Hoary mountain-mint (Pycnanthemum incanum (L.) Michx.) recovery strategy: chapter 1

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BACKGROUND

1.  Species Information

Date of Assessment:              May 2000

Common Name:                      Hoary Mountain-mint

Scientific Name:                     Pycnanthemum incanum (L.) Michx.

COSEWIC Status:                  Endangered (April 1986)

Reason for Designation:         Two very small nearby populations with drastic decline in plant  numbers and increased threat from exotic plants.

Canadian Occurrence:            ON

COSEWIC Status History:   Designated Endangered in April 1986. Status re-examined and confirmed Endangered in April 1998 and in May 2000. Last assessment based on an existing status report.

1.1  Species Description

Hoary Mountain-mint is one of several species of mountain-mint (Pycnanthemum) found in Ontario.  It is a perennial herbaceous plant that grows to a height of 1 m.  In Ontario, the plants are reproducing largely vegetatively from rhizomes (underground horizontal stems), even though the plants are producing viable seeds.  The stems have many fine white hairs, especially on the upper parts .  In this particular species, the number of stems per plant is an indicator of the age and hardiness of the plant (Obee 1994).  The leaves are opposite.  The main leaves are 5-10 cm long and 1.5-3.5 cm wide.  They are densely hairy on the lower leaf surface and on the upper surface of the leaves in the upper part of the plant.  They have few teeth and a fragrant, minty scent.  The genus is appropriately named Pycnanthemum, which means "densely flowered".  The small, white, purple-spotted flowers are found in dense clusters at the end of stems and in the leaf axils.  The flowers clusters are 1.5 to 3.5 cm in diameter and bloom in mid to late summer. 

2.  Distribution

2.1  Global Range

Hoary Mountain-mint occurs solely in eastern North America.  As illustrated in Figure 1, its range extends from New Hampshire southwest to Missouri and east through Tennessee and Georgia.  However, NatureServe (2005) also reports it from Louisiana, Mississippi, Alabama, and Florida.

2.2  Canadian Range

The only location of this species in Canada is in southern Ontario (Figure 2).  There are five extant sub-populations, extending between Hamilton and Burlington on the Hamilton Harbour shoreline.  This plant is probably so rare in Ontario because it is at the northern extent of its range.

2.3  Percent of Global Distribution in Canada

It is estimated that Canada comprises less than 1% of the species’ global range (Oldham 1997).

2.4  Distribution Trend

There does not appear to have been any significant change in the distribution of this species in Canada over the last 25 years .

3.  Population Abundance

3.1  Global Abundance

The global abundance of this species is unknown, but it is ranked as G5, meaning that it is very common globally and is secure under current conditions.  It is widespread and relatively common throughout a major portion of its range in the eastern United States.  However, three states on the edge of its range (Delaware, New Hampshire, and Vermont) identify it as extremely rare (S1).  In New Hampshire and Vermont it is also listed as Endangered.  It is ranked as common (S4) in North Carolina, very common (S5) in Kentucky and West Virginia, and under review (SU) in Florida.  In all other states in its range, Hoary Mountain-mint is ranked SNR, which indicates that it is found in the state but not ranked, probably due to a lack of information.  These states are Alabama, Connecticut, District of Columbia, Georgia, Illinois, Louisiana, Maryland, Massachusetts, Mississippi, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, and Virginia. 

3.2  Canadian Abundance

In Canada, Hoary Mountain-mint is listed as N1, and in Ontario it is listed as S1.  This means that both nationally and provincially it is extremely rare.  It was documented several times between 1885 and 1900 near Burlington, Ontario, but was not seen again until 1981, when it was collected in the same general area.  All current and historical populations were found within a few kilometres of each other in Hamilton and Burlington, Ontario.  There are two extant occurrences (or populations) of Hoary Mountain-mint in Canada, and one recently extirpated occurrence (Table 1).

The largest extant occurrence of Hoary Mountain-mint is in Hamilton on the Burlington Bluffs.  This occurrence consists of 4 sub-populations.  One sub-population is quite large and consists of more than 700 individuals located in along a dry, very steep (and highly unstable) south-facing slope.  The second sub-population consists of 5 stems.  It occurs in a relatively large opening in the forest that could be described as a hanging prairie.  This site is a very steep, south-facing slope dominated by the prairie grasses little bluestem (Schizachyrium scoparium) and big bluestem (Andropogon gerardii) (White 1997).  The other two sub-populations were discovered in 2000.  One consists of approximately 12 plants, while the other consists of approximately 6 plants.  No stem counts were completed at these two subpopulations in 2005.

The second extant occurrence is on the top of a bluff in an oak woodland opening.  In 1984, it consisted of 41 stems; in 2005 there were only 15 stems. 

Table 1.  Summary of Canadian Hoary Mountain-mint Observations Since 1984

*Site – Site codes represent precise locations.  This information has been kept confidential for the protection of the species.

¹ White (1997)

² O’Hara (2001)

³ Unpublished

3.3  Percent of Global Abundance in Canada

The percent of global abundance in Canada is less than 1% (Oldham 1997). 

3.4  Population Trend

Observations of the Hoary Mountain-mint populations were made by several individuals since its rediscovery in 1981 and many of these include stem or plant counts.  These records are compiled in Table 1 and show declines in the three sub-populations that have multiple observations.  The rates of these declines are of great concern.  There has been a 100% loss at Site 3, 87% loss at Site 2a, and 68% loss at Site 1 since they were first recorded.  It is not known if the three sub-populations found in 2000 are evidence of recruitment because there are no previous observations with which to compare them.  There does not seem to be a decline in global population.   

4.  Habitat Identification

4.1  Habitat Needs

Hoary Mountain-mint requires dry, open, sandy-clay habitats in open-canopied deciduous woods on warmer-than-normal slopes (Crins 1986). In Ontario, two out of three habitats in which Hoary Mountain-mint is found are Dry Black Oak-White Oak Tallgrass Woodland Type and the third is Mineral Treed Bluff Ecosite (using the Ecological Lands Classification for Southern Ontario (Lee et al. 1998)).  The habitat data on the labels of historical specimens indicate that this species has been found in open woods (probably oak savanna), roadsides, thickets, pastures, and sunny banks.  The common factor among these sites is that they are normally dry and warm (Crins 1985).  In New Hampshire, this species is found on dry slopes and in pastures, shady clearings, and dry oak forest.  In all cases the species is located on a slope or hill (S. Cairns, pers. comm.).   In North Carolina, the species occurs in woodlands, thickets, old fields, pastures, roadsides, and utility rights-of-way (J. Amoroso, pers. comm.).  Hoary Mountain-mint is much more common and much less habitat-specific at the centre of its range.  

4.2  Critical Habitat

Under the Species at RiskAct, critical habita t is defined as "the habitat that is necessary for the survival or recovery of a listed wildlife species”.  The critical habitat of the extant populations of Hoary Mountain-mint is identified, to the extent possible. M ore critical habitat may be added in the future as new populations are created or as additional information is acquired. 

To achieve the recovery goal of this recovery strategy, the critical habitat for Hoary Mountain-mint includes the immediate locations of the plants and their associated vegetation communities.  These areas have already been mapped using the habitat mapping guidelines for the Conservation Land Tax Incentive Program (Ontario Ministry of Natural Resources 1998) as Occupied Habitats and Endangered Plant Communities.  The communities are Dry Black Oak-White Oak Tallgrass Woodland and Mineral Treed Bluff.  However, further study is needed to determine whether additional habitat is required for population expansion.  A schedule of studies has been identified in section 4.4 to direct this research.      

4.3  Examples of Activities That Are Likely to Result in Destruction of the Critical Habitat

The primary activities that will likely result in destruction of critical habitat are:

·        Activities, such as fire suppression, that create conditions favourable to invading and encroaching plants that shade the Hoary Mountain-mint plants.

·        Activities that increase slumping and instability of the slope due to the processes of natural erosion and slippage caused by groundwater seepage. The lack of vegetative cover on the steep slopes of the largest population accelerates the erosion.  Lake erosion at the base of the bluff causes further slippage of the loose soil.     

·        Dumping of organic and inorganic debris.

·        Trampling from adjacent trail use.

4.4  Schedule of Studies

Further research is needed to evaluate whether the population is large enough to ensure long-term population viability (Table 2).  If it demonstrates that an increase in population distribution is required, additional critical habitat will be identified and mapped. 

Table 2.  Schedule of Studies

* These are tentative dates and may be modified as necessary.

4.5  Habitat Protection/Ownership

One population of Hoary Mountain-mint is under public ownership (provincial Crown land) and the remaining two are under private ownership.  The species is currently listed in regulation under the Endangered Species Act, which protects regulated Endangered species and their habitat from wilful destruction or interference.  Section 2.1 of the Provincial Policy Statement (PPS) issued under the Planning Act does not permit development or site alteration in significant habitat of Threatened and Endangered species.  The recommended approach to determining the impacts of any development applications requires a review of habitat descriptions in the recovery plan, an evaluation of the significant habitat, and consultation with experts and with the Ontario Ministry of Natural Resources (Ontario Ministry of Natural Resources 1999).  The OMNR encourages municipalities to identify significant habitat and protect it through the appropriate zoning category to ensure no development or site alteration occurs.

Hoary Mountain-mint is also listed as Endangered in Schedule 1 of the Species at RiskAct.  This act includes prohibitions against harming the species or destroying its critical habitat on federal lands.  Prohibitions under the Species at RiskAct do not apply to private lands unless an order of the Governor in Council is recommended by the Minister of the Environment.

5.  Biologically Limiting Factors

It is possible that the habitat requirements of this species have prevented it from spreading elsewhere in Ontario.  In addition, the relative isolation of the population, in combination with the small population size, may result in a loss of genetic diversity.  The fact that this species is at the northern edge of its range may also limit its recovery in Canada.  This species is easily propagated and is known to survive in garden settings further north.  It is unknown why the species has not spread and is not encountered more frequently in Ontario. 

There are several potential threats to the Canadian populations of Hoary Mountain-mint.  No studies have been completed to evaluate the degree of these threats.  However, based on site observations and current knowledge, they are listed below in order of significance.    

Succession and Fire Suppression

This species requires sunny openings in dry areas. The loss of habitat through succession of shrubs such as Staghorn Sumac (Rhus typhina), Grey Dogwood (Cornus racemosa), Riverbank Grape (Vitis riparia), Black Raspberry (Rubus occidentalis), and Choke Cherry (Prunus virginiana) is also a recognized threat.  An increase in canopy cover has likely decreased the size of some populations, and over-shading has limited spread to the surrounding areas.  Fire suppression may be contributing to the succession of shrubs and trees.  At one site, a long-time land manager recalled at least two grass fires during his lifetime where Hoary Mountain-mint is present.  It is likely that periodic fires helped keep the canopy open and amenable to Hoary Mountain-mint and several prairie species. 

Invasive Species

All populations of Hoary Mountain-mint are threatened by the encroachment of alien species.  There is an unusually high diversity of exotic woody plants in the area, reflecting the intensive horticultural development adjacent to the slopes that support Hoary Mountain-mint.   The species’ habitat is home to many non-native shrubs, including Tartarian Honeysuckle (Lonicera tatarica) and Buckthorn (Rhamnus cathartica).  Some native willows (Salix eriocephala) were planted on parts of the slope in the early 1980s to combat erosion, and they are one of several species that are encroaching on the habitat of the  Hoary Mountain-mint.  In addition to a dense shrub layer, much of the wooded area along the bluffs has been colonized by Garlic Mustard (Alliaria petiolata).  These factors have led to a loss of diversity in native flora at the site.  It is likely that Hoary Mountain-mint is affected by competition with invasive species, which have already colonized large areas of the bluffs and have resulted in the extirpation of the population of Hoary Mountain-mint at Site 3.  

Slumping

Some of the populations occur on very steep and highly unstable south-facing bluffs, which are difficult to access. The presence of numerous groundwater seepage areas along the bluffs contributes to internal stability problems.  There is evidence of slumping above and adjacent to some populations.  One population that occurs in this type of area has been reduced drastically in size since its discovery.  The decline could be due to slumping or erosion of the steep slope. It is possible that the largest clump of plants at this site was close to the edge and it may have fallen over the bank (D. Kirk, pers. comm.).  Although slumping may be a threat to established populations of Hoary Mountain-mint, it may also be of benefit by creating openings in the canopy under which new Hoary Mountain-mint plants could colonize.

Dumping and Development

The dumping of garden waste and other materials over the rim of the slope is a common occurrence in the deep valleys surrounding Hamilton Harbour.  Many of these areas are used by local residents as dumping grounds.  This problem has been curbed slightly because of the presence of cemeteries in the area, yet some dumping still occurs.  The source of this dumping is in part from cemetery operations and from cemetery visitors.  It is not uncommon to find plant pots, plastic wreaths, and other assorted materials at the edge of the bluffs, as well as grass and tree clippings. This dumping occurs along the forest edge of the cemetery and may jeopardize the survival of Hoary Mountain-mint.  Dumping of horticultural materials could lead to the introduction of more non-native or invasive species to the area.  In addition, the dumping of waste over the slope could damage plants and disturb their habitat.

Development of the areas near the slope has led to the accumulation of large piles of dirt that are being pushed near to and over the rim of the bluffs.  This activity takes place away from the currently occupied sites, but it may have an impact on the potential habitat of this species.  The bluffs are currently regarded as wasteland by the landowners and the City of Hamilton.  The bluffs are very steep and as they border on the water’s edge, they will never be developed. 

Small Population Size

Due to the low numbers of Hoary Mountain-mint and its limited distribution in Canada, it may be threatened by a small gene pool.  This is of concern, because the plants appear to be reproducing primarily through vegetative means.  Vegetative reproduction produces new stems and plants with an identical copy of the parent’s DNA.  This method of reproduction lowers the genetic diversity of the population, and over generations this reduced genetic diversity can result in a decreased ability to adapt to change and the possible extirpation of the species from Canada.  The genetic diversity among the Canadian populations is unknown and it is therefore difficult to assess the degree of this threat.

 Other Threats

Although some of the landowners are currently aware of the locations of the rare species and Hoary Mountain-mint is currently regulated under the provincial Endangered Species Act, it is possible that individual plants may still be at risk of accidental destruction.  For example, the presence of a trail adjacent to one of the populations may increase the potential of trampling the plants.

Crins (1989) also noted that the fragrance and beauty of the plant, as well as its role in the production of high-quality honey, could potentially put the species at risk of collection by gardeners and apiculturists (although no evidence of collection has been found as of this time).  It has also been noted by the recovery team that the species is in cultivation and is available for sale through a small number of sources.  The origin of the plants and/or seed used for this purpose is unknown.  At this time, the recovery team does not recommend the collection of seed from the native populations of Hoary Mountain-mint for non-scientific purposes or for purposes not sanctioned by the recovery team. 

7.  Ecological Role

The ecological role of this species is unknown at this time.

8.  Importance to People

Like many members of the mint family, this plant has been used to treat colds, fevers, and digestive disorders, especially gas (Foster and Duke 1990).  Its use as a carminative is well established. A leaf tea is usually used as a remedy, but a tincture would also provide the active components (Grieve and Leyel 1996).  The Cherokee used a leaf poultice for headache and they drank leaf tea for heart trouble and to prevent diarrhoea when they ate green corn (Hamel and Chiltowsky 1975). According to Crins (1985), Hoary Mountain-mint has been shown to contain a high natural rubber content, and it may have some potential as a rubber-hydrocarbon crop.  Hoary Mountain-mint is also known to be very attractive to honey bees and could be useful in honey production. Furthermore, other species of mountain-mint have shown odour-blocking and anti-fungal properties, and have been used to flavour soups and meats.  

9.  Actions Already Completed or Underway

This species is currently regulated under the Ontario Endangered Species Act.  This affords protection to the species and its habitat.  The current landowners have been informed of the presence of this species on their land through the regulation process (1986).  All landowners and adjacent landowners must be re-contacted in order to establish a communications network and to identify landowner concerns and opinions.

Some recovery actions have already been attempted informally over the last four years (2001-2005).  Small-scale manual removal of invasive species from the area surrounding one population is ongoing. No assessment of the effectiveness of these actions has taken place.  There have been no recovery actions implemented at the other two sites, apart from the removal of a few shrubs at the "hanging prairie" site.

Seed and plant material were collected by the Royal Botanical Gardens (RBG) in 1999/2000 and preliminary propagation and seedbank studies have been completed.  In addition, plants propagated in 2000 were planted at a demonstration site at the Cootes Paradise Fishway, where they will be used for further research and seed collection. 

Census surveys were conducted in 2000/2001 in areas where there were extant and historical records of Hoary Mountain-mint.  Nearby areas with similar habitat characteristics were also investigated for the presence of previously overlooked plants.  All populations were located to within 1 m using a Global Positioning System.  In addition, representative herbarium specimens were prepared to document each population.  These vouchers are stored at the RBG herbarium (HAM). 

Ecological Land Classification (ELC) surveys were completed for polygons containing Hoary Mountain-mint, noting also the extent of the Occupied Habitat, Endangered Plant Community, and Habitat Protection Zone within or in the vicinity of each polygon, as required for the Conservation Land Tax Incentive Program (CLTIP) (Ontario Ministry of Natural Resources 1998).  Mapping was based on available airphotos, and is stored at the RBG in GIS files.  ELC data included floristic inventory, soil and topographic description, and management/disturbance scoring.  Summaries of adjacent land use were also provided.  Special note was made of any factors that may present a threat to the Hoary Mountain-mint populations. The results of the census and ELC surveys will be used to develop appropriate action plans for Hoary Mountain-mint populations in Ontario. 

Some habitat restoration has begun at one site.  The landowners are attempting to remove invasive species and restore the area to oak savanna and open woodland (O’Hara 2002).

Planning for a prescribed burn at one location was initiated in the fall of 2005.  This effort is being led by the Ministry of Natural Resources – Aurora and Guelph District in cooperation with Halton-Peel Woodlands and Wildlife Stewardship.  Site preparation began in fall 2005 with removal of woody invasives and application of herbicide on stumps.  A successful prescribed burn was undertaken in April 2006 resulting in the clearing of woody debris and invasive species such as periwinkle.  Monitoring continued through 2006 and a follow-up prescribed burn was completed in the spring of 2007.

10.  Knowledge Gaps

Current knowledge of this species is limited to general characteristics and habitat preferences, but it is adequate for the implementation of some recovery actions.  Detailed information on the biology of Hoary Mountain-mint should be collected in order to increase our understanding of the species.  More detailed information on the status of the species and its threats in other localities (United States) would also foster a better understanding of the species and its long-term needs.

10.1  Survey Requirements

Searches of potential habitat and historical locations for populations have been completed.  This led to the rediscovery of the large population on the Burlington Bluffs in 2000 that had not been relocated since 1971. Other areas have been searched and a complete inventory of the entire bluff area was completed in 2001 using Ecological Lands Classification methodology.  It may be worthwhile to search similar habitats along the Lake Ontario shoreline, but further searching is unlikely to turn up any other populations in Ontario, since this species has never been found at any other locality and was once thought to be extirpated in Canada. 

10.2  Biological/Ecological Research Requirements

The germination requirements of this species should be determined.  This plant is known to be in cultivation in Ontario and some native plant growers may have knowledge of the species' germination requirements.  Repeated yearly monitoring of the demography of large populations is needed in order to increase the level of understanding of the life history of the species. This would allow the life span of individual plants and the amount of seedling establishment and mortality to be determined. Threats to the populations could then be assessed on an individualized basis. Monitoring should record population size, area, and an estimation of seed set in a given year. Advances in the successional stage of the surrounding community should be tracked. If there is any intentional or unintentional manipulation of the area in which a population occurs, the effects of the manipulation should be monitored and recorded. Determining quantifiable population goals would also assist the recovery team in evaluating the success of recovery efforts.  

Seed dispersal patterns for this species must be defined.  Seed transport mechanisms for Hoary Mountain-mint are unknown.  Identifying known predators and pollinators of this species may aid in determining the seed dispersal mechanisms used by this species.

10.3  Threat Clarification Research Requirements

In the case of slumping, further research needs to be done on how to improve the stability of the slope that supports the largest population of Hoary Mountain-mint.   It is believed that the majority of the population at one of the sites was nearly eliminated (with the exception of 2 plants) by slumping. 

The dependence of this species upon partially open areas may require special management. Human disturbance may reduce or increase the amount of habitat suitable for persistence or recolonization of this species. Periodic removal of woody vegetation may be necessary in order to maintain habitat in a suitably open condition. Although the species may be dependent on some form of disturbance for survival, not all disturbances are beneficial. More research is required to determine the impacts of management.