores very infrequently or not at all. Sporophytes are not known from Haida Gwaii, nor are gemmae. Therefore, the potential for Slender Yoke-moss to disperse or migrate, even short distances, is extremely low to non-existent.

Interspecific interactions

In northern England, female reproductive structures of Slender Yoke-moss have been damaged by mites (Bachtold 2003). In Canada, interspecific interactions between Slender Yoke-moss and other species have not been documented. However, as previously noted, young trees appear to be affecting light and moisture regimes in the moss’s habitat, which may be facilitating the growth of cyanobacteria.

Population sizes and trends

The single known subpopulation of Slender Yoke-moss in Canada consists of one individual based on the concept of ‘an individual-equivalent’ because the species is known from a single cliff. As outlined by Bergamini et al. (2019) and adopted by the IUCN: “saxicolous taxa growing on cliffs or on other more or less flat surfaces: an ‘individual-equivalent’ = 1 m2 [i.e., 1 m2 in which the taxon occurs, whether as a single ramet or as a dense carpet of many ramets covering most of the surface]”.

The subpopulation was first discovered by Schofield in 1961 and last observed in 2018. Although a small number of specimens have been collected for scientific study, the condition of the population has not been monitored.

Sampling effort and methods

The subpopulation of Slender Yoke-moss at Moresby Camp was relocated by bryologist Wynne Miles in 2018. It is located on a limestone cliff approximately 3 m above ground level.

Abundance

The abundance of Slender Yoke-moss at Moresby Camp was not documented when Schofield collected specimens in 1961, 1966, or 1994. However, the 1966 specimen label notes that the species was “very rare on dry limestone cliff” (Appendix 2). In 1968, Schofield reported in a publication on “mosses of particular interest” in British Columbia that the species was “sterile and extremely rare” (Schofield 1968). The description on the 1994 specimen collection simply states: “black tuft on cliff”. As previously noted, only four specimens of Slender Yoke-moss (including one duplicate) were collected by Schofield, which highlights the rarity of the moss compared to other uncommon species, of which multiple collections were made.

In 2018, the subpopulation of Slender Yoke-moss at Moresby Camp consisted of fewer than ten diffuse colonies of approximately 2 cm2 each, scattered in an area of approximately 1 m2 on a cliff-face.

Fluctuations and trends

There are no estimates of fluctuations and trends in the Canadian population of Slender Yoke-moss. However, several specimens have been collected since 1966 and it is unlikely that the area occupied by the population is expanding given the lack of sexual reproduction and production of gemmae. This speculation is reinforced by the absence of observations of colony-expansion elsewhere (Pressel and Duckett 2004).

Rescue effect

Populations of Slender Yoke-moss in England or central Europe cannot be expected to serve as sources of naturally dispersing propagules because of the long distance between sites and extreme rarity of sexual reproduction (e.g., Longton 1992).

In England, Pressel and Duckett (2004) successfully cultured Slender Yoke-moss in the lab and subsequently reintroduced it to a locality where it was known to occur. It successfully formed healthy colonies but did not produce gemmae or sporophytes and did not colonize adjacent areas.

Threats and limiting factors

Threats

The two greatest known threats to Slender Yoke-moss are quarrying and climate change. The species is also threatened by earthquakes, tsunamis, and problematic native species. In North America it is known from a single occurrence and the entire population consists of one ‘individual equivalent’, making it extremely vulnerable to known threats and unanticipated stochastic events. An IUCN Threats Assessment of Slender Yoke-moss (Appendix 1) resulted in an overall assigned threat assessment of “Very High-Very High” based on the single ‘individual equivalent’ and an assigned generation length of 33 years, with three generations being equal to 100 years (see Bergamini et al. 2019).

Energy production and mining

Mining and quarrying (threat category 3.2)

The population of Slender Yoke-moss on Haida Gwaii is found on a cliff face of a large outcropping of highly pure Sadler limestone (BCGS 2019). The mineral deposit was surveyed as part of City Resources (Canada) Limited’s “Lime Claims” (Tolbert 1987). Although the claim is presently expired, limestone is evidently a desirable commodity as suggested by new claims on Sadler limestone deposits at Tasu. If the claim at Moresby Camp is reinstated or a new claim is made and quarrying proceeds, the entire known population of Slender Yoke-moss and its habitat in Canada and North America would be eliminated. Therefore, in the IUCN Threats Calculator the Scope of the threat is deemed to be “Pervasive”, Severity “Extreme”, and Timing “Moderate–Low”. The overall calculated impact of quarrying on Slender Yoke-moss is “Very High”.

Climate change and severe weather

It is well-established that climate change will impact all biogeoclimatic zones of Haida Gwaii (Banner et al. 2014). Currently the climate in the areas where Slender Yoke-moss occurs at low elevation within the ‘Submontane’ variant of the ‘Wet Hypermaritime’ subzone of the Coastal Western Hemlock zone (CWHwh1) is characterized (as summarized by Banner et al. 2014) by cool, moist summers and mild, wet winters with little snowfall. Mean annual temperature is 7.4°C (ranging from 5.1–9.2°C), mean annual precipitation is 1948 mm (ranging from 1042–5458 mm) and average snowfall is 152 cm, with a record low of 42 cm and a high of 991 cm. Low cloud and fog are common, and relative humidity is typically high throughout the year. Near sea level, where Slender Yoke-moss is found, little precipitation falls as snow and snowpack is ephemeral.

Throughout the Skeena-Queen Charlotte region, it is predicted that mean annual temperature will increase by 1.4 °C from 1961–1990 baseline values by the 2050s, with the greatest increase in temperature occurring in summer (PCIC 2012; Vadenboncoeur et al. 2016). Average annual precipitation is predicted to increase by 7%—which could be construed as a positive change for bryophytes—but the timing and intensity of precipitation events will shift, as will the form of precipitation, with major reductions in snowfall in winter and spring (PCIC 2012; Vadenboncoeur et al. 2016).

Predicting future climate is complicated by two major climatic cycles: the El Niño / La Niña Southern Oscillation (ENSO), which alternates between warm to cold phases every 3–5 years, and the Pacific Decadal Oscillation (PDO) which cycles between warm and cold phases every 40–60 years. Deviations from average values are expected to have major impacts on rare mosses like Slender Yoke-moss, Carey’s Bristle-moss (Seligeria careyana), and Drooping-leaved Beard-moss (Oxystegus recurvifolius), which have very small populations, limited means of dispersal, and occupy a very narrow physiological niches in patchily distributed habitats and therefore could not easily migrate in response to climate change. Species with such characteristics are more vulnerable than most to the ongoing effects of climate change (see Gayton 2008). In the IUCN Threats Calculator, the threat of Climate Change has a Timing of “High”, a Severity of “Extreme”, and the entire population of Slender Yoke-moss will be affected, therefore the Scope is “Pervasive”. The overall Calculated Impact is “Very High”

Habitat shifting and alteration (threat category 11.1)

Habitat-shifting and alteration are occurring on a regional scale throughout coastal British Columbia (Harding and McCullum 1997) and will continue to affect all biogeoclimatic zones on Haida Gwaii (Banner et al. 2014). Owing to the isolation of the archipelago, it is thought that the initial effects of climate change on plants are being expressed as changes in vigour, relative productivity, and reproductive capacity; these are expected to be followed by altered distribution patterns (Banner et al. 2014). The uncertainty of projected climate change is compounded by the complex topography and pronounced ecological gradients on the archipelago (Banner et al. 2014).

The limestone cliff habitat of Slender Yoke-moss is expected to be affected by climate change sooner and more severely than forested habitats. As noted by Porley (2013), in Britain the species was formerly found in relative abundance at both low and high elevation but declines in the subpopulations at low elevation are correlated with statistically significant differences in altitude. This may indicate sensitivity to climate change, given that the average winter temperature in Britain has increased by 0.5 °C over the past century. Although Habitat Shifting has been observed in Masset, it has not been documented at Moresby Camp; therefore, it was not scored in the Threats Calculator.

Droughts (threat category 11.2)

The habitat of Slender Yoke-moss is a limestone cliff in an area that is regularly subject to fog and rain. Altered precipitation regimes in the CWHwh1 as predicted by ClimateBC (Wang et al. 2012) and other information sources for coastal British Columbia (e.g., PCIC 2012) include an overall increase in annual precipitation but a decrease in rainfall during summer and a decrease in precipitation falling as snow, particularly in winter and spring.

If rainfall decreases and causes prolonged drought, the moss would likely be exposed to microclimatic conditions outside its range of desiccation tolerance, causing physiological stress or possible death. In the IUCN Threats Calculator, the Timing of Droughts was deemed to be “High (Continuing)”; the Severity “Extreme-Moderate”, reflecting some uncertainty; and the Scope “Pervasive”, because the threat will affect the entire population. Overall, Droughts have a Calculated Impact of “Very high–Medium”.

Temperature extremes (threat category 11.3)

Although there are no known studies demonstrating the tolerance of Slender Yoke-moss to temperature extremes, its occurrence solely in oceanic and mountainous climates suggest that it would not tolerate high temperatures. As with Droughts, the Timing of Temperature Extremes is scored “High (Continuing)”; the Severity “Extreme–Moderate”; and the Scope “Pervasive”. The Calculated Impact is “Very high–Medium”.

Geological events

Earthquakes and tsunamis (threat category 10.2)

The population of Slender Yoke-moss at Moresby Camp will likely be inundated by seawater in the event of a major tsunami (see Rabinovich et al., 2019), although the effects of inundation by seawater are unknown and there is no evidence that the site has been inundated in recent years. The population is located at the head of Cumshewa Inlet very close to the shoreline (<10 m) and near sea level (<10 m). Strong earthquakes are common on the Queen Charlotte Fault and have caused occasional tsunamis (Bevington et al. 2017). Furthermore, the threat of tsunamis will be exacerbated by future sea level rise, which at Prince Rupert on the mainland coast is projected to increase between 0.10–0.31 m (based on extreme low estimates of global sea level rise) and 0.95–1.16 m (based on extreme high estimates) by 2100 (Bornhold 2008; and see Thomson et al. 2008 for further discussion). The Timing of the threat is scored as “High–Low”, the Scope “Pervasive”, and the Severity “Serious”, with an overall Calculated Impact of “High”.

Invasive and other problematic species and genes

Invasive non-native / alien species (threat category 8.1)

When sporophytes of Slender Yoke-moss were found in northern England in 2003, Headley and Rumsey observed damage to female reproductive organs (archegonia) caused by mites (Bachtold 2003; Porley 2013). Bachtold (2003) reported that the researchers would write an article on the topic, but to date, it does not appear to have been published. Mites have not been observed on the specimens of Slender Yoke-moss from Moresby Camp and are therefore not included in the Threats Calculator.

Problematic native species / diseases (threat category 8.2)

Native Sitka Alder (Alnus viridus ssp. sinuata) and Western Redcedar (Thuja plicata) trees have become established immediately alongside the cliff face where Slender Yoke-moss occurs (see Appendix 3). The trees currently cast shade on the moss population and may be facilitating abundant growth of cyanobacteria on multiple species of mosses, including Slender Yoke moss. Future research may illuminate the extent to which the trees are affecting on environmental conditions such as light, temperature, humidity, and air flow. Currently the Timing of the threat is scored as “High-Continuing”, with Severity ranked as “Extreme-Serious” to reflect uncertainty until the population can be more closely examined, and Scope as “Pervasive”. The Calculated Impact is “Very High-High”.

Human intrusions and disturbance

Work and other activities (threat category 6.3)

As early as 1966, Schofield noted that Slender Yoke-moss was very rare at Moresby Camp. Unless researchers and conservation practitioners take extreme care to avoid over-collecting for research (e.g., for DNA analyses) and damaging the population while monitoring it, the Canadian population of Slender Yoke-moss will be adversely impacted. In the Threats Calculator the timing was determined to be “High (Continuing)” because the moss is expected to be studied in the near future; the Severity is scored as “Negligible” because it is hoped that care will be taken to limit adverse effects; and the Scope is “Pervasive” because the entire population is subject to the threat. The calculated impact is “Negligible”.

Transportation and service corridors

Roads and railroads (threat category 4.1)

The large outcropping of limestone at Moresby Camp is located near the end of a narrow, abandoned road or track, fewer than 10 metres from the ocean shore. In 2017 and 2018 flagging-tape indicating road-widening was attached to a nearby outcropping. However, there are apparently no known plans for roadwork to proceed (B. Wijdeven, pers. comm. 2018). Therefore, Roads was not included in the Threats analysis.

Limiting factors

Slender Yoke-moss is limited by several factors including extreme rarity of reproduction, high habitat specificity, and a globally disjunct pattern of distribution (Porley 2013). In the British Isles the extant population is composed of numerous colonies occurring within a single hectad (an area of 10 km x 10 km). The species is dioicous and most colonies consist of either males or females. Vegetative reproduction has not been observed outside the laboratory.

Slender Yoke-moss is an example of Longton and Hedderson’s (2000) model of rare bryophytes constrained by habitat rarity and a narrow range of climatic conditions (Söderström 2006; Porley 2013). In Britain, the species occurs primarily on north- and northwest-facing vertical surfaces of dry Carboniferous limestone (including rock walls) where it intercepts rain and mist (Porley 2013) and presumably stays moist for longer periods of time than it would on southern-facing surfaces. In Canada, Slender Yoke-moss occurs within a temperate climate zone on a limestone cliff that is similarly north-facing and intercepts rain and fog.

Number of locations

The number of locations of Slender Yoke-moss in Canada is one because there is only one known occurrence. Haida Gwaii is among the most well-explored regions in Canada for bryophytes, but despite extensive collecting throughout the archipelago and targeted searches for the species, it has nevertheless been found at only one site.

Protection status and ranks

Legal protection and status

Slender Yoke-moss is not protected under Canada’s Species at Risk Act (SARA), the British Columbia Wildlife Act, or any other legislation (BC CDC 2019).

Non-legal status and ranks

The global conservation status of Slender Yoke-moss is G2, “Imperiled” (NatureServe 2019), and its status in Canada is N1, “Critically Imperiled” (CESCC 2016). In British Columbia its status is S1S2, “Critically Imperiled” (BC CDC 2019), but it was reported as S1 by the Canadian Endangered Species Conservation Council (CESCC 2016). It is included on the province’s “Red List” (BC CDC 2019).

Zygodon gracilis is a candidate for the forthcoming Red List of Threatened European Bryophytes (Hodgetts 2015). As reported by Hodgetts (2015) it is “Critically Endangered” in Slovakia; “Endangered” in Great Britain, Italy, and Poland; and “Vulnerable” in Switzerland. In Austria it has been designated as “Risk Assumed”, whereas in Germany its status is “Extremely Rare”. The species is confirmed from France although its current status is unknown, and it is “Regionally Extinct” in Romania. In 2017 Stebel and Żarnowiec assessed Z. gracilis as “Critically Endangered” in Poland.

Habitat protection and ownership

The only known location of Slender Yoke-moss in Canada is at Moresby Camp at the head of Gillatt Arm in Cumshewa Inlet on Moresby Island. It is on Crown land and is not protected.

Acknowledgements and authorities contacted

This report was funded by Environment and Climate Change Canada with additional financial resources contributed by the British Columbia Conservation Centre and the Smithsonian Institution through a Smithsonian Global Genome Initiative grant to G.K. Golinski (GGI-Rolling-2017-157). Any opinions, findings, and conclusions or recommendations expressed in this report belong to the author and do not necessarily reflect the views of the Global Genome Initiative.

The report writer acknowledges the assistance of the COSEWIC Mosses and Lichens Subcommittee and the COSEWIC Secretariat, particularly Angèle Cyr, Jenny Wu, Sonia Schnobb, and Shirley Sheppard. The following individuals kindly contributed to this report in a variety of ways, including information-sharing, loans of specimens, logistics, permit approvals, fieldwork, and reviews.

Authorities contacted

René Belland, COSEWIC and Faculty Service Officer, Department of Renewable Resources, University of Alberta, Edmonton, AB

Carita Bergman, Gwaii Haanas National Park Reserve and Haida Heritage Site, Skidegate, British Columbia

Ruben Boles, Canadian Wildlife Service, Gatineau, QC

Neil G. Carey, Sandspit, British Columbia

Stu Crawford, Haida Fisheries, Masset, British Columbia

Marta Donovan, British Columbia Conservation Data Centre, Victoria, British Columbia

Joy Golinski, Campbell River, British Columbia

Spencer Goyette, University of Alberta, Edmonton, Alberta

Eric Gross, Canadian Wildlife Service, Pacific Region

Sybille Haeussler, Bulkley Valley Research Centre, Smithers, British Columbia, and University of Northern British Columbia, Prince George, British Columbia

Judith Harpel, University of British Columbia Herbarium (UBC), Vancouver, British Columbia

Kristian Hassel, NTNU, Trondheim, Norway

Neil Jones, COSEWIC Secretariat, Canadian Wildlife Service Environment Canada, Gatineau Quebec

Olivia Lee, University of British Columbia Herbarium (UBC), Vancouver, British Columbia

Will Mackenzie, British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development, Smithers, British Columbia

Wynne Miles, Bryologist, Victoria, British Columbia

Jenifer Penny, British Columbia Conservation Data Centre, Victoria, British Columbia

Jim Pojar, Smithers, British Columbia

Peter Sinkins, Gwaii Haanas National Park Reserve and Haida Heritage Site, Skidegate, British Columbia

Lucy Stefanyk, British Columbia Ministry of Environment, Queen Charlotte, British Columbia

Berry Wijdeven, British Columbia Ministry of Forests, Lands and Natural Resource Operations, Queen Charlotte, British Columbia

Patrick Williston, British Columbia Ministry of Environment, Smithers, British Columbia

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Biographical summary of report writers

G. Karen Golinski is a Research Associate in the Department of Botany at the Smithsonian Institute and an Honorary Research Associate in the Department of Botany at the University of British Columbia. Her research focuses on the biodiversity and conservation of bryophytes. Karen received her PhD from the University of Victoria in 2004 and was a Postdoctoral Research Fellow in the Center for Conservation and Sustainability at the Smithsonian Institution from 2014–2016. She has been a member of the British Columbia Bryophyte Recovery Team since 2005, the Mosses and Lichens Species Specialist Subcommittee of COSEWIC since 2012, and the IUCN Species Survival Commission Bryophyte Specialist Group since 2019.

Collections examined

Three specimens of Slender Yoke-moss were borrowed from the University of British Columbia (UBC) and examined:

1. Cumshewa Inlet, NW coast of Moresby Island, Queen Charlotte Islands, Dry marble cliff, August 25, 1961, 24/08/1961, Coll. W.B. Schofield #15517, Det. H. Person (?) (UBC B145602)
2. Moresby Logging Camp, Gilliatt (sic) Arm, Cumshewa Inlet, Moresby I., Queen Charlotte Islands, 50° 03′ N, 132° 01′ W, Very rare in dry limestone cliff, July 21, 1966, W.B. Schofield #32063 (UBC B145603)
3. Queen Charlotte Is., Moresby I., Moresby Campsite, Cumshewa Inlet head, limestone cliff near shore, Black tuft on cliff, June 28, 1994, W.B. Schofield #100935 (UBC B15498)

A duplicate of a specimen collected by Schofield, #32062, held by the University of Michigan but with a different date (July 31, 1966), was annotated by Dale H. Vitt (1-69): “Compares well with European material”.

Appendix 1. IUCN threats calculator for Slender Yoke-moss (Zygodon gracilis).

Threats assessment worksheet

Species or ecosystem scientific name:

Slender Yoke-moss (Zygodon gracilis)

Element ID:

122728

Elcode:

NBMUS7Z030

Date:

5/4/2018

Assessor(s):

Author: G. Karen Golinski; SSC: Jennifer Doubt, Nicole Fenton, Chris Lewis, Richard Caners, Rene Belland; BC: Brenda Costanzo, Dave Fraser; CWS: Ruben Boles; Facilitator: Dwayne Lepitzki

References:

Not applicable

Assigned overall threat impact:

A = Very High

Impact adjustment reasons:

No adjustment: the species is known from a single location in Canada and North America and is globally rare.

Overall threat comments:

Generation time is 33 years. Threats calculator based on a single unprotected site on Crown land.
Note that the threat teleconference occurred In 2018 but was subsequently revised to reflect the new definition of "individual" based on Bergamini et al. (2019) and the Impact of Problematic native species/diseases was increased based on comparison of older and recent specimens.

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

Appendix 2. Photographs of the UBC herbarium specimens of Slender Yoke-moss (Zygodon gracilis). Photographs by Karen Golinski.

Appendix available upon request.

Appendix 3. a) Habitat of Slender Yoke-moss (Zygodon gracilis), Moresby Camp (left part of photo); b) potential habitat, east Limestone Island; disturbance and threats to Slender Yoke-moss at Moresby Camp: c) disturbed cliff face and concrete wall; d) drape-netting armoring; e) flagging tape (centre of photo) indicating future roadwork; f) cyanobacteria overgrowing moss. Photographs by Karen Golinski.