Green-scaled Willow (Salix chlorolepis): COSEWIC assessment and status report 2020

Official title: COSEWIC Assessment and Status Report on the Green-scaled Willow Salix chlorolepis in Canada

Threatened
2020

COSEWIC assessment summary

Assessment summary – November 2020

Common name: Green-scaled Willow

Scientific name: Salix chlorolepis

Status: Threatened

Reason for designation: This long-lived dwarf endemic shrub has a generation time of over 30 years. It occurs exclusively in snowbeds on alpine serpentine outcrops of Mount Albert in Parc national de la Gaspésie, Quebec. The entire population is considered to have fewer than 500 individuals. Continued searches have not revealed additional subpopulations. The population is probably stable at present, but may decline in the future as a result of climate change (particularly due to more frequent or prolonged droughts and increased temperatures).

Occurrence: Quebec

Status history: Designated Threatened in April 2006. Status re-examined and confirmed in November 2020.

COSEWIC executive summary

Green-scaled Willow
Salix chlorolepis

Wildlife species description and significance

Green-scaled Willow (Salix chlorolepis) is a branched dwarf shrub, typically less than 30 cm tall, with erect branchlets. The simple leaves are short-stalked, up to 25 mm long, smooth-margined, egg-shaped, and become hairless with age. The floral bracts are hairless as well, olive green in colour and persist during maturation of the capsule. The catkins are short-stalked and 5 to 13 mm long. The fruit is a short-stalked, hairless capsule that is generally approximately 4 mm long. The generation time for Green-scaled Willow is not well understood but can be estimated at about 30 years.

Distribution

Green-scaled Willow occurs exclusively in snowbeds on the alpine serpentine outcrops of Mount Albert in Quebec where it is endemic.

Habitat

Green-scaled Willow occurs in sparsely vegetated alpine habitats on stabilized serpentine rocky slopes in pebbles and gravel or on thin, dry or moderately moist soils with full sun exposure. It is also occasionally found in bog areas on the summit plateau. The species’ habitat is strongly associated with late-melting snowbeds and with elevations ranging from 825 to 1,050 m.

Biology

Green-scaled Willow is dioecious, having separate male and female plants. It flowers from early July to mid-August, after leaf development. Fruiting begins in the last of week of July and continues until the first frosts (early September). The species is predominantly insect- and wind-pollinated and hybridizes fairly frequently with Short-capsuled Willow. The seeds have a tuft of silky hairs which facilitates wind dispersal.

Population sizes and trends

The number of Green-scaled Willow plants growing on Mount Albert has been estimated at 258 individuals, with potentially as many as 500 individuals. Most sites within subpopulations generally have only one or two plants. The largest subpopulation is composed of 136 individuals and another subpopulation has just over 100 individuals. Although not all of the glacial cirques of Mount Albert have been explored, it is believed that the total number of individuals would likely not exceed 500. At one known site, some evidence of declines is observed but identification issues obscure the ability to draw conclusions. One other known site (within a different subpopulation) was not relocated.

Threats and limiting factors

Few threats are currently impacting the species. While signs of herbivory were visible on some willows, the source could not be identified. Models predict reduced precipitation in the region and these projections, in concert with anecdotal reports of notably dry sites in recent years, is cause for some concern. Whether the frequency of drought is increasing is uncertain. Given the occurrence of this species in areas with late-melting snowbeds, climate change can be considered a potential threat, but more research is needed to determine the magnitude of the effects on this species (e.g., vulnerability to drought).

Green-scaled Willow is limited to serpentine bedrock. Hybridization between Green-scaled Willow and the Short-capsuled Willow is frequent on Mount Albert and the risk of introgression with Short-capsuled Willow requires further study. Woodland Caribou can trample and potentially browse on Green-scaled Willow but have always been in the area. Rusty Tussock Moth has been observed on numerous plants, causing severe damage on a few individuals. Galls caused by an insect have been observed on several plants as well, which affects the vigour of individuals. Sawfly larvae have also been noted feeding on the species.

Protection, status and ranks

Green-scaled Willow was assessed as Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 2006 and was listed on Schedule 1 of the Species at Risk Act in 2007. The species was designated Threatened and has been protected under the Quebec Act Respecting Threatened or Vulnerable Species since 1995.

L’habitat floristique de la Serpentine-du-Mont-Albert, created in 1995, provides protection for four threatened plant species, including Green-scaled Willow. The global population of this species is located within Parc national de la Gaspésie.

Technical summary

Salix chlorolepis
Green-scaled Willow
Saule à bractées vertes
Range of occurrence in Canada (province/territory/ocean): Quebec (Mount Albert)

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

Quantitative analysis

Probability of extinction in the wild is at least [20% within 20 years or 5 generations, or 10% within 100 years]? Not 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: high-low
Droughts (high-low – IUCN 11.2)
What additional limiting factors are relevant?
Habitat specificity, risk of introgression, galls affects the vigour, trampling by Woodland Caribou and browsing by Rusty Tussock Moth.

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

Data sensitive species

Is this a data sensitive species? No

Status history

COSEWIC Status History: Designated Threatened in April 2006. Status re-examined and confirmed in November 2020.

Recommended status and reasons for designation

Recommended status: Threatened

Alpha-numeric code: D1

Reasons for Designation: This long-lived dwarf endemic shrub has a generation time of over 30 years. It occurs exclusively in snowbeds on alpine serpentine outcrops of Mount Albert in Parc national de la Gaspésie, Quebec. The entire population is considered to have fewer than 500 individuals. Continued searches have not revealed additional subpopulations. The population is probably stable at present, but may decline in the future as a result of climate change (particularly due to more frequent or prolonged droughts and increased temperatures).

Applicability of criteria

Criterion A (Decline in Total Number of Mature Individuals): Not applicable. Data are lacking to determine a percentage of reduction.

Criterion B (Small Distribution Range and Decline or Fluctuation): Not applicable. Although both EOO and IAO are below thresholds for endangered, no other subcriteria are met: the population is not severely fragmented, and the location concept does not apply due to uncertainty of timing and impacts of threats (a); a continuing decline in EOO, IAO, habitat quality, locations or number of mature individuals does not apply, although there is some likelihood of future decline in habitat quality projected based on climate change, (b); and the population does not exhibit extreme fluctuations (c).

Criterion C (small and declining number of Mature Individuals): Not applicable, is close to meeting Endangered, C2a(i). However, while the number of mature individuals is currently small and below thresholds, the population appears stable, and information is insufficient to project future declines.

Criterion D (Very Small or Restricted Population): Meets Threatened, D1 with an estimated number of individuals below 1000. Does not meet Threatened D2 because it is unlikely that a single threatening event could rapidly affect all of the population within a short period.

Criterion E (Quantitative Analysis): Not applicable. Not done.

Preface

Green-scaled Willow (Salix chlorolepis) was initially assessed as Threatened by COSEWIC in April 2006. The recovery strategy was posted in 2011 and the action plan in 2015 (Environment Canada 2011, 2015).

During a survey conducted in 2018, one new site was found and some poorly described sites not visited in 2004 were relocated and georeferenced. At the other sites, all of the plants that had been observed in 2004 were found again, except for those at the southwesternmost site on Mount Albert (see Sampling Effort and Methods). According to the Centre de données sur le patrimoine naturel du Québec (CDPNQ 2018), one site in the glacial cirque on the western edge of the Vallée du Diable has 200 individuals. In 2018, there were at least 124 individuals at this site. Given that the time of the survey was in late July of 2018, and part of the site was still covered with snow, it is likely that the abundance at this site is roughly the same. In the same year, Green-scaled Willow population was estimated at 258 plants, including 30 males.

According to the available field data, the number of plants in most subpopulations seems stable and significant fluctuations do not occur. The one exception is the site that the Parc national de la Gaspésie has been monitoring in the Grande Cuve area since 2010 through a survey conducted every five years. Data obtained from a visit to this site in 2018 suggest a significant decline in the number of plants growing there. In 2010, a study of 95 individuals marked with metal tags revealed a mortality rate of 53% over a period of 8 years. Adding uncertainty to these results, however, further inspection revealed that only 26 of the remaining 45 living individuals observed in 2018 had been identified correctly as Green-scaled Willow, while the other 19 more densely pubescent plants were classified as hybrids.

The new survey work revealed a few pollinator insect species: Andrenidae (Andrena sp.), an ant Formica sp., a leaf beetle in the genus Syneta (likely Syneta ferruginea) and a rare syrphid fly (Temnostoma venustum) which forages on flowers and whose larvae feed on aphids. A sawfly larva (Hymenoptera, suborder Symphyta) was observed in September.

Geospatial analysis made it possible to better identify the habitat of Green-scaled Willow, and aerial imagery from DigitalGlobe showed that nearly all of Green-scaled Willow sites were already snow-covered at the time the images were taken (October 13, 2016). The main snowbeds on Mount Albert, which expand rapidly in the fall and thaw late in the spring, can be seen clearly on the images, including a number of beds that have not yet been explored.

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 (2020)

Wildlife Species

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

Extinct (X)

A wildlife species that no longer exists.

Extirpated (XT)

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

Endangered (E)

A wildlife species facing imminent extirpation or extinction.

Threatened (T)

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

Special Concern (SC)*

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

Not at Risk (NAR)**

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

Data Deficient (DD)***

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

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
** Formerly described as “Not In Any Category”, or “No Designation Required.”
*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006.
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: Salix chlorolepis Fernald in Rhodora 7:186. 1905.

Pertinent Synonyms: None

English Name: Green-scaled Willow; Green-bracted Willow (Argus 2010)

French Name: Saule à bractées vertes

Family Name: Salicaceae (willow family)

Green-scaled Willow is a member of a genus of approximately 450 species, including 113 in North America (Argus 2010). There is some controversy surrounding the taxonomic status of Green-scaled Willow. Dorn (1976) believes that it is a hybrid between Short-capsuled Willow (Salix brachycarpa) and Bog Willow (Salix pedicellaris), whereas Argus (1965, 1997) suggested that it may be a hairless form of Short-capsuled Willow. The most recent and authoritative review of Salix in North America (Argus 2010), however, concludes that Green-scaled Willow is a full species and that interpretation is followed here.

Morphological description

Green-scaled Willow is a branched dwarf shrub with erect branchlets (Figure 1a), which generally grows to a height of 10 to 30 cm and sometimes 100 cm (Fernald 1905). A detailed description of some morphological characters of Green-scaled Willow is available in Argus (1965, 2004, 2010).

Green-scaled Willow is characterized by its general glabrousness (i.e., hairlessness; Argus 2010). Argus (1965) used the following seven criteria to distinguish Green-scaled Willow from Short-capsuled Willow (Table 1).

Significance

Serpentine soils are often observed to alter the appearance and function of a plant species. These alterations, combined with the isolation characteristic of serpentine habitats, can favour the formation of new species (Proctor and Woodell 1975). The co-occurrence of serpentine soils and alpine tundra habitat is rare in northeastern North America, and Green-scaled Willow is one evolutionary result of this combination (Rune 1954). Green-scaled Willow is one of a series of endemic or disjunct taxa found in the mountains of Parc national de la Gaspésie, highlighting the evolutionary importance of this region for Canada.

The species has no known commercial or medicinal uses, and no evidence of Aboriginal use was found during the preparation of this report.

Distribution

Global range

Green-scaled Willow has been found exclusively on the alpine serpentine outcrops of Mount Albert in Parc national de la Gaspésie, Quebec (Figure 2) and thus is endemic to the Gaspé Peninsula region of eastern Canada (Labrecque and Lavoie 2002; COSEWIC 2006; Argus 2010; Tardif et al. 2016). To date, it has been found on the summit plateau and on the sides of 10 glacial cirques on Mount Albert, which can be delineated into four distinct subpopulations (Figure 3). See Sampling Effort and Methods for more discussion and interpretation of subpopulations.

A few Short-capsuled Willow specimens were found in 2004 at the top of a talus slope at an elevation of 650 m in a small area of serpentine-rich rock, and was suspected in an area 1.5 km long at Mont du Sud, 12 km southwest of Mount Albert. The visit to the latter site was too brief in 2004 to allow the participants to find individuals, but the site is believed to have good potential for Green-scaled Willow, despite its elevation below 800 m (see Habitat Requirements).

Extent of occurrence and area of occupancy

The extent of occurrence (EOO) is 7.9 km². The index of area of occupancy (IAO) is 24 km² calculated using 2 km x 2 km grid squares. COSEWIC guidelines state that if EOO is less than IAO, EOO should be changed to equal IAO to ensure consistency with the definition of IAO as an area within EOO. This calculated current EOO reflects a slight decrease from 8.8 km² in the previous status report due to the loss of one site, despite a thorough search (see Sampling effort and methods).

Search effort

Search effort in 2018 was spread over three work days, specifically July 20 and 21 and September 4. The visits were limited to returning to known sites, and no additional areas were surveyed. A GPS waypoint was taken for each individual and its gender noted whenever possible (see Figure 4). In all, a distance of about 74 km was covered on foot on Mount Albert, representing approximately 42 hours of on-site search effort.

English translations below:

mâle = male
femelle = female
végétatif = individual in the vegetative phase
trajet = route
Site connu = known site

A number of serpenticolous species also occur on Mount Olivine, which is in Parc national de la Gaspésie, 2 km east of Mount Albert. However, a visit to the mountain in 2002 did not reveal any specimens of Green-scaled Willow. The site, which measures 1.7 km long by 600 m wide, is on the summit and east side of the mountain. It is unlikely that Green-scaled Willow occurs at the site because it is located at an elevation of approximately 670 m (which is lower than is typical for this species, see Habitat Requirements).

The habitat of Green-scaled Willow was more precisely identified by analysis of aerial imagery from DigitalGlobe, which showed that nearly all of the Green-scaled Willow sites were already snow-covered at the time the images were taken (October 13, 2016). The main snowbeds on Mount Albert, which expand rapidly in the fall and thaw late in the spring, can be seen clearly on the images, including a number of beds that have not yet been explored.

Habitat

Habitat requirements

Green-scaled Willow grows in sparsely vegetated, serpentine slopes among pebbles and gravel or on thin, dry, or moderately moist soils with full sun exposure (Lavoie and Fleurbec 1995; Coursol 2001). In 2004, several specimens were found on slightly emergent serpentine boulders in the middle of an intermittent stream.

Historical collections mention the presence of Green-scaled Willow in bog areas on the summit plateau of Mount Albert (Lavoie and Fleurbec 1995), yet no individuals were detected on the summit plateau in 2004 despite surveying many kilometres of transects In 2018, only two female plants in a single site were found on the summit plateau (site shown in Figure 5). Mapping of Green-scaled Willow revealed that the species is found more readily in areas with late-melting snowbeds than bog areas (Figure 4).

Green-scaled Willow habitat is strongly associated with elevations ranging from 825 to 1,050 m, and exhibits a large concentration of individuals found at elevations of 925 to 950 m (Figures 2 and 3).

Habitat trends

There has been no apparent decline in habitat quantity or quality at most sites visited since the last status report (COSEWIC 2006) in terms of disturbance from hikers. However, there is some concern with the possibility of future declines in habitat suitability due to climate change; e.g., the NatureServe Climate Change Vulnerability Index (CCVI) for this species is “Highly vulnerable” (Gendreau et al. 2016). This ranking is consistent with observations that the habitat on Mount Albert has been noted to be very dry recently. Whether the frequency of drought is increasing is uncertain but possible given climate projections.

Biology

Green-scaled Willow has separate male and female plants that flower from early July to mid-August, after leaf development. Fruiting begins in the last week of July and continues until the first frosts (early September). Few studies have been conducted on Green-scaled Willow, and most observations come from Argus (1965) and from the surveys conducted by the report writer in the summers of 2004 and 2018. Although the lifespan of this shrub species is unknown, other dwarf shrub species in the genus Salix can live for 42-63 years (Schweingruber and Poschlod 2005). Green-scaled Willow is thought to start flowering after several years (estimated as eight years). By extrapolating maximum lifespan from closely related species, a rough estimate of generation time can be estimated at 30 years using IUCN guidelines (Age of first reproduction + [z * (length of the reproductive period)]; IUCN 2017).

Life cycle and reproduction

Green-scaled Willow appears to have a strongly female-biased sex ratio. Studies of the genus Salix show that the ratio of females to males can be as high as 4:1 (USDA 2004). Based on the number of male and female plants counted on Mount Albert during the two visits in July 2018, the proportion of males in the population is about 14%. Identifying male plants is difficult outside the flowering period and only one individual was identified in the September survey. The species depends primarily on insect pollination. In 2018, four insect species were observed near the catkins of Green-scaled Willow (Figure 6) (see Interspecific Interactions). Wind also plays a role in pollination, especially on bare areas of Mount Albert, as large quantities of pollen can be transported by wind (Argus 1965).

Hybridization between Green-scaled Willow and Short-capsuled Willow is frequent on Mount Albert (Salix × gaspeensis). Further, hybridization between Green-scaled Willow and Bog Willow produces a putative hybrid that has relatively small, glabrous leaves (Argus 2010). Although a number of hybrids were observed during the 2004 and 2018 inventory, it is difficult to determine whether Green-scaled Willow is adversely affected by hybridization (Lavoie and Fleurbec 1995). Green-scaled Willow appears to have persisted despite continued introgression with the Short-capsuled Willow, and further studies on this phenomenon are needed to understand whether the frequency of introgression is increasing.

Physiology and adaptability

Like other plant species associated with serpentine, Green-scaled Willow is adapted to ultrabasic soils with large concentrations of heavy metals, particularly magnesium. In serpentine rock formations, heavy metal concentrations reach levels that are toxic to most plants. Under these conditions, a species-poor vegetation composed of only a few tolerant species becomes established (Proctor and Woodell 1975). This loss of diversity is exacerbated at higher altitudes by the freeze-thaw cycle (congeliturbation). Congeliturbation stirs and churns the soil, limiting the establishment of vegetation through a strictly mechanical effect (Sirois 1984). This effect combines with the increased toxicity caused by the rise of heavy metals to the surface. Plants associated with serpentine are poor competitors that take advantage of regularly disturbed, underdeveloped substrates on which other plants are unable to become established (Sirois 1984).

Specimens maintained in cultivation at the Montreal Botanical Garden since 2004 and in a private garden since 1994 retain their short stature and show no signs of disease, despite the more favourable climatic conditions (Gaudreau pers. comm. 2019).

Dispersal and migration

The seeds have a tuft of silky hairs that facilitates long-distance wind dispersal. They are believed to be able to germinate shortly after dispersal, i.e., within 12 to 24 hours (Argus 1997), and they remain viable for 9 to 10 months (Argus 1997). According to Densmore and Zasada (1983), the seeds of the closely allied Short-capsuled Willow can overwinter and germinate the following spring and this presumably applies to Green-scaled Willow as well.

Interspecific interactions

A few pollinating taxa have been observed on the catkins of Green-scaled Willow. In 2018, four insect species were observed near catkins (Figure 6): an Andrenidae (Andrena sp.), an ant Formica sp. (Ouellette pers. comm. 2018), a leaf beetle in the genus Syneta (Coleoptera: Chrysomelidae: Synetinae), which is probably Syneta ferruginea (Le Tirant pers. comm. 2018), and a rare syrphid fly (Temnostoma venustum) that forages in flowers and whose larvae feed on aphids (Skevington pers. comm. 2018). A hymenopteran larva of a sawfly (suborder Symphyta; more precise identification not possible; Figure 6) was observed on the second visit in September 2018 (Larrivée pers. comm. 2018).

Population sizes and trends

Sampling effort and methods

The 2004 survey was conducted in 10 glacial cirques to provide more information on the distribution and abundance of Green-scaled Willow within certain areas of Mount Albert. The positions of most specimens were recorded using a hand-held GPS device. In 2004, approximately 45 hours of fieldwork were carried out on Mount Albert to locate new occurrences and better characterize previously known occurrences. During the 2018 survey, a new site was found on the plateau, and the plants at the three poorly identified sites that had not been visited in 2004 were counted and georeferenced. Approximately 42 hours of fieldwork were conducted to relocate these sites. A few individuals observed in the 2004 survey on the subpopulation of the south side of Mount Albert were not visited due to field time constraints (Figures 3 and 4). The southwesternmost site was revisited but no Green-scaled Willow was observed despite an extensive search.

In 2004, the number of Green-scaled Willow plants on Mount Albert was estimated at about 300 mature individuals. In 2018, 258 mature individuals were found. While most sites generally have only one or two individuals, some have four or five according to the CDPNQ, and one particular site in the glacial cirque at the western edge of the Vallée du Diable (part of Subpopulation 2) is much larger. At this site, the 2004 survey found 60 individuals between 900 m and 930 m, but no inventory was conducted at lower elevations. In late July 2018, there were at least 124 individuals at this site despite part of the site being still covered with snow.

Outside the Vallée du Diable, the species is found in four glacial cirques on the south side of the south summit of Mount Albert and on the side of the Plaqué Malade Lake glacial cirque. The sites where Green-scaled Willow is present have been grouped into four distinct subpopulations (or element occurrences, NatureServe 2004) based on a minimum separation distance of about 1 km between adjacent subpopulations (Figure 3). Subpopulation 3 could be considered two separate subpopulations on either side of the slope (i.e., if the distance between the northeast and east clusters of sites incorporated elevation), but is considered to be a single subpopulation for the purposes of this report.  

Although Green-scaled Willow was previously reported from historical records on the plateau of Mount Albert (Lavoie and Fleurbec 1995), no plants were found in the 2004 inventory despite several kilometres of transects covered between the north and south summits of Mount Albert. The 2018 survey found only two individuals on the plateau despite several kilometres of transects between the various sites (Figure 4).

Abundance

The confirmed Green-scaled Willow population totals a minimum of 258 individuals, including 30 males. At the time of the visit in July 2018, part of the main site on Mount Albert was still covered with snow. Several individuals were identified solely on the basis of their buds but the sex could not be determined. The counts obtained are nonetheless fairly consistent with the previous population estimates for this site. Even using an extremely optimistic extrapolation, the total number of Green-scaled Willow plants on Mount Albert likely would not exceed 500.

Fluctuations and trends

The numbers reported for the entire Green-scaled Willow population suggest minimal fluctuations, with some caveats that should be considered. In 2004, the number of Green-scaled Willow plants on Mount Albert was estimated at about 300. However, this estimate is now considered erroneous because many specimens are now known to be misidentified, making comparisons between surveys difficult.

There is some evidence of decline within the largest subpopulation. Parc national de la Gaspésie has been monitoring a site every five years in the Grande Cuve since 2010. The data gathered in 2018 shows a substantial decline in the number of individuals at this site. In 2010, 95 individuals were marked with metal tags. In 2015, 27 dead plants were observed (68 remained alive), and in 2018, the 68 tagged individuals were found again and another 23 plants had died, for a mortality rate of 53% over 8 years. Further inspection, however, revealed that only 26 of the remaining 45 living individuals observed in 2018 had been identified correctly as Green-scaled Willow, while the other 19 more densely pubescent plants were classified as hybrids, leaving much uncertainty in how to interpret these results. It is unknown how many of the original 95 individuals were hybrids. While it would seem that individuals at this site have experienced high mortality rates recently, it is possible that the individuals that died were disproportionately composed of hybrids.

Elsewhere, individuals found at sites in 2004 were rediscovered in 2018, except for the individuals growing at the site on the south side of the south summit of Mount Albert, giving an overall impression of only modest declines.

Rescue effect

Not applicable. The species is a narrow endemic known only from Mount Albert.

Threats and limiting factors

The threat classification below is based on the International Union for Conservation of Nature and the Conservation Measures Partnership unified threats classification system (see Master et al. 2012). The overall threat was estimated to be High-Low, reflecting the uncertainty of the impact of climate change on this species.

Threats

IUCN Threat 11. Climate change and severe weather (high-low)

11.2 Droughts

The NatureServe CCVI for this species is considered “Highly vulnerable” (Gendreau et al. 2016), likely due to its narrow restriction to serpentine soils leading to projections that the species will be exposed to conditions in the future that are different from its historical niche. There is still much uncertainty regarding how vulnerable Green-scaled Willow will be to the increase in temperature and decrease in precipitation predicted for the region, but high mortality rates at one site and anecdotal observations of dry years recently are worrisome. Whether the frequency of drought is increasing is uncertain and will require continued monitoring. The species is considered to be to be experiencing declines at a site in Parc national de la Gaspésie, where climate change is considered to be playing a role in the high mortality rates observed. More research is needed to determine the effects of drought on Green-scaled Willow.

IUCN Threat 6. Human intrusions and disturbance (negligible)

6.1 Recreational activities

The managers of Parc national de la Gaspésie are attempting to control the impact of hikers along the Appalachian Trail which runs adjacent to the most important site for Green-scaled Willow on Mount Albert. The trail was moved in 2005. Owing to the abundant snowfall in July 2018, hikers moved off-trail into snow-free areas. A few cases of mortality observed in the Grande Cuve area by park staff could be explained in part by trampling.

IUCN Threat 10. Geological events (negligible)

10.3 Avalanches/landslides

Off-trail downhill skiing is gaining in popularity, and skiers may eventually want to use other sectors of Mount Albert. This would require an assessment of the potential severity of disturbances to Green-scaled Willow habitat associated with avalanches, but this threat appears to be low or non-existent.

Limiting factors

Green-scaled Willow is limited by its restriction to serpentine bedrock and also possibly by hybridization with closely related species (see Life Cycle and Reproduction). Hybridization occurs readily with Salix brachycarpa (Short-capsuled Willow), which is a common species in the area. Currently, there is no evidence that humans have altered the distribution of Salix brachycarpa so suggesting that hybridization is better considered a limiting factor than a threat. As well, Green-scaled Willow is impacted by the following interspecific interactions.

Trampling by Woodland Caribou

Woodland Caribou (Rangifer tarandus caribou), Gaspésie-Atlantic population, is listed as Endangered on Schedule 1 of the Species at Risk Act. This mammal frequents Parc national de la Gaspésie, including Mount Albert, but is decreasing in abundance (Environment Canada 2011). These animals are considered likely to trample Green-scaled Willow plants during their movements on Mount Albert. The impact of this trampling cannot be assessed at present, however, based on observations of (light) trampling impact on the associated tundra vegetation. During summer heat waves, Woodland Caribou move to areas with snow patches to cool off. In late July 2018, a few Woodland Caribou were observed on the snow layer covering the upper part of the Grande Cuve site, which is where the largest Green-scaled Willow site is found. When these caribou moved out of the snow-covered area, they were observed walking on Green-scaled Willow plants; however, no visible damage was evident.

Browsing by Woodland Caribou

While the winter diet of Woodland Caribou consists primarily of lichens, in summer these animals feed on sedges, forbs, dicotyledonous plants, lichens, fungi, and the leaves of shrubs, primarily willows (Moisan 1956; COSEWIC 2002). It is therefore probable that Woodland Caribou feed on the leaves of Green-scaled Willow plants, although the extent of this is not known. Browsing by caribou was not identified as a threat in the 2006 COSEWIC status report, and this behaviour was not observed in 2018.

Browsing by Rusty Tussock Moth

Rusty Tussock Moth (Orgyia antiqua L., a native species in Quebec) was observed several times on Green-scaled Willow and Short-capsuled Willow plants during the 2004 survey. The foliage of a few individuals showed severe damage. Although presently it is impossible to determine the impact of herbivory by these moths on the Green-scaled Willow population, it appears to be relatively low (McIntosh pers. comm. 2006) and the impact of Rusty Tussock moth herbivory is unlikely to be fatal for willow plants. Although this insect species was not observed in 2018, insect-damaged capsules were noted on a few plants.

Diseases of unknown origin

Galls of unknown origin were noted on Green-scaled Willow and Short-capsuled Willow plants several times in 2004 and 2018. These irregular galls are likely caused by mites or aphids (Goulet 2005). The impact on Green-scaled Willow is unknown, but Sacchi et al. (1988) reported that flower bud production was reduced by 43% in affected plants compared to buds on intact stems and that seed production per individual was reduced by between 10% and 50% in Arroyo Willow, Salix lasiolepis. In a study on the impact of galls on the Snowbed Willow (Salix herbacea), Hakkarainen, Roininen and Virtanen (2005) showed that the mortality of galled shoots was approximately 40% higher, and the mortality of galled ramets approximately 25% higher, than in the control ramets and in the leaf removal treatment. The leaf biomass of galled ramets and the number of leaves were significantly lower in galled ramets than in untreated or leaves-removed ramets. It is possible that galling causes fatal resource depletion of shoots in its host plant. The results show that leaf gallers are ecologically more influential than previously thought (Hakkarainen, Roininen and Virtanen, 2005).

Number of locations

For the purposes of this COSEWIC assessment, locations are defined by the scale of the most serious and plausible threat to Green-scaled Willow. Climate change is the main threat to the individuals on Mount Albert, which would impact all subpopulations to some degree. It is difficult to assess the extent of the population that would be impacted within a single generation (~30 years), but it is likely that some mortality would be observed throughout the entire population, which provides justification for there being one location in Canada.

Protection, status and ranks

Legal protection and status

Green-scaled Willow was assessed as Threatened by COSEWIC on April 29, 2006 and listed as such on Schedule 1 of the Species at Risk Act on December 13, 2007. The species has also been protected since 1995 by the Quebec Act Respecting Threatened or Vulnerable Species (LEMV), under which it is listed as Threatened.

Non-legal status and ranks

Green-scaled Willow is ranked as Critically Imperilled globally (G1), nationally (N1, in Canada) and provincially (S1, in Quebec) by NatureServe (2018).

Habitat protection and ownership

L’habitat floristique de la Serpentine-du-Mont-Albert, created in 1995, provides for the protection of Green-scaled Willow and other threatened plant species.

The Canadian population is located within the boundaries of Parc national de la Gaspésie.

Acknowledgements and authorities contacted

The report writer would specifically like to thank the following people:

Claude Isabel. Chief (manager), Conservation and Education, Parc national de la Gaspésie

Jacques Labrecque. August 2018. Botanist, Centre de données sur le patrimoine naturel du Québec, Direction de la protection des espèces et des milieux naturels, Ministère de l’Environnement et de la Lutte contre les changements climatiques du Québec

Maxim Larrivée. December 2018. Chef de division, Insectarium de Montréal, Espace pour la vie

Stéphane Le Tirant. December 2018. Collections entomologiques et recherche, Insectarium de Montréal, Espace pour la vie

Pascal Lévesque. 2018. Director, Parc national de la Gaspésie

Dominic Ouellette. December 2018. Entomologist, Insectarium de Montréal, Espace pour la vie

Jeff Skevington. Research Scientist, Canadian National Collection of Insects, Arachnids and Nematodes (CNC), Agriculture and Agri-Food Canada

Thanks also to the botanists Virginie Laberge and Philippe Blais who assisted the report writer with counts during the fieldwork in 2018. Finally, we wish to thank the entomologists who contributed to the identification of insects on Green-scaled Willow in 2018: Stéphane Le Tirant, Maxim Larrivée and Dominic Ouellette of the Insectarium de Montréal and Jeff Skevington of the Canadian National Collection of Insects, Arachnids and Nematodes (CNC). Maps and IAO/EOO calculations were completed by Alain Filion at the COSEWIC Secretariat. Jana Vamosi of the Vascular Plant SSC provided guidance and direction. Many reviewers are thanked for their helpful contributions and suggestions.

Information sources

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Argus, G.W. 1997. Infrageneric classification of Salix (Salicaceae) in the New World. Systematic Botany Monographs 52:1-121.

Argus, G.W. 2004. Salix of North America, ActKey. Web site: http://flora.huh.harvard.edu:8080/actkey/actkey.jsp?setId=3390 [accessed January 2005]. (presently not an active link)

Argus, G.W. 2010. Salix chlorolepis. In: Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 16+ vols. New York and Oxford. Vol. 7, p. 85. [Accessed September 2018].

Centre de données sur le patrimoine naturel du Québec (CDPNQ) 2018. SGBIO. Ministère du Développement durable, de l’Environnement et de la Lutte contre les changements climatiques, Gouvernement du Québec, Québec. [restricted access, accessed June 2018].

COSEWIC. 2002. COSEWIC assessment and update status report on the woodland caribou (Rangifer tarandus caribou) in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa. xi + 98 p.

COSEWIC. 2006. COSEWIC Assessment and Status Report on Green-scaled Willow (Salix chlorolepis) in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + p. 22.

Coursol, F. 2001. Fiche d’information sur le saule à bractées vertes. Gouvernement du Québec. Web site: http://www.menv.gouv.qc.ca/biodiversite/especes/saule/saule.htm. (presently not an active link)

Densmore, R. and J. Zasada. 1983. Seed dispersal and dormancy patterns in northern willows: ecological and evolutionary significance. Canadian Journal of Botany 61: 3207-3216.

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Environment Canada. 2015. Action Plan for the Green-scaled Willow (Salix chlorolepis) in Canada. Species at Risk Act Action Plan Series. Environment Canada, Ottawa. iv + 11 p.

Fernald, M. L. 1905. An anomalous alpine willow. Rhodora 7:185-186.

Gaudreau, L. pers. comm. 2019. Email correspondence to F. Coursol. September 2019. Biologist and retired director of the Direction générale du développement durable et du patrimoine écologique, Ministère de l’Environnement du Québec, Gouvernement du Québec, Québec, Quebec.

Gendreau, Y., A. Lachance, H. Gilbert, N. Casajus & D. Berteaux. 2016. Analyse des effets des changements climatiques sur les plantes vasculaires menacées ou vulnérables du Quebec. Bureau d’écologie appliquée. 39 pages + 5 annexes.

Goulet, H. pers. comm. 2005. Email correspondence to André Payette, February 2005, Insect and Arachnid Systematics, Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Government of Canada, Ottawa, Ontario.

Hakkarainen, H., H. Roininen, & R. Virtanen. 2005. Negative impact of leaf gallers on arctic-alpine dwarf willow, Salix herbacea. Polar Biology, 28:647-651.

IUCN. 2017. Guidelines for Using the IUCN Red List Categories and Criteria. Version 11. Prepared by the Standards and Petitions Subcommittee. http://www.iucnredlist.org/documents/RedListGuidelines.pdf. (presently not an active link)

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Larrivée, M. pers. comm. 2018. Email correspondence to F. Coursol. December 2018. Chef de section - Collections entomologiques et recherche, Insectarium de Montréal/Espace pour la vie, 4581 Sherbrooke St. E., Montréal, Québec, H1X 2B2

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McIntosh, R. pers. comm. 2006. Rory McIntosh, Ph.D., insect and disease specialist for the Saskatchewan Forest Service, provided an assessment of the impacts of herbivory on Salix chlorolepis by Rusty Tussock Moth, which was submitted to Rob Wright, Ph.D. (member of COSEWIC, Saskatchewan) at the April 2006 COSEWIC Species Assessment Meeting.

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Ouellette, D. pers. comm. 2018. Email correspondence to F. Coursol. December 2018. Insectarium de Montréal, Espace pour la vie, Montréal, Quebec.

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Rune, O. 1954. Notes on the flora of the Gaspé Peninsula. Svensk Botanisk Tidskrift 48:117-136.

Sacchi, C.F., P.W. Price, T.P. Craig and J.K. Itami. 1988. Impact of shoot gall attack on sexual reproduction in the arroyo willow. Ecology 69(6):2021-2030.

Schneider, C. 1918. Notes on American willows. II, The species related to Salix glauca L. Botanical Gazette 66:318-353.

Schneider, C. 1922. Notes on American willows. XII, Systematic enumeration of the sections, species, varieties, and forms of American Willows. Journal of the Arnold Arboretum 3:61-125.

Schweingruber F. and P. Poschlod. 2005 Growth rings in herbs and shrubs: lifespan, age determination and stem anatomy. Forest Snow and Landscape Research 79:195–415.

Skevington, J. pers. comm. 2018. Email correspondence to M. Larrivée. December 2018. Insectarium de Montréal, Espace pour la vie, Montréal, Quebec.

Sirois, L. 1984. Le plateau du mont Albert, Étude phyto-écologique. Master’s thesis, Laboratoire d’écologie forestière, Faculté de Foresterie et de géodésie, Université Laval, Sainte-Foy, Quebec, 152 p.

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Biographical summary of report writer(s)

Frédéric Coursol received a degree in biological sciences from the Université de Montréal in 1992. He has written five status reports on threatened or vulnerable species in Quebec (Saururus cernuus, Onosmodium molle var. hispidissimum, Cicuta maculata var. victorinii, Gentianopsis victorinii and Eriocaulon parkeri). For COSEWIC, he participated in the drafting of status reports on the Quebec Rockcress (Boechera quebecensis), Serpentine Stitchwort (Minuartia marcescens), and Parker’s Pipewort (Eriocaulon parkeri) and update status reports on Provancher’s Fleabane (Erigeron philadelphicus var. provancheri), Victorin’s Gentian (Gentianopsis virgata subsp. victorinii), Victorin’s Water-hemlock (Cicuta maculata var. victorinii) and Anticosti Aster (Symphyotrichum anticostense), the latter in collaboration with Jacques Labrecque and Luc Brouillet. His knowledge of estuarine taxa comes from fieldwork carried out in 1995 for the 2001 report he co-authored with Luc Brouillet and Denis Bouchard on the threatened and vulnerable plants and other rare plants of the upper St. Lawrence Estuary between Grondines and Saint-Jean-Port-Joli. He contributed to the writing of a collective work entitled Plantes rares du Québec méridional, and he provided close to half of the species photographs for that work. Lastly, he assisted in compiling data for VASCAN, the database of vascular plants of Canada. It is a complete list of vascular plants reported in Canada, Greenland (Denmark) and St. Pierre and Miquelon (France).

Collections examined

The only collection reviewed to examine Green-scaled Willow specimens was that of the Université de Montréal (MT) in Montréal.

Appendix 1. IUCN threats assessment on the Green-scaled Willow

Threats assessment worksheet

Species or ecosystem scientific name:

Green-scaled Willow (Salix chlorolepis)

Element ID

Elcode

Elcode

Not applicable

Date:

Not applicable

Assessor(s):

Dave Fraser (moderator), Jana Vamosi (Co-Chair, VP SSC), Frederic Coursol (report writer), Nancy Hebert, Jacques Labreque, Angele Cyr

References:

Not applicable

Assigned overall threat impact:

Not applicable

Impact adjustment reasons:

Not applicable

Overall threat comments

Generation time is unknown for this species but other dwarf shrub species in Salix live for 42-63 years (Schwingrub and Poschlod 2005). Green-scaled Willow is thought to start flowering after several years (estimated as 8 years). A rough estimate of generation time can be assessed as Age of first reproduction + [ z * (length of the reproductive period) ] or 8+0.5(52-8)=30 years.

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