Scaly Fringe Lichen (Heterodermia squamulosa): COSEWIC assessment and status report 2022

Official title: COSEWIC Assessment and Status Report on the Scaly Fringe Lichen (Heterodermia squamulosa) in Canada 2022

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

COSEWIC assessment summary

Assessment summary – December 2022

Common name: Scaly Fringe Lichen

Scientific name: Heterodermia squamulosa

Status: Threatened

Reason for designation: Within Canada, this lichen only occurs only in Nova Scotia and New Brunswick on old undisturbed hardwood or mixedwood forests without signs of past forest harvesting. The small Canadian population (less than 550 thalli on 145 known host trees) is projected to decline as a result of threats. These include forest harvesting, road construction, and residential development that lead to the loss of host trees or open the forest canopy that makes the habitat unsuitable for the lichen. In addition, air pollution, and the Emerald Ash Borer are other factors that are likely to contribute to the projected decline.

Occurrence: New Brunswick, Nova Scotia

Status history: Designated Threatened in December 2022.

COSEWIC executive summary

Scaly Fringe Lichen
Heterodermia squamulosa

Wildlife species description and significance

Scaly Fringe Lichen (Heterodermia squamulosa) is a rare lichen that grows on the bark of hardwood trees in old forests, which are now rare in Atlantic Canada. This leafy lichen usually has small pale grey lobes and numerous upright lobules. The disc-shaped fruiting bodies (apothecia) have only been found once in Canada and once in the USA, being extremely rare in North America.

Aboriginal (Indigenous) Knowledge

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

Distribution

Scaly Fringe Lichen has a disjunct global distribution across North, Central and South America, and also occurs in Africa and Asia. The global population is primarily concentrated in the southern and central Appalachians of the USA. In Canada, this lichen is at the northern, colder limit of its range. It is found mainly in Nova Scotia but is also known in New Brunswick.

Habitat

In Canada, Scaly Fringe Lichen is only found within 50 km of the coast and lives almost exclusively in old hardwood or mixedwood forest with no obvious signs of past forest harvesting. It is found on living Yellow Birch, Sugar Maple, Red Maple, and White Ash trees that grow on reasonably nutrient-enriched soils in both wetland and upland habitats.

Biology

Lichens are symbiotic organisms, formed by the association of a fungus and a photosynthetic green alga or cyanobacterium. Scaly Fringe Lichen is a symbiosis between the Heterodermia squamulosa fungus and Trebouxia, a green alga. The generation time for Scaly Fringe Lichen individuals is thought to be 19 years. The lichen’s primary means of reproduction is by vegetative lobules, which are relatively heavy, or thallus fragments, which means that dispersal is mostly limited to short distances (i.e., within a forest stand). The species very rarely forms fruit bodies in North America.

Population size and trends

Scaly Fringe Lichen occurs in Nova Scotia and New Brunswick, where 31 occurrences have been found. These occurrences form 14 subpopulations. The enumerated population is 515 thalli growing on 145 trees. The occurrence at Cape Split (Scots Bay subpopulation) comprises approximately 50% of all the known thalli on about 50% of the colonized host trees. While more than 73 previously-undocumented thalli and 31 previously-unknown host trees were discovered in the extensive 2019-2020 surveys that were done in association with this report, the total known number of thalli is still small. The total population in Canada is estimated to be fewer than 1000 thalli. Overall, as a result of the threats described below, the population appears to be in decline at sites where re-measurements exist.

Threats and limiting factors

The main threats to Scaly Fringe Lichen are the harvesting of host trees and the construction of roads leading to habitat disruption. Other threats that affect the Scaly Fringe Lichen or its host trees include climate change, air pollution (particularly acid rain), the invasive Emerald Ash Borer, and land development. The limiting factors for this lichen include short dispersal distance, a limited amount of suitable habitat and being, in Canada, at the northern edge of its climatic and geographic range.

Protection, status, and ranks

Scaly Fringe Lichen has a global rank of G3G5 (Vulnerable to Secure), a national rank of N3 (Vulnerable), a New Brunswick rank of S1 (Critically Imperiled), and a Nova Scotia rank of S3 (Vulnerable). It has a status of SNR (unranked) in Quebec, where the lichen was reported in the past, based on an incorrectly identified specimen that was a different species. Approximately 32% of Scaly Fringe Lichen host trees in Canada currently occur within protected areas.

Technical summary

Scientific name: Heterodermia squamulosa
English name: Scaly Fringe Lichen
French name: Hétérodermie squamuleuse
Range of occurrence in Canada: New Brunswick, Nova Scotia

Demographic information

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

19 years (see Biology – Life Cycle and Reproduction)

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

Yes, inferred and projected; on the basis of declines in host trees mainly as a result of forest harvesting (see Fluctuations & Trends; Threats).

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

Data are not available to estimate, with confidence, the percentage decline in the number of mature individuals. However, the decline is estimated to be about 18% over 5 years (see Fluctuations and Trends).

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

Uncertain, but the decline based on the reduction in colonized trees over the last 10 years is estimated to be 36% (see Fluctuations and Trends).

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

A projected decline over three generations is > 50% based on the projected reduction in number of colonized host trees over next 57 years (see Fluctuations and Trends).

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

Observed and inferred reduction over the past 10 years and projected for a further two generations is > 50% (see Fluctuations and Trends).

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

a. No, not in the short term, unless logging is curtailed.
b. Yes, most causes are understood.
c. No, not all causes have ceased.

Are there extreme fluctuations in number of mature individuals?

No

Extent and occupancy information

Estimated extent of occurrence (EOO)

33,848 km² (~8,000 of this is ocean)

Index of area of occupancy (IAO) (Always report 2x2 grid value).

120 km²

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

a. Unknown.
b. Yes, very likely.

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

29 based on stand related threats.
(31 known occurrences, but two are no longer extant; see Number of Locations.)

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

Yes, observed and projected decline based on loss of occurrences in NB has made the EOO smaller.

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

Yes, observed and projected decline in index of area of occupancy based on loss of occurrences in NB, and projected declines in colonized host trees.

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

Yes, projected, as four of 14 subpopulations have < 10 mature individuals and face forestry and other threats and there has been a loss of the Grand Bay-Westfield occurrence.

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

Projected, based on threats and observed losses.

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

Yes, there is an observed and projected reduction in area, extent and quality of habitat.
(See Habitat.)

Are there extreme fluctuations in number of subpopulations?

No

Are there extreme fluctuations in number of locations*?

No

Are there extreme fluctuations in extent of occurrence?

No

Are there extreme fluctuations in index of area of occupancy?

No

^* See COSEWIC definitions and abbreviations on website for more information on this term.

Number of mature individuals (in each subpopulation)

Quantitative analysis

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

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

Was a threats calculator completed for this species? Yes.

Overall threat impact was high

• 4. Transportation and Service: Road Building: medium impact (4.1 Roads and railroads)
• 5. Biological Resources: Logging and Wood Harvesting: medium impact (5.3 Logging and wood harvesting)
• 9. Pollution: Acid Rain: medium-low impact (9.5 Air-borne pollutants)
• 1. Residential and Commercial Development: low impact (1.1 Housing and urban area)
• 7. Natural System Modifications: fires and deer: low impact (7.1 Fire and fire suppression)
• 8. Invasive and Problematic Species: low impact (8.1 Invasive non-native/alien species/diseases)
• 11. Climate Change and severe weather: unknown impact

What additional limiting factors are relevant?

• Limited dispersal via thallus lobules
• Northern edge of the range of this lichen

Rescue effect (immigration from outside Canada)

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

The Canadian population is ~100 km from the nearest next occurrence in Maine, where it is reported to be rare.

Is immigration known or possible?

Highly unlikely; short-distance dispersal is the norm for this lichen.

Would immigrants be adapted to survive in Canada?

Probably

Is there sufficient habitat for immigrants in Canada?

Probably, but only if forestry activity is reduced.

Are conditions deteriorating in Canada?⁺

Probably, but only if forestry activity is reduced.

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

Yes (see Habitat).

Is the Canadian population considered to be a sink?⁺

No

Is rescue from outside populations likely?

Highly unlikely.

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

Data sensitive species

Is this a data sensitive species? No

Status history

COSEWIC: Designated Threatened in December 2022.

Status and reasons for designation

Status: Threatened

Alpha-numeric codes: C2a(i); D1

Reasons for designation: Within Canada, this lichen only occurs only in Nova Scotia and New Brunswick on old undisturbed hardwood or mixedwood forests without signs of past forest harvesting. The small Canadian population (less than 550 thalli on 145 known host trees) is projected to decline as a result of threats. These include forest harvesting, road construction, and residential development that lead to the loss of host trees or open the forest canopy that makes the habitat unsuitable for the lichen. In addition, air pollution, and the Emerald Ash Borer are other factors that are likely to contribute to the projected decline.

Applicability of criteria

Criterion A (Decline in Total Number of Mature Individuals): May be close to meeting the threshold for Endangered, A3acde, as there is a suspected reduction in the total population over the next three generations, but there is current uncertainty as to the magnitude of the projected decline.

Criterion B (Small Distribution Range and Decline or Fluctuation): Not applicable. The IAO is 120 km², but EOO exceeds 20,000 km², and there are > 10 locations. Although there is a projected decline in the population, the species is not severely fragmented and does not experience extreme fluctuations in IAO, EOO, locations, subpopulations or number of individuals.

Criterion C (Small and Declining Number of Mature Individuals): Meets Threatened, C2a(i), as there are < 10,000 mature individuals and no subpopulation has > 1000 individuals. In addition, there is an inferred and projected decline in the number of mature individuals.

Criterion D (Very Small or Restricted Population): Meets Threatened, D1, as the population is estimated to be < 1000 mature individuals.

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

COSEWIC history

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

COSEWIC mandate

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

COSEWIC membership

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

Definitions (2022)

Wildlife species

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

Extinct (X)

A wildlife species that no longer exists.

Extirpated (XT)

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

Endangered (E)

A wildlife species facing imminent extirpation or extinction.

Threatened (T)

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

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

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

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

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

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

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

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

Wildlife species description and significance

Name and classification

Scientific Name: Heterodermia squamulosa (Degel.) W.L. Culb.
Original Description: Anaptychia squamulosa Degel.
Synonyms (GBIF 2020, Mongkolsuk et al. 2015):
Polyblastidium squamulosum (Degel.) Kalb
Anaptychia squamulosa Degel.
English vernacular name: Scaly Fringe Lichen
French vernacular name (Fournier 2006): Hétérodermie squamuleuse
Aboriginal names: [unknown in Canada]
Genus: Heterodermia
Family: Physciaceae
Order: Caliciales
Class: Lecanoromycetes
Phylum: Ascomycota
Kingdom: Fungi

Morphological description

Heterodermia squamulosa (Scaly Fringe Lichen) is a pale-grey to blue-grey foliose lichen (Hinds and Hinds 2007; Lendemer 2009). Thalli typically reach 5 to 12 cm in diameter, while lobes are 0.2 to 1.2 mm wide. Fine, often upright lobules (phyllidia/squamules) usually populate the lobes, especially near the thallus center. Tips or entire lobules can break down or develop into tiny squamules. The medulla is white, and the underside is purple pigmented centrally and lacks a cortex, while the rhizines are dark, squarrose or tufted and located along lobe margins (Brodo et al. 2001).

Apothecia on H. squamulosa have not been found in North America (Brodo et al. 2001; Moberg 2011), except for one specimen from Giles County, Virginia, USA, (Culberson 223954 Duke) and one recent find in Digby County, Nova Scotia, Canada, by Alain Belliveau (see left centre of cover photo). However, in South Korea, apothecia are more common, occurring on the surface of the lamina and being sessile, dark reddish brown, and 1–4 mm in diameter (Wang et al. 2008). This description matches that of the apothecia recently found in Nova Scotia.

Heterodermia squamulosa is the only member of the genus in eastern North America that disperses almost exclusively via lobules or thallus fragments (see Life Cycle and Reproduction). Fruit bodies (apothecia) have only been found once in Canada (see above). Their absence makes this species more easily identified in the field. Immature or damaged specimens can lack lobules, but in such cases the ecorticate and purple-pigmented undersurface, as well as chemistry, can be used for identification.

The photobiont partner of H. squamulosa is a species of Trebouxia(Trebouxiophyceae) green alga (Brodo et al. 2001; Nash et al. 2002; Hinds and Hinds 2007).

Chemistry

Secondary metabolites of H. squamulosa include atranorin, zeorin, leucolytin, and norstictic acid (Lendemer 2009). Atranorin in its cortex results in a yellow reaction with a spot test of K (potassium hydroxide) and with PD (para-phenylenediamine). The zeorin and other terpenoids found in the medulla can be detected with thin layer chromatography (TLC). All other standard diagnostic spot tests and UV reactions are negative.

Population spatial structure and variability

Heterodermia squamulosa is known in Canada from southern New Brunswick and mainland Nova Scotia. To date, 31 occurrences (see Canadian Range) are known (Table 1). Approximately 95 km is the largest gap between two adjacent occurrences in Canada, with all other occurrences being within 60 km of another (AC CDC 2020).

Outside of Canada, the nearest occurrences are in Maine, USA, (Figure 1) where only five occurrences are known (Hinds and Hinds 2007; Seaward et al. 2017; Hinds 2020). The nearest of these Maine occurrences, on Roque Island, is about 100 km from the occurrence in Welsford, New Brunswick. There is also one occurrence in New Hampshire, USA, (Clyne 246-16 CUP; Cleavitt pers. comm. 2020), with the next closest site being in Pennsylvania, USA, (Lendemer 37763 NY), approximately 500 km away from the New Hampshire site and 950 km away from Canadian occurrences.

Designatable units

The Canadian population is considered a single designatable unit because there are no known biological or other differences between occurrences that might reflect historical or genetic distinctions (see Population Spatial Structure and Variability).

Special significance

Heterodermia squamulosa is part of a group of lichen species with a strong Appalachian distribution or a strictly Appalachian biogeographical affinity (Hinds and Hinds 2007; Clayden 2010). They include Anaptychia palmulata (S3S4 / Vulnerable in both NB and NS), Heterodermia neglecta (S4 / Apparently Secure in NB, S3S4 / Vulnerable in NS), Punctelia appalachensis (S1 / Critically Imperilled in NB, S3 / Vulnerable in NS), and Rinodina ascociscana (not ranked in NB, S4 / Apparently Secure in NS; AC CDC 2020; CNALH 2020). Several members of this group reach eastern Canada (see Distribution – Global Range) and co-occur with H. squamulosa in New Brunswick and Nova Scotia, often on the same tree or on neighbouring trees. Compared with these lichens, H. squamulosa has the fewest known occurrences, being restricted to New Brunswick and Nova Scotia. It is an indicator of undisturbed habitat within cool, temperate, hardwood or mixedwood, and mature to old forests (see Habitat – Habitat Requirements).

In New Brunswick and Nova Scotia, H. squamulosa occurs in, and indicates, old undisturbed forest, an increasingly rare forest type in Atlantic Canada (Loo and Ives 2003). Its preferred habitat of mature to old hardwood or mixedwood forest is home for other at-risk species, such as Pectenia plumbea(formerly Degelia plumbea: Special Concern; COSEWIC 2010) and Eastern Wood-pewee (Contopus virens, Special Concern (COSEWIC 2012).

Aboriginal (Indigenous) Knowledge

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

Cultural significance to Indigenous peoples

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

Distribution

Global range

Heterodermia squamulosa has been reported from North, Central, and South America, western Africa, and eastern Asia (CNALH 2020). In North America (Figure 1), it has been reported from eastern Canada and eastern United States (Georgia, Kentucky, Maine, Maryland, New Hampshire, North Carolina, Ohio, South Carolina, Tennessee, Virginia, and West Virginia) and in western United States (Arizona and Utah) (CNALH 2020). In South and Central America, H. squamulosa has been reported from Argentina, Brazil, Costa Rica, Dominican Republic, Ecuador, Haiti, Mexico, Peru, Uruguay, Venezuela, and French Guiana. It is also known from South Korea, Japan, and Guinea (Wang et al. 2008; Moberg 2011; Sarlej 2018; CNALH 2020).

Canadian range

Heterodermia squamulosa is found in coastal forests of the Atlantic Maritime Ecozone, disjunct from its core North American Appalachian mountain range (Clayden 2010). In Canada, it is known only from New Brunswick and Nova Scotia (Figure 2). All 31 known occurrences are within 50 km of the coast and are most frequent along or near the Bay of Fundy, becoming increasingly sparse going eastward along Nova Scotia’s south and eastern shores. There is a correlation between the occurrence of H. squamulosa and the areas of the province that support an exceptionally high diversity of lichens (Cameron and Bayne 2020). The one collection from Quebec (Lutzoni 840718-L138 QFA) was examined for this report and proved to be a different species, likely H. neglecta or H. galactophylla (Anderson pers. comm. 2020).

An occurrence is defined as a site where the lichen is growing on one or more trees and is separated by more than 1 km from a second group of colonized trees (see NatureServe 2020). Seven occurrences have been documented in New Brunswick, but two were not confirmed in the recent field verifications. One other occurrence was likely confirmed in a recent survey, although there was uncertainty about the original coordinates. Another could not be confirmed, mostly due to geographic uncertainty, and a final occurrence with some uncertainty was found and has been added to this report (Table 1).

The occurrences are grouped into 14 subpopulations,12 in Nova Scotia and two in New Brunswick (Figure 2), of which one (NB 01) may no longer be extant (Figure 2). Subpopulations are defined as geographically or otherwise distinct groups, between which there is little demographic or genetic exchange, typically one successful migrant individual or gamete per year or less (IUCN 2019). The subpopulations are separated from one another by a distance that is greater than 15 km, a distance that likely exceeds the dispersal of its heavy propagules. In Canada, this lichen has only once been found fertile (see Dispersal and Migration).

No genetic analyses have been done to assess the degree of relatedness among occurrences or subpopulations. The occurrences were grouped into subpopulations that are separated by relatively small distances. This was justified by the fact that Heterodermia squamulosa reproduces almost exclusively, in Canada, by means of lobules (see Dispersal).

The recent discovery of apothecia (sexual reproduction) on a specimen in Digby County, Nova Scotia, suggests that the capacity for genetic diversity among sites may be higher than previously thought. In the past, apothecia may have been formed more often on thalli when habitats and environmental conditions were more favourable.

Extent of occurrence and area of occupancy

The calculated extent of occurrence (EOO) is 33,848 km², and the index of area of occupancy (IAO) is 120 km² (see Figure 3). The oceanic part of the EOO represents c. 8000 km². There has been an observed decline in IAO based on loss of occurrences in New Brunswick and Nova Scotia between 2006 and 2007, when the species was first observed there, and 2019, when the most recent surveys occurred.

Search effort

Since 2007, targeted lichen surveys extending over 2,000 km of track distance (average of 20–50 m wide band captured, for a total area surveyed of 4,000–10,000 ha) have been carried out. As a pre-condition for forestry activity on public land in Nova Scotia, a survey is carried out to detect and monitor the occurrence of Boreal Felt Lichen (Erioderma pedicellatum) as a result of a provincial management policy (COSEWIC 2014; Belliveau and McMullin 2017; Brad Toms pers. comm. 2020). Although surveys target habitat suitable for E. pedicellatum, surveyors actively record lichens outside of those areas, including habitat suitable for H. squamulosa (AC CDC 2020). Some of the surveys occurred in close proximity (<10 km) to known H. squamulosa occurrences. The lichens recorded by surveyors included H. squamulosa and associated species such as Anaptychia palmulata, H. neglecta, and Pectenia plumbea (see Habitat – Habitat Requirements), indicating that surveyor proficiency was sufficient to detect H. squamulosa. Despite the extensive searches, only one occurrence (Spider Lake) of H. squamulosa was found.

Another method for assessing search effort is to map occurrences of species that are visually or ecologically similar to the focal species (Ponder et al. 2001; Phillips et al. 2009). In the Atlantic Region, the target group for H. squamulosa includes other members of the genus Heterodermia, as well as Punctelia appalachensis and A. palmulata, which are visually similar and occur in the same habitat. There are over 500 records of this target group (Figure 4) available from the Consortium of North American Lichen Herbaria and the Atlantic Canada Conservation Data Centre databases, and even more records from a local personal herbarium with unpublished collections (F. Anderson pers. comm. 2021). Despite this widespread search effort, H. squamulosa has been found infrequently, and only in certain regions. The historical and more recent herbarium records of known lichen associates of H. squamulosa provide a good indication of the likely limits of its distribution.

Recent searches

Sites were searched in 2019 and 2020 specifically for H. squamulosa, and the finds have been grouped into a total of 16 occurrences (Table 1). The Lac de l’École occurrence was not surveyed because of the high geographic uncertainty of the original record. This also applied to the Maple Grove occurrence, and so only a partial survey was done there. The Goose River occurrence was not surveyed because of its remoteness, but an area adjacent to it was searched opportunistically. In 2020, several lichen surveyors in both provinces surveyed areas that had potentially suitable habitats, or paid particular attention to areas with potential habitats while conducting other fieldwork. Several occurrences were more extensively surveyed in 2020 to provide further data for this report. These included surveys of areas immediately adjacent to or nearby known occurrences that appeared to have potential for suitable habitat, based mostly on forest cover as observed in various satellite imagery. The Loch Alva occurrence was added in 2022 after a recent survey.

^*SC = Stephen Clayden, DS = Dwayne Sabine, AGB = Alain G. Belliveau, NV = Neil Vinson, CC = Colin Chapman-Lam, JLC = James L. Churchill, TN = Tom Neily, HC = Harold Clapp, JR = Jonathan Riley, ICB = Ian C. Bryson, FA = Frances Anderson.

A Maxent species distribution model (Phillips et al. 2019) was developed for H. squamulosa in Nova Scotia to help guide field survey efforts for this Status Report (Haughian et al. 2019). The initial model included known, spatially-precise occurrences and a suite of environmental variables known to be important to the species, which described climate, forest stand structure, disturbance, soils, topography, and hydrology. A backwards-stepwise selection process was used to find the most parsimonious model of the distribution of suitable conditions for the species in Nova Scotia. The final model had an AUC of 0.913 (suggesting the model fit the data well) and included five variables: estimated acid critical threshold exceedance (from Moran et al. 2008), mean annual daily standard deviation in temperature, distance to nearest waterbody, forest structure (minimum forest height of 10 m and crown closure > 30%), and mean number of days with rainfall > 0.2 mm.

Despite the model being limited by the quality of available geographic information systems (GIS) data, four medium-to-high probability sites in Digby and Kings counties in Nova Scotia were identified and visited in 2019. However, no new occurrences of H. squamulosa were found, and no strongly associated indicator lichen species (see Habitat – Habitat Requirements) were discovered (see Population Sizes and Trends – Abundance).

In addition to the lichen surveys mentioned above, other unpublished searches have been conducted specifically within the distribution range of H. squamulosa in New Brunswick and Nova Scotia by the surveyors listed in the legend of Table 1. They surveyed an estimated minimum of 100 km of track distance (average of 20–50 m wide band captured, for a very conservative total area surveyed of 200–500 ha). These surveys occurred through work-related or personal volunteer efforts, and approximately eight of 11 surveyors live in and/or work in areas known to have occurrences or areas with especially high potential for suitable H. squamulosa habitat. Survey efforts for lichens in New Brunswick are generally lower than in Nova Scotia and in New England. Therefore, information from those adjacent jurisdictions was used to help with New Brunswick assessments including lichen abundance estimates using the species distribution model.

Habitat

Habitat requirements

Heterodermia squamulosa requires mature to old hardwood or mixedwood forest dominated by long-lived, shade-tolerant tree species. Sites typically include nutrient-enriched soils and are within 50 km of the coast. The majority of occurrences are in hardwood-dominated forests, while mixedwood and softwood-dominated forests account for five and only one occurrence, respectively. The most frequent dominant and co-dominant tree species observed in at least six occurrences of an H. squamulosa habitat are: Yellow Birch (Betula alleghaniensis), Sugar Maple (Acer saccharum), Red Maple (Acer rubrum), and White Ash (Fraxinus americana).

The climate in southern New Brunswick and Nova Scotia is temperate, with a blending of continental and maritime influences. The proximity of all known occurrences to the ocean (<50 km) suggests that habitat requirements include fog, cooler warm season temperatures, and greater annual precipitation. In New England, higher-elevation forests appear to provide some of these same habitat characteristics at sites that are further inland. This biogeographical pattern is seen in several lichens that occur in coastal forests of the Maritimes and Maine and also in the northern and southern Appalachian Mountains (see Clayden 2010 and Allen and Lendemer 2015 for examples).

Elsewhere in the world, H. squamulosa consistently occurs in areas with a pronounced geographic relief or in relatively close proximity to the ocean, or frequently both (CNALH 2020). Data from weather stations from New Brunswick and Nova Scotia, and from many occurrences around the world spanning four continents, suggest a minimum annual precipitation of 1,000 mm is required (Anderson et al. 2011; PRISM Climate Group 2013; IPCC 2014; Climate-data.org 2021).

The New Brunswick and Nova Scotia occurrences, along with those in Maine and New England, survive in the coldest climate for H. squamulosa in the world (see Global Distribution). Mean annual temperatures range from 4°C to 8°C in this region, compared to above 8°C in other temperate regions where H. squamulosa occurs and well above 10°C elsewhere (Government of Canada 2021a,b; NOAA 2021a,b; Tutiempo.net 2021; WorldClimate.com 2021). This suggests that colder temperatures in suitable habitats further north may inhibit a broader distribution range for this lichen in Canada. Cold air temperatures and intense ultra-violet radiation levels are harmful to some lichen species. The more moderate temperature, the relatively high number of days with cloud cover, and the high relative humidity enable H. squamulosa to thrive in Nova Scotia and coastal parts of New Brunswick but not in continental New Brunswick and much of eastern Canada.

For about three quarters of occurrences, soils are well-drained, while the rest of the occurrences are influenced by poorly drained soils. All are in areas of lower-acidity bedrock or glacial till, or both. In both soil drainage types, based on soil profiles under uprooted trees, and on indicator vascular plant species at several occurrences, there is significant nutrient enrichment. A tree bark’s physical and chemical properties, and in turn a host tree’s suitability for H. squamulosa colonization, are affected by soil properties (Gustafsson and Eriksson 1995). Predictive soil type GIS data in Nova Scotia suggest that H. squamulosa occurrences in the province occur on moderate to rich, fresh to moist (occasionally wet) soils (NSDNR 2010; NSDLF 2020). Soil richness appears to be particularly important. In the southern half of Nova Scotia, where most Canadian occurrences of H. squamulosa are found, there is an abundance of poor, acidic soils. Correspondingly, the availability of habitats with a combination of old undisturbed forest and richer soils is limited.

When observed growing in wet or lowland sites, occurrences are often close to a slope and near running water, suggesting that inputs of minerotrophic flows produce soil conditions more akin to upland H. squamulosa occurrences. Nearly 72% of observations with aspect data (n = 89) were on slopes, with a strong association with northern aspects. However, the dozens of north-facing occurrences in the Cape Split area produce a strong bias in this analysis. Outside of Cape Split, there is no clear preference for slope position or aspect.

All available data indicates that H. squamulosa has a preference for mature to old hardwoods or for old mixedwood forests. In other words, these are forests with high temporal continuity (McMullin and Wiersma 2019). No occurrences of H. squamulosa were found in habitats with obvious signs of past forest harvesting. All 82 observations with forest maturity information describe H. squamulosa forest habitat as mature climax, old, or old-growth forest (sensu NSDNR 2012). This suggests a minimum dominant or co-dominant tree age of at least 80 years, as well as long-term forest type and cover continuity. Heterodermia squamulosa appears to be relatively sensitive to open sunlit conditions; no occurrences have been found in places with < 50% crown closure.

Yellow Birch, Sugar Maple, Red Maple, White Ash, and Eastern White Cedar (Thuja occidentalis) are the only known host tree species in Canada. Sugar Maple and Yellow Birch are the predominant host tree species in upland sites, while Red Maple, Yellow Birch, and White Ash provide host tree microhabitats for H. squamulosa in wetland and wetland-edge sites. The lone occurrence on Eastern White Cedar was clear-cut in 2006; however, cedar trees have been recorded as hosts in New England (CNALH 2020) and remain as potential H. squamulosa hosts in New Brunswick or Nova Scotia. However, recent searches of this host tree in these provinces have so far been unsuccessful. Several thalli in Nova Scotia were noted as growing on bryophytes on bark, instead of directly on bark. Only three of nine occurrences with aspect data were found on the southeast, south, southwest, or west sides of host trees, possibly suggesting an aversion to high light or heat loading leading to desiccation stress. Most thalli are located between 1 and 2 m above ground, with the lowest and highest thalli at 0.1 and 3.5 m above ground, respectively. Only three host trees were visibly leaning, suggesting that this characteristic is not as important to H. squamulosa as it is for other rare lichens in eastern Canada (COSEWIC 2019).

Heterodermia squamulosa is strongly associated with several other lichen species with an Appalachian biogeographical affinity (Hinds and Hinds 2007) and is a strong indicator of mature to old forest conditions (see Interspecific Interactions). Only two occurrences in the United States (both collected in West Virginia by J.C. Lendemer) of over 500 occurrences had associated lichen taxa that were similar to those found in Canada and are listed in Table 2 (CNALH 2020).

In the eastern United States, H. squamulosa is found in hardwood forests, especially on mossy tree bases (Brodo et al. 2001; Lendemer 2009). With respect to host species, data are available from the specimen labels of over 500 collections of H. squamulosa (CNALH 2020). These show that in the United States, the most common host trees are oak (Quercus spp.) and American Beech (Fagus grandifolia). Several occurrences were noted as growing on bryophytes, both on bark and on the ground. Rock is also an occasional substratum in eastern United States and in other countries (Moberg 2011; CNALH 2020), but H. squamulosa has not been found on rock in Canada.

Several habitat requirements are difficult to map because of a lack of high-precision geographic data. This limits the ability to accurately assess habitat trends and population abundance (NSDNR 2016; NBDNRED 2017). More accurate data are needed, over several time periods, to capture the requirement of this species for temporally continuous connected habitat. This need is a consequence of the very limited dispersal mechanism inH. squamulosa (see Dispersal and Migration). In this report, the use of coarse-scale data and a predictive GIS model likely resulted in an over-estimate of the amount of present-day suitable habitat, and in turn an over-estimate of the population abundance (see Population Sizes and Trends).

Based on habitat preferences and human alteration of habitat, the amount of remaining habitat for H. squamulosa in New Brunswick and Nova Scotia is very small. An analysis between 2008 and 2012 of permanent sample plots indicates that forests over 80 years old represent approximately 16% of forests in Nova Scotia (NSDNR 2017). In addition, approximately 38% of forest cover in Nova Scotia is represented by hardwoods or mixedwoods (<25% softwood composition, representing approximately 1.6 out of 4.2 million ha). Overall, only 6% (16% of 38%) of the province’s forests are of a suitable age and composition for colonization by H. squamulosa (NSDLF 2019). A reasonable estimate of maximum potential suitable habitat is that just 4% has enough temporal and geographic continuity to sustain H. squamulosa (see Threats – Logging and Wood Harvesting).

Habitat trends

Historically, old hardwood and mixedwood forests were much more frequent in New Brunswick and Nova Scotia; prior to European contact with Indigenous peoples, they may have covered about 50% of the Maritime Provinces (see Loo and Ives 2003; Mosseler et al. 2003; Stewart et al. 2003). In this region, the amount of mature to old forests has significantly declined since the late 18th century. The loss of old forests was the result of clearing for agriculture, land development, forest fires, and tree harvesting. Agricultural clearing peaked in the 1890s, when approximately 15% of the Nova Scotian land base was used for farming (MacKinnon 1991). This figure should be treated as a minimum for total area cleared for agriculture in the province, because other previously cleared areas had already been abandoned and regrown into shrubby or forested lands. The amount of land clearing in New Brunswick is likely similar, based on the two provinces’ comparable socio-economic history and currently active farmland. Land development, including residential, commercial, transportation, and other permanent or semi-permanent forest clearing activities, currently accounts for over 3% of the landscape in both provinces (Gorelick et al. 2017; NSDNR 2017). Forest fires, mostly anthropogenic (naturally-occurring fires are exceedingly rare), historically burned large swaths of both provinces; however, this disturbance was poorly defined spatially, and specific impacts to H. squamulosa habitat are largely unknown (Wein and Moore 1979). If not burned, the forests have been harvested, often through clear-cutting, which continues to be the most common forestry practice in both provinces. About 15% of Nova Scotia’s forests were clear-cut between 1990 and 2007 (Cheng et al. 2009), an annual rate of 0.88%, a trend that appears to have continued since 2007, based on annual satellite imagery (Gorelick et al. 2017). A slight decline in overall annual harvesting occurred late in the 2000s and into the 2010s due to the economic recession and to the associated idling or shutdown of forestry mills (Lahey 2018a). Clearcutting was the method of forest harvesting for approximately 65% and 89% of harvests on public land and private land, respectively, in Nova Scotia in 2016. In New Brunswick, clearcutting has represented 80% or more of the total provincial harvest from the late 1990s to the early 2010s. The harvest levels were, and continue to be, similar to those in Nova Scotia (Auditor General of New Brunswick 2015; Gorelick et al. 2017). Harvesting of shade-tolerant hardwood forests in New Brunswick has increased sharply over the past few decades (Clayden 2014).

In New Brunswick, there are swaths of public lands in central and southern parts of the province (including lands immediately adjacent to known H. squamulosaoccurrences) (J.D. Irving Limited 2014). Mature forests comprise 37% of the forested land base, with approximately 35% of that being mixedwood and hardwood; this represents approximately 13% of suitable habitat availability, although only a small amount is climatically suitable. The New Brunswick threshold for “mature” status is 65 years old for Red Maple and 75 years old for shade-tolerant hardwoods, including Sugar Maple and Yellow Birch (J.D. Irving Limited 2014). Given this, and the fact that only the southern fifth of New Brunswick seems to be climatically suitable (i.e., within approximately 50 km of the ocean), a reasonable estimate of the maximum potential suitable habitat in that province is approximately 3%. Compared with pre-colonization times, mature to old forests have declined significantly (Loo and Ives 2003; Stewart et al. 2003).

In summary, the majority of old forests in Nova Scotia and New Brunswick were lost during initial colonial activities by land clearing and forestry. Even though the amount of old forest loss is smaller today, it is still significant and limits the amount of available suitable host trees for H. squamulosa.

Acid rain has resulted in widespread soil acidification in New Brunswick and Nova Scotia, which can lead to a change in forest vigour and composition. For example, a reduced growth rate of Sugar Maple on acid or non-calcareous soils has been reported from Quebec and New England since 1960. This can be attributed, at least partially, to soil acidification and acid deposition levels (Ouimet et al. 2001; Schaberg et al. 2001; Duchesne et al. 2002; Schaberg et al. 2006). Reversal of the negative impacts of acid rain on soils has only recently begun in some parts of northeastern North America (Lawrence et al. 2015). Although H. squamulosa is usually found in nutrient-rich sites (sensu NSDNR 2010), the southern New Brunswick and southern Nova Scotia occurrences predominantly involve trees growing on non-calcareous soils that would buffer impacts of acid rain less well compared with occurrences in Vermont (see Threats: Air pollution). In Atlantic Canada, acid rain has likely caused and will continue to cause reduced growth and potential mortality in Sugar Maple trees, a regionally important host tree for H. squamulosa, thereby reducing the amount of available substrate for colonization.

In Atlantic Canada, there have been significant declines in mature American Beech trees due to Beech Bark Disease. While this is not currently a significant threat, and no Canadian occurrences of H. squamulosa are known from this host tree, it is a common host in the USA. Hence, this disease may well have reduced the amount of suitable habitat for H. squamulosa in New Brunswick and Nova Scotia in the past. Recently, the number of healthy American Beech trees has increased owing to the spread of disease-resistant individuals (Houston 1983; Stephanson and Coe 2017; AC CDC 2020). However, healthy trees are relatively rare in the Atlantic Provinces of Canada, and there is a lack of forest harvesting practices aimed at preserving them.

Biology

Life cycle and reproduction

Heterodermia squamulosa’s primary means of reproduction is by vegetative lobules (phyllidia). Apothecia are known from South Korea (Wang et al. 2008) and from two specimens in North America (one in Digby County, Nova Scotia) (CNALH 2020), but there is no information on the presence, viability, and dispersal of spores from the apothecia in this species (CNALH 2020). With only one fertile specimen (see photo front page) out of hundreds of known thalli in Canada, the apothecia do not represent a common or effective method for dispersal of H. squamulosa in this region.

Lobules contain both the green alga Trebouxia as the photobiont and the mycobiont species. Lobules can be anchored (established) within a year of reaching suitable habitat. The pattern of growth changes as the new thallus expands (Seminara et al. 2018); growth zones differentiate, and lobes become evident (Armstrong and Bradwell 2011). In the Canadian population, several thalli measuring just over 1 cm² were observed to be starting to form lobules. The largest thallus was approximately 300 cm² (with a radius of 100 mm). The largest group of thalli on one tree measured roughly 3,500 cm² and was found at Shingle Lake, Lunenburg County (Table 3).

Determining the average age of lobule-dispersing individuals is imprecise because of the lack of long-term monitoring and the challenge of delineating individual thalli. However, lichenometric methods, such as extrapolating thallus age by dividing mean thallus diameter by mean growth rate, have been used to make age estimates for other at-risk lichens. Published data on other members of the Physciaceae from temperate regions helps to provide estimates of growth rates and age ranges for H. squamulosa. The annual growth range for eight Physciaceae species (including H. speciosa) across 10 studies in temperate regions was 1.38 to 1.89 mm/yr (Hayward and Grace 1999; Armstrong and Bradwell 2011). The estimated average width of 20 lobule-bearing individual thalli from photographs taken at nine sites from the 2019 surveys in Nova Scotia was 26 mm, ranging from 10 to 100 mm. Only photographs of thalli that were clearly a single entity were used, because thalli in this species can split and/or merge, which makes age estimation more difficult. Using single thalli, the minimum and maximum estimated ages for H. squamulosa thalli in Nova Scotia that are old enough to produce reproductive lobules was between 5 years for a young thallus and 72 years for a large, very old thallus. The estimated mean age of lobule-bearing H. squamulosa thalli in Nova Scotia was estimated to range from 14 to 19 years. Generation times for old forest lichens based in juvenile development have given results ranging from 9 to 22 years (Larsson and Gauslaa 2011).

The climate for the Canadian population of H. squamulosa is the coldest in the world. Both lower temperatures and lower light levels tend to result in lower growth rates in lichens (Palmqvist and Sundberg 2001). As a result of the expected slower growth rate, the age of 19 years, rather than 14, is used as the generation time for H. squamulosa in this report, giving a three-generation time of 57 years.

In Nova Scotia, the thallus that has been re-located after the longest interval is one at the Lily Lake occurrence. This was documented again 14 years after it was first recorded. The lichen was located again based on a description of the host tree, its position, and the habitat described by the original observer who documented the discovery in 2005 (T. Neily pers. comm. 2019). However, it is not known if the original thallus has changed (e.g., split into several thalli) or if a new thallus has grown on the tree from vegetative propagules released by the original thallus.

Physiology and adaptability

Some thalli in the Canadian population of H. squamulosa exhibit a very high tolerance of deep shade. For example, many thalli in the Cape Split occurrence were found on the north side of trees on steep, north-facing slopes. The north side of the host trees, under a dense forest canopy from June to October, seldom receives direct sunlight. This apparent ability to metabolize in cool, dark conditions may be attributable to the presence of atranorin in its chemistry (C. Deduke pers. comm. 2022). This, combined with the fact that its global distribution does not reach further north than New Brunswick and Nova Scotia, suggests that H. squamulosa needs a moderate maritime climate in order to persist in a region. The symbiont of H. squamulosa is the alga Trebouxia, which is unable to fix atmospheric nitrogen, which may partially explain the preference of this lichen for colonizing trees that grow on nutrient-rich soils that provide throughfall that is richer in nutrients (sensu NSDNR 2010; see Habitat – Habitat Requirements). Some species of Trebouxia are non-lichenized and occur independently in the wild (Bubrick et al. 1984; Mukhtar and Galun 1994). It is not known which species of Trebouxia is required by the fungal component of H. squamulose, but recent research has shown that it likely belongs to the I, A, or C clade of Trebouxia (Kosecka et al. 2022). Many lichens have a basidiomycete fungus as a third partner in the symbiosis (Spribille et al. 2016), but Lendemer et al. (2019) found no cystobasidiomycete yeast in two H. squamulosa specimens.

Dispersal and migration

Heterodermia squamulosa reproduces asexually by means of lobules (phyllidia) that are dispersed by wind, animals, or flowing water. Older thalli (generally > 5 cm²) will often exhibit numerous lobules. Occasionally, thalli have a frayed appearance after many of the lobules have been dispersed, exposing the medulla. Dead sections of a large H. squamulosa thallus at Shingle Lake had almost no remaining lobules.

Heterodermia squamulosa lobules are larger and heavier than other asexual propagules, such as soredia and isidia, that are produced by many lichens. As a result, lobules are not easily dispersed by wind and are likely to travel shorter distances than isidia or soredia (Scheidegger and Werth 2009). However, they may have a higher success rate in terms of colonization at the forest stand level (Hedenås and Ericson 2008; Fedrowitz et al. 2012; see COSEWIC 2019). This notion appears to be supported at several occurrences in Nova Scotia (e.g., Cape Split, Churchills Lake, Van Tassel Lake) where many trees within one contiguous area of suitable habitat are colonized by H. squamulosa. In Canada, most occurrences are found 1–3 m above the ground. Assuming a height of 5 m, lobules falling off a thallus would spend about 1 second in freefall. Maximum wind speeds observed in this region are typically ~100 km/h, which could carry lobules up to 28 m. Sloping ground or a slower freefall speed as a result of the small lobule size and the relatively high surface-to-weight ratio could extend the maximum dispersal distance to an estimated 50 m. Although this is only a rough estimate, it provides a picture of the physical constraints placed on this species’ with respect to its ability to disperse across the landscape.

Animals probably play an important role in both intra- and inter-stand dispersal (see COSEWIC 2020). Propagules carried by mammals, such as Northern Flying Squirrel (Glaucomys sabrinus), Southern Flying Squirrel (G. Volans) and Red Squirrel (Tamiasciurus hudsonicus), could be carried several hundred meters, while those carried by birds could travel longer distances. Bark-gleaning bird species, such as Brown Creeper (Certhia americana) and woodpeckers (Family Picidae), are more likely to be in contact with H. squamulosa (and therefore to pick up its lobules) than other bird species. Typically, resident species do not migrate large distances. A recent review of the literature on bark-gleaning bird species suggests that the home ranges of most Nova Scotia taxa are only a few ha in size, and the greatest travel distances range from 1 to 10 km (COSEWIC 2020). In conclusion, H. squamulosa probably undergoes regular intra-stand dispersal, but longer inter-stand dispersal events are likely rare. As a result, there is little chance of this species dispersing easily in the current patchwork landscape of Atlantic Canada. It is thus not surprising that in 25 of 30 occurrences, the lichen is found on fewer than five host trees, and most occurrences are currently surrounded by unsuitable habitat (see Habitat).

Interspecific interactions

Grazing by gastropods may limit growth and early development in macrolichens (Asplund and Gauslaa 2008) and may be contributing to declines in Boreal Felt Lichen (Erioderma pedicellatum) and Vole Ears (E. mollissimum) (Cameron 2009). No evidence of grazing has been documented on H. squamulosa, but it may take place, as invertebrate grazing occurs on a broad range of lichens (Seyd and Seaward 1984; Baur et al. 1995; Pöykkö et al. 2005). Heterodermia squamulosa is found to be associated with a group of lichens that are also strong indicators of mature to old forest conditions (Table 2).

Population sizes and trends

Sampling effort and methods

The fieldwork goals for this report were: (1) to visit as many known sites for H. squamulosa as possible to verify the current status (e.g., presence, number of thalli, number and species of host trees, site characteristics); (2) to document additional subpopulations by visiting as many high-probability sites as possible, within time constraints; and (3) to photograph and collect specimens where appropriate. For this report, each thallus found was counted as a “mature individual” according to IUCN (2019) guidelines, as fewer than 1% of thalli had no lobules. The capability of small, immature or poor specimens to reproduce successfully is likely very low. The IUCN’s definition mentions “individuals known […] to be capable of reproduction”, and this is open to further interpretation. In summary, the definition used in this report could result in an overestimation of reproductive capacity of H. squamulosa in Canada and should be considered when interpreting the following sections.

Most field surveys for known occurrences took place during the autumn of 2019. Surveys focused on the 16 occurrences that had not been visited since 2017. Eleven other occurrences with data from 2018 onward or having been found in 2020 were considered recent enough that no further visit was needed. Photos and voucher specimens were also collected, when appropriate. In New Brunswick, of the seven occurrences, one was presumed no longer extant due to clearcutting observed on satellite imagery, and a second was presumed no longer extant after searching by experts. Two others were not searched because of remoteness or geographic uncertainty, and another because the occurrence was only reported after field verification had been completed. In Nova Scotia, of the 24 occurrences, 13 were visited in 2019, and 10 had data from 2018 onward or were found in 2020 (Table 3). The Lac de L’École occurrence was not visited because the position of the original site was uncertain (~2300 m radius around the coordinates). Surveys of known occurrences in 2019 consisted of one to four surveyors meandering through a site until H. squamulosa was relocated, or not. Surveyors looked at all suitable tree hosts within approximately 50 m of the coordinates provided by the original record of the occurrence.

Abundance

The total number of current and historical occurrences in Canada is 31, with seven in New Brunswick and 24 in Nova Scotia (Table 3). This table includes data on the date of surveys, number of thalli and colonized trees and whether the lichen was missing from some previously known sites at an occurrence; listed in the table as “Extant but partial loss of occurrence”.

Total Individuals^* trees = 145
Total Individuals^* Thalli = 450+
Year discovered 1980-2020

*Data reflects most numbers available the time of writing this report (2020).

The numbers of host trees and thalli were estimated using surveys. Most included thallus counts on one or a cluster of host trees separated by a minimum of 10 m. Host tree data were consistently recorded by the lichen surveyors, and the total number of trees was 145. Seven host trees were in New Brunswick, while 138 were in Nova Scotia. The average number of host trees per occurrence was 4.8 across the entire population or 2.2 if the Cape Split occurrence is not included. The occurrence at Cape Split (Scots Bay subpopulation) comprises approximately 50% of all the known thalli on about 50% of the colonized host trees. While more than 73 new thalli and 31 new host trees were discovered in extensive surveys done in 2019 and 2020, the total known population is only about 500.

Estimating the total possible number of thalli present in the past is difficult, because thallus numbers were not recorded in a consistent way from the time that the species was first found in the Maritimes in 1980. The number of thalli that have been recorded is 421, but the number of host trees for which thallus counts were not made is 31. Dividing the number of total thalli (450, see Table 3) by the number of host trees (145) produces an average 3.1 thalli per tree. The 31 host trees without thallus records can thus be estimated to host 65 additional thalli. The one host tree with 74 thalli in Shingle Lake skews the thalli-per-tree average overall, as do the occurrences in the Scots Bay subpopulation at Cape Split in Nova Scotia. The latter has the largest recorded number of thalli (247 thalli on 79 host trees, out of a total of 450 thalli). The maximum number of thalli at known occurrences is estimated at 450 to 515, with 25 to 29 thalli located in New Brunswick and 425 to 486 thalli located in Nova Scotia. Even taking into account the >73 new thalli and 31 new host trees discovered in recent surveys (2019/2020), and the estimates of the small amount of suitable undisturbed habitat (c. 4%) (see Habitat Trends) for H. squamulosa, it is estimated that the total population of mature individuals of this lichen in Canada is < 1,000.

A species distribution model was also used to help estimate the total number of host trees for H. squamulose, following methods employed for White-rimmed Shingle Lichen (Fuscopannaria leucosticta) (Appendix 1). First, Predicted Abundance (PA) was calculated by multiplying the Probability of Occurrence (PO) of H. squamulosa (from the Species Distribution Model predictive surface) by the Known mean Abundance (KA; the number of known host trees within each 50 m² area or the number of occupied 50 m cells) within areas of the province with sufficient survey effort for H. squamulosa. Correction factors, based on observed versus predicted occupancy, were then applied to PA estimates using classification tree analysis (Setchell and Haughian 2021) to correct for the approximate proportion of searched sites that contained H. squamulosa. Based on this model, the calculated estimates for the number of thalli and the number of host trees were 756 and 937, respectively. This is likely an overestimate for Nova Scotia, because the habitat parameters used in the model are likely broader than what the species actually tolerates or needs. Nevertheless, because the estimates are within the same order of magnitude as the observed population size and because the model does not account for population contributions from New Brunswick (which includes 4.2% of known host trees for Canada), these numbers may serve as a conservative high-end estimate for the Atlantic Canadian population. Despite low survey rates, New Brunswick likely has fewer occurrences than Nova Scotia, given the rarity of this species in adjacent New England (where survey effort is similar or higher). The colder climate and more varied topography may provide Nova Scotia more opportunities for wetland occurrences. It should be noted that the model included all of Nova Scotia. More than half of Nova Scotia has no H. squamulosa occurrences. This also seems likely for the part of New Brunswick that was not included in the model and supports the overall abundance estimate provided by the model for Nova Scotia and New Brunswick combined.

Fluctuations and trends

Population trends for H. squamulosa are difficult to assess in Canada, because only nine occurrences (Table 4) have been enumerated more than once. For trend assessment, only those occurrences with either reliable host tree or thallus counts or estimates from at least two observation years were used. Among nine occurrences that qualified for the analysis (two in New Brunswick, seven in Nova Scotia), seven showed declines in host trees in 2019, while two others showed no change (Table 4). Of the occurrences considered to be no longer extant, three (Grand Bay-Westfield, Hectanooga, and Spider Lake) have been subject to clear-cut harvesting (as defined in Natural Resources Canada 2020). Two other sites (Upper LaHave) may have been subjected to over-collection before the rarity of the species in the province became known. At two sites (Welsford and McGahey Brook), suitable habitat appeared to persist, and the reason for the disappearance of H. squamulosa was not clear. The Welsford site is on Canadian Forces Base (CFB) Gagetown lands (AMEC 2011), and the lichen could not be found, even though the trees are unlikely to have been cut. However, other species in this region, such as Erioderma pedicellatum and E. mollissimum, are known or suspected to be in decline as a result of air pollution and nearby forest alteration (COSEWIC 2009, 2014, 2015, 2020).

^* 1+ indicates a minimum of 1 thallus (the data did not provide a finer resolution).

Using data from observation sites with two reference years, the annual decline rate for the number of host trees for H. squamulosa was 4.5%. Based on limited available data from the nine observation sites (summarized in Table 4 and Box 4 of the Technical Summary), a loss of 33% of host trees to logging and 22% of host trees to unknown causes can be inferred from the average 12.25-year span between first and second monitoring visits (excluding Spider Lake, for which the original survey year is unknown).

The predicted future yearly decline rate of H. squamulosais 3.6% or 18% over 5 years and is based on past decline rate in host trees, with weighted average adjustments on protected land, i.e., where forest harvesting should not occur (see Habitat Protection and Ownership). This estimated annual decline rate of colonized host trees (See Appendix 1) is used to estimate a decline in population of H. squamulosa as exceeding 50% over a three-generation time period. This is reported in box 5 and 6 of the Technical Summary. Declines are largely caused by continuing threats (see Habitat Trends; see Threats), justifying their use in estimating future loss. Non-protected host trees (68.1%) are expected to decline by the full 4.5% rate each year, while protected host trees (31.9%) are expected to decline by 1.5% (see Habitat Trends).

Fourteen of the total 31 occurrences were documented as new for the Canadian population since 2017 (Table 3). The new occurrences have likely been in existence but not documented for at least a decade, judging from the size of thalli and the generation time. H. squamulosa was first found in New Brunswick in 1980 and in Nova Scotia in 1987. As a result of the decline in old forest habitat in both provinces (see Population Sizes and Trends; see Threats), an overall decline in the number of mature individuals is likely.

In New England, USA, where the nearest non-Canadian population of H. squamulosa occurs, there are insufficient data to assess fluctuations and trends. In 2007 there were four known occurrences in Maine (Hinds and Hinds 2007). A fifth record from this state is from Roque Island, a private island with a very rich lichen flora that includes three species of Heterodermia. The mature forest there has only been selectively cut on a very limited scale (Seaward et al. 2017), A sixth record for New England is from New Hampshire (Clyne 246-16 CUP; Cleavitt 2020; Hinds 2020).

Rescue effect

The likelihood for mitigation of declines in the Canadian population ofH. squamulosa or rescue from US populations of this lichen is very low. This is a result of the dispersal limitation of the lichen and the large distance between US subpopulations and suitable Canadian habitat. The nearest non-Canadian occurrence of H. squamulosa is over 100 km away, in Maine (see Wildlife Species Description and Significance; see Population Spatial Structure and Variability). A total of six occurrences are known in New England. Beyond this is a gap of approximately 500 km to Pennsylvania, where the species is also present. It becomes more abundant southwest along the Appalachian Mountains (Figure 1).

Threats and limiting factors

Threats

The Threats Calculator was used in 2021 to assess the threats to H. squamulosa in Canada, and the overall impact was high (Appendix 2). The various threats to this lichen are discussed below. The threats are organized and evaluated according to the unified threats classification system (IUCN and CMP 2017) of the International Union for the Conservation of Nature - Conservation Measures Partnership (IUCN-CMP). The threats that directly and negatively affect the H. squamulosa population are listed below from highest to lowest calculated impact.

Road building (IUCN Threat 4.1 Roads and railroads) impact: medium

Road building results in the clearing of forest habitat, opening up of the canopy, modification of local hydrology and alteration of moisture and air quality conditions in adjacent forest ecosystems. Heterodermia squamulosa is sensitive to open sunlit conditions,and no occurrences have been found in places with < 50% crown closure. Thus, road construction results in a loss of the species from the adjacent forest. The threat from road construction includes both those built for forestry, e.g., the Spider Lake occurrence, and those built for cottage development, such as that found near the Hirtle Lake occurrence. Future road building poses a threat to H. squamulose, as 68.1% of host trees are not currently within protected areas and roads could therefore be constructed next to the sites.

Logging and wood harvesting (IUCN Threat 5.3 Logging and wood harvesting) impact medium

As mentioned above, H. squamulosa is sensitive to open sunlit conditions, as no occurrences have been found in places with < 50% crown closure. Consequently, logging results in the definitive loss of trees with thalli, but also results in a decrease in habitat quality on trees with thalli in proximity to harvested areas. Logging resulted in the partial loss of the Spider Lake occurrence in 2016 or 2017 and the loss of the Grand Bay-Westfield occurrence in 2014 or 2015.

While some H. squamulosa occurrences are found in operationally challenging terrain, such as steep slopes or wetlands, most sites where the lichen was observed could be harvested in the future. As evidence, 12 occurrences were found within 100 m of clearcutting (as defined by Natural Resources Canada 2020) that has occurred between 1984 and 2018, when satellite imagery became available for GIS analysis (Gorelick et al. 2017). About 15% of Nova Scotia’s forests were clear-cut between 1990 and 2007 (Cheng et al. 2009), for an annual rate of 0.88%, a trend that appears to have continued since 2007 based on annual satellite imagery (Gorelick et al. 2017).

Heterodermia squamulosa relies on very old forests. No occurrence was found in habitats that had visible signs of past machine forest harvesting, such as tree stumps or skidder trails. All forests where it is found are described as mature climax, old, or old-growth forest (sensu NSDNR 2012). This suggests a minimum dominant or co-dominant tree age of at least 80 years as well as long-term forest type and cover continuity. The temporal continuity requirements of this species suggest that other occurrences were lost in the past, given the dominance of clearcutting as a forestry practice in the Maritimes (Johnson 1986; Gorelick et al. 2017; Lahey 2018a, b; Global Forest Watch 2020). Most forests of New Brunswick and Nova Scotia have been logged in the past and continue to be included as part of the timber landbase.

The threat from logging in Nova Scotia could be reduced by a commitment by the provincial government, as outlined in the Lahey Report (Lahey 2018a, b), to reduce clearcutting from the present-day level of 65% to between 20% and 25% on Crown land. However, this has not yet been implemented and only applies to Crown land. Only five host trees from one occurrence of H. squamulosa have been found on Crown land, and protection for them is currently pending (NSE 2020). Another 93 host trees from 17 occurrences are unprotected as they are on private land and may be subject to future logging. At least in the short term, the proposed ban on clearcutting on Crown land will probably result in an increase in clearcutting on private land. While the Nova Scotia Endangered Species Act fully applies on both private and Crown land, on private lands the onus is on the private landowner to ensure that prohibitions under the Act for threatened or endangered species are not breached.

Acid rain (IUCN Threat 9.5 Air-borne pollutants) impact medium-low

An adverse change in air quality and precipitation pH, and resulting changes of bark pH, soil pH and nutrient availability, can both directly affect lichen growth and impact habitat quantity and quality through their effects on forest composition and vigour, and on physical and chemical properties of trees, including the texture and moisture-retaining ability of bark (OMNR 2004; see COSEWIC 2020). Heterodermia squamulosa is known to occur in habitats with nutrient-enriched soils, which may have buffered these effects to some extent. However, nutrient-enriched sites are still being impacted by acid precipitation (Nieboer et al. 1984) through the stunting or killing of suitable host trees. Acid rain pollution diminished significantly in the late 1980s and 1990s. Some effects may persist, but sites may be slowly recovering.

Land development (IUCN Threat 1.1 Residential and commercial development) impact low

Residential development results in the clearing of forest habitat and modification of local hydrology, humidity and air-quality conditions in adjacent forest ecosystems. The area within 200 and 500 m of the Hirtle Lake occurrence has experienced a significant increase in dwellings since 1978 (Gorelick et al. 2017), accompanied by road building and land clearing. Much of the development has occurred since 2016. The Hirtle Lake occurrence is found in an area with already-subdivided plots, and upwards of 30 dwellings are within 500 m of the occurrence. The Cape Split occurrence has also experienced ~0.1 hectares of forest clearing for dwellings and viewscapes for these dwellings. The latter clearing resulted in the removal of trees in habitat (steep slope-tolerant hardwood forest) in which H. squamulosa is prevalent, and H. squamulosa was found on both sides of the clearing. Although it is impossible to know with certainty that host trees were removed, based on occurrence data and presence of suitable habitat in adjacent uncut forests, host tree loss is likely. No other occurrence appears to be threatened by residential development at this time.

Fire (IUCN Threat 7.1 Fire and fire suppression) impact low

An increase in fires is expected as a result of the recent and predicted increase in the length and severity of summer droughts (see Climate Change). Forest fire ignitions are mostly anthropogenic in origin and are expected to continue to occur. The hardwood component of suitable H. squamulosa habitat does provide a protective buffer against extensive fire damage, which generally points to a low level of impact.

Invasive species (IUCN Threat 8.1 Invasive non-native/alien species/diseases) impact low

Several invasive species are known to kill or stunt the growth of hardwood trees in the Maritimes (Belliveau and Mersey Tobeatic Research Institute 2012). The Emerald Ash Borer (Agrilus planipennis), confirmed in New Brunswick and Nova Scotia in 2018 (CFIA 2020), is known to kill most species of ash tree in infested areas (COSEWIC 2018). Of 144 total host trees for H. squamulosa in Canada, eight are White Ash trees (which support a total of 25+ thalli), and nine others are in forested ecosystems dominated or co-dominated by White Ash, all of which are in southwestern Nova Scotia. The shortest distance between a present Emerald Ash Borer infection and an occurrence of H. squamulosa in White Ash habitat is approximately 95 km. This insect appears to be capable of jumping hundreds of kilometers in range in just a few years (CFIA 2020), which suggests that White Ash trees and other host tree species within White Ash forests may be negatively affected within a single H. squamulosa generation. Some thalli of this lichen may survive on other trees upon the death of White Ash trees in an occupied forest; thus the severity of this threat is considered serious rather than extreme.

Climate change (IUCN Threat 11 Climate change and severe weather) impact: unknown

A high level of uncertainty exists regarding climate change in Nova Scotia with respect to fog, precipitation and wind (Lemmen 2016; McClearn 2018). Higher temperatures, with more frequent extreme temperature events and high precipitation events as well as earlier spring thaws, may have already stressed H. squamulosa. Direct impacts may include physical stressors from changes in moisture availability or changes in freeze-thaw cycles, while indirect impacts may include metabolic and other chemical changes within the lichen.

The apparent coastal affinity of Canadian H. squamulosa occurrences suggests that this species requires a relatively moist climate influenced by frequent fog (See Habitat requirements). Declines in fog frequency and duration could potentially negatively impact its ability to thrive in coastal forests. In Nova Scotia, multiple trends point to a reduction in fog frequency (Beauchamp et al. 1998; Mucara et al. 2001). New Brunswick trends are likely similar, although data are not available for the province.

Higher temperatures and drought events will significantly reduce moisture regimes in the region despite the increase in projected precipitation in Atlantic Canada (Vincent et al. 2018). For example, projections for the Annapolis Valley, a region of Nova Scotia roughly in the center of H. squamulosa’s Canadian EOO, expects mean annual temperatures in the 2050s to increase by 2.3°C compared to historical data from the 1980s (Climate Data for Nova Scotia 2021). Annual water deficit (potential actual evapotranspiration) is expected to increase (36 mm to 48.8 mm) in the same time period, despite an increase in precipitation (from 1,351.8 mm to 1,396 mm). In New Brunswick, projected climate change signals are similar to Nova Scotia. In Saint John, a city situated on the Fundy coast within H. squamulosa’s Canadian distribution, mean annual temperatures in the 2050s are projected to increase by between 2.2°C and 3.1°C compared to the historical reference period from 1981 to 2010 (Roy and Houard 2016). Annual precipitation is projected to increase from 6.8% to 7.9% in the same period, but no projections on water deficits have been made. Broadly, drier conditions are projected for all Maritime Canada, although coastal areas may be impacted less than inland regions (Vasseur and Catto 2008). Outside of Canada, H. squamulosa grows in areas where there are higher temperatures and more precipitation, both of which are expected to increase in Atlantic Canada with climate change (Vincent et al. 2018), suggesting that these changes may not affect this species.

An increased frequency and severity of extreme weather events is expected (Vasseur and Catto 2008, Vincent et al. 2018). The latter could result in more windthrow of host trees for H. squamulosa. Additionally, loss to windthrow may be more likely on the older, often taller old host trees required by H. squamulosa in comparison to the younger, shorter, and denser forests that frequently result from past forest harvesting activities. The host trees at the Cape Split occurrence, where the greatest population of the lichen is found, are not only in a very windy area but are also especially vulnerable to uprooting, given that Yellow Birch, the main host species at Cape Split, tends to grow leaning at an angle on the steep slopes. Windthrow losses are also likely to have a greater impact on lichen survival at the 23 occurrences where there are fewer than five host trees.

Changes to the winter freeze-thaw cycle, the timing of frosts, and the frequency of ice storms are possible threats (Vasseur and Catto 2008, Vincent et al. 2018). These could increase damage to host trees. For example, in eastern North America, winter freeze-thaw has been linked to historical dieback of Yellow Birch (Bourque et al. 2005), of which at least 62 are host trees for 92 thalli.

Trail clearing (IUCN Threat 1.3 Tourism and recreation areas) impact: negligible (see Appendix 2 comments.)

Clearing trees for trail building or upgrading can result in the removal or harm of host trees for H. squamulosa and other lichens of conservation concern. Several cut trees were reported in 2020 from the Cape Split Trail (Cape Split Provincial Park), approximately 1 km into the trail from the parking area and within suitable H. squamulosa habitat. It is not known if the removed trees hosted any thalli, but the lichen is very common at this occurrence, with over 200 thalli being recorded.

Utility and service lines (IUCN Threat 4.2 Utility and service lines) impact negligible (see Appendix 2 comments.)

Utility and service lines may be constructed in order to service new residential developments or cottages. Such activities could destroy or alter habitat for H. squamulosa.

Non-lethal harvesting (IUCN Threat 5.2 Gathering terrestrial plants) impact negligible

Some collecting for monitoring of lichen populations has gone on in the past (see Fluctuations and Trends). When necessary, only part of a thallus is now collected for identification or other purposes, so the impact is now negligible.

White-tailed deer herbivory (IUCN Threat 7.3 Other ecosystem modifications) impact uncertain (See Appendix 2 comments.)

White-tailed Deer (Odocoileus virginianus) are known to browse on hardwood seedlings, affecting the recruitment of hardwood trees, and may alter or inhibit the growth of suitable host trees for H. squamulosa. This ungulate is not native to the current Canadian distribution range of H. squamulosa (Nova Scotia and part of New Brunswick) and was introduced to this region just over 100 years ago. As a ruminant, it will consume plants including woody vegetation. Unpublished data from Kejimkujik National Park and National Historic Site, where White-tailed Deer numbers are relatively high, suggest that heavy browsing may result in a lack of recruitment of seedlings into the sapling stage and subsequently into the mature tree stage (Mersey Tobeatic Research Institute 2010). However, as the typical age of trees that host this lichen is > 80 years, lichen abundance will not be greatly affected within the next 57 years (three generations for H. squamulosa) by the increased deer abundance. With respect to lichens, White-tailed Deer can rub snout or hides against the lichen or scrape their antlers in the fall on tree trunks. However, these activities are unlikely to remove significant amounts or H. squamulosa from the trees or lead to an increase in dispersal of the lichen.

Human intrusions and disturbance (IUCN Threat 6.1 Recreational activities) not scored

Several hardwood trees were cut down within 75 m of two occurrences at Bennetts Lake. The trees were cut down to increase visibility in a line of sight between a White-tail Deer hunting blind on the ground and a pile of bait apples. The area where trees were cut down was moderately suitable habitat for H. squamulosa. Several sites (at least Pearl Lake and Van Tassel Lake) are, or have recently been, impacted by All-Terrain Vehicle (ATV) use. ATV trails in suitable habitat, especially in occupied wetland habitat, can alter hydrology and tree health (root damage).

Limiting factors

Habitat specificity

Scaly Fringe Lichen requires mature to old hardwood or mixedwood forest dominated by long-lived, shade-tolerant tree species. Even within surveyed mature to old hardwood or mixedwood forest types, this lichen is limited in local and regional distribution. In short, suitable forest types now represent a very small proportion of forests in Nova Scotia and New Brunswick.

Dispersal

Heterodermia squamulosa is likely dispersal-limited. It can only disperse via its lobules or thallus fragments; longer-distance dispersal events are likely rare, limiting its ability to colonize the small remaining areas of suitable habitat in New Brunswick and Nova Scotia (see Biology – Dispersal and migration).

Northern edge of range

The New Brunswick and Nova Scotia occurrences of H. squamulosa are the northernmost in the world and experience the coldest climate or any global population. The lack of known occurrences further north suggests that its current range in Canada represents its furthest biogeographic reach. It is possible that warming climates will lead to expanded climatic suitability, but the lack of large mature hardwood deciduous trees to the north of current occurrences and limited dispersal ability may impede the northward movement of this rare lichen in Canada.

Number of locations

The number of locations for H. squamulosa in Canada is 29, which is the same number as the number of extant occurrences. This number represents the impact of threats that apply at the local stand scale, such as forestry activities and road construction. There are 31 known occurrences, but two are no longer extant (Table 5).

Protection status and ranks

Legal protection and status

Heterodermia squamulosa is not legally protected in any jurisdiction in which it is known to occur.

Non-legal status and ranks

Globally, NatureServe assigns H. squamulosa a status of G3G5 / Vulnerable to Secure (last reviewed 2000-12-08). In the USA, it is unranked in North Carolina and Pennsylvania. In Canada, H. squamulosa is ranked as N3 / Vulnerable (NatureServe 2021).

At the provincial level, it is ranked S1? / Critically Imperiled in New Brunswick and S3 / Vulnerable in Nova Scotia by the Atlantic Canada Conservation Data Centre (in collaboration with provincial government staff). The species still has an SNR ranking in Quebec, where it does not occur (the only collection was misidentified).

Habitat protection and ownership

Currently, 31.9% of H. squamulosa host trees in New Brunswick and Nova Scotia are in protected areas (as defined by the IUCN), with an additional 3% pending designation to protected status in Nova Scotia, and another 8% that may be protected from tree harvesting by riparian zone regulations (Table 5). In terms of the 29 extant occurrences, 11 (37%) are completely protected from development activities. Four of these protected occurrences, encompassing six host trees, are in Fundy National Park, New Brunswick. The former Welsford occurrence in New Brunswick is on CFB Gagetown lands (AMEC 2011), and so the trees are unlikely to be cut. Eighteen (60%) of the occurrences are not protected. One, Cape Split, is protected in part, as the land ownership is split between a provincial park and private ownership. Most of the land protection in New Brunswick and Nova Scotia has occurred in the last 25 years. This means for H. squamulosa, with its three-generation time frame, that most of the protected areas established to date have a disproportionately high amount of unsuitable habitat for this species and have poor soils. This is, in part, due to the fact that protection has been of lands that are mainly public. In many cases, these lands remained as public land because they were never claimed by settlers that sought areas with fertile soils for subsistence farming.

Total number host trees = 145
Percent of host trees (Protected) = 32%
Percent of host trees (Not Protected)= 68%

Acknowledgements

Much of the fieldwork and report writing was supported by Acadia University’s E.C. Smith Herbarium and K.C. Irving Environmental Science Centre. The report writer thanks the following individuals for their assistance with this report: Frances Anderson (data sharing and volunteer fieldwork), Colin Chapman-Lam (fieldwork, report writing and reviewing), James Churchill (fieldwork, data sharing, habitat suitability modelling, and EOO/IAO mapping), Stephen Clayden (volunteer fieldwork), Sean Haughian (habitat suitability modelling and draft reviewing), Katie King (volunteer fieldwork), Tom Neily (data sharing), David Richardson (report), Charity Robicheau (fieldwork and habitat suitability modelling), Cole Vail (volunteer report research), and Neil Vinson (fieldwork).

Authorities contacted

• Frances Anderson, Research Associate, Nova Scotia Museum, Halifax, Nova Scotia.
• Sean Blaney, Director, Atlantic Canada Conservation Data Centre, Sackville, Nova Scotia.
• Stephen Clayden, Curator and volunteer lichen expert, New Brunswick Museum, Saint John, New Brunswick.
• Sean Haughian, Plant ecologist, Nova Scotia Museum of Natural History, Halifax, Nova Scotia.
• David Richardson, Dean Emeritus, Saint Mary’s University, Halifax, Nova Scotia.
• Mary Sabine, Biologist, Species at Risk and Protected Natural Areas Section, New Brunswick Department of Natural Resources and Energy Development, Fredericton, New Brunswick.
• Mark Seaward, Faculty of Life Sciences, University of Bradford, Bradford BD7 1DP, United Kingdom.

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Biographical summary of report writers

Alain Belliveau is the Irving Biodiversity Collections Manager for the E.C. Smith Herbarium, K.C. Irving Environmental Science Centre for Biodiversity at Acadia University in Wolfville, Nova Scotia. He is responsible for the E.C. Smith Herbarium, the largest collection of vascular plant specimens in Atlantic Canada. He has collected and contributed records for tens of thousands of vascular plant and lichen occurrences in Atlantic Canada. He is a member of several Species Recovery Teams, including the Plants Recovery Team, Black Ash Recovery Team, and the Atlantic Coastal Plain Flora Recovery Team for Nova Scotia. He has written or co-written or is currently in the process of writing or co-writing several COSEWIC and provincial status reports. Prior to employment at Acadia University, Alain received a Master of Resource and Environmental Management and worked for several years as a botanist for both the Atlantic Canada Conservation Data Centre and the Mersey Tobeatic Research Institute.

Collections examined

Lutzoni 840718-L138 QFA: Specimen reviewed and determined to not be Heterodermia squamulosa, thereby removing it as a species known to occur in Quebec. (CNALH 2020).

Appendix 1. Estimation of decline rates for trees and thalli

A Species Distribution Model was used to help estimate the maximum number of occurrences and maximum number of host trees for H. squamulosa following the methods employed by S. Haughian for the White-rimmed Shingle Lichen (COSEWIC 2019). First, the Predicted Abundance (PA) was calculated by multiplying the Probability of Occurrence (PO) of H. squamulosa (from the Species Distribution Model: predictive surface) by the Known Mean Abundance (in this raster model, the cell-size is equal to 50 m;KA; the number of known host trees within each 50 m area or the number of occupied 50 m cells) within areas of the province with sufficient survey effort for H. squamulosa. Correction factors were then applied to PA using classification tree analysis (as in Setchell and Haughian 2021) to correct for the approximate proportion of searched sites that contained H. squamulose. The model did not account for any distribution in New Brunswick (which includes 4.2% of host trees for Canada), but it is thought to be a reasonable estimate for both provinces combined, because it modeled all of Nova Scotia (much of which is not within H. squamulosa EOO).

1. In GIS Software:
   1. Use a ‘habitat suitability’ criterion (using a mix of stand, soils, or other data) to produce probability of occurrence (PO) data across the province.
   2. Interpolate the occurrence point data to create a raster of Heterodermia squamulosa known abundance (KA – probably the number of trees) at the same resolution.
   3. Determine the Predicted Abundance, or PA = PO × KA.
   4. Overlay lichen track / survey data.
   5. Convert lichen tracks into points for which spacing corresponds with the cell size of the PO/PA/KA rasters.
   6. Use “extract values to points” to add the PO (0-1), PA (0-??), and KA values (0-??) to the entire set of lichen survey points.
   7. Export as a CSV for use in another program.

2. In R Software:
   1. Isolate data columns with PA and KA values; upload into R.
   2. Install and load rpart package.
   3. Run classification tree analysis with PA as the predictor and KA as the responding variable.
   4. Select 3-10 classes with +/- equal replication of survey points. Record your correction factors for each class. (The number of correctly classified KA values gives the correction factor for that class.)

3. In GIS Software:
   1. Create a new raster from the PA layer using the “reclassify” function, with conditional statements such that PA values corresponding to the classes you identified are multiplied by the corresponding correction factors within that class.
   2. Add up the corrected KA values across all cells for the newly derived raster layer. This represents the population size for the province (/proxy of parts of NS and NB combined).

Based on the above model, calculated estimates for maximum occurrences and maximum host trees are 756 and 937, respectively. This may be a high estimate, because the habitat parameters used in the modelling are likely broader than what the species actually needs.

Appendix 2. Threats calculator assessment for Scaly Fringe Lichen

Species or ecosystem scientific name:

Heterodermia squamulosa

Date:

2021-02-17

Assessor(s):

Dwayne Lepitzki (Moderator), David Richardson (Co-chair), Alain Belliveau (SR writer)
SSC members: Jennifer Doubt, Karen Golinski, André Arsenault, Chris Deduke, Sean Haughian, Marion Barbé
Jurisdictions: Mary Sabine (NB)
External experts: Frances Anderson, Julie McKnight.

Assigned overall threat impact:

B = High

Impact adjustment reasons:

Not applicable

Overall threat comments:

The generation time = 19 years. Therefore, timeframe for severity and timing is 57 years into the future; 31 occurrences comprising 14 subpopulations, 145 trees, total 450–515 mature individuals (~53% of the population is at Cape Split [Scots Bay]; 19.2% Shingle Lake; 5.4% Fundy NP; 4.4% Digby and Hectanooga, 4.2% Tusket River) This lichen is found in wetland and upland habitats on mature hardwood forests on Yellow Birch, Sugar and Red Maple, and White Ash. Overall, a continuing decline very probable. The Cape Split occurrence partially protected (Provincial Park), but adjacent private land not protected.

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