White wood aster (Eurybia divaricata) COSEWIC assessment and status report: chapter 7

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POPULATION SIZES AND TRENDS

Trends

Sharp et al. (1995) reported 8 populations in Canada, 3 in Ontario and 5 in Quebec in the previous status report.  Seven of 22 known Ontario sites (32%) are presumed extirpated (NHIC 2002).  Population numbers and population sizes (number of stems) within the populations in Ontario have increased since 1995.  This could be due to favourable environmental factors and an intensified search effort. 

In Quebec, there are currently 9 populations listed in the records of the Centre de données sur le patrimoine naturel (Gouvernement de Quebec, 2001).  There is also one population listed in the 1995 status report that is not listed in the Centre's records.  This makes a total of 10 possibly extant populations in Quebec.  There has therefore been a 50% increase in the number of reported locations in Quebec, yet populations have not been monitored consistently and it appears that the number of viable populations is low and may be decreasing.

Numbers represent total number of stems found at the site, both vegetative and flowering.  It is difficult to determine the number of clones represented in some of the populations without damaging the plants.  The use of the term "sub-populations" indicates separate populations (or separate clones) found at the same location.

Note: Subsequent to the completion of the draft update report for this species, new information became available indicating that, in Ontario, a historic site has been rediscovered and additional new sites had been found.  With this new information, the total number of records for the province was 22 with 15 of these extant.  The new population data were provided to COSEWIC members at the time of discussions and assessment of this species in November 2002 and were incorporated into this finalized copy of the report.

Table 1. OntarioPopulation Summary for Eurybia divaricata.

Summary of Extant Populations: Ontario

At one time, Eurybia divaricata was found at 16 sites in Ontario.  The 1995 status report (Sharp et al., 1995) reported 3 sites for Ontario.  8 sites in Ontario were extant as of the year 2000.  New fieldwork in 2002 has led to the discovery of 7 new sites, resulting in a total of 15 sites in Ontario.

Crescent Estates Woodlot

This site lies along a small creek and is bounded by successional meadow and residential development. The creek has been channelized in preparation for further urban development (Brady 1980).  Vegetation consists of deciduous trees such as hawthorn, white elm, black oak, white ash, red oak, and shagbark hickory (Santarella 1986).  Ken Ursic found 100 plants in this area in 2002.  The areas in which Eurybia divaricata have been found have been described as pin oak deciduous swamp and red maple mineral deciduous swamp.  Intentional harvesting or coincidental shallow excavation was observed in 2002 (Ken Ursic, pers. comm.)  This area is privately owned. 

Culp’s Woods

The Culp’s Woods site is a remnant American beech-sugar maple-white ash woods.  The moisture regime within the forest is mesic to dry-mesic and the soils are loamy clay (Sharp et al., 1995).  In 1991, the population consisted of thousands of individuals. The population of Eurybia divaricata has declined since 1991, and consists of approximately 400 individuals.  Parts of this woodlot have been cleared and used as a peach orchard since 1991, resulting in a decrease in the numbers of individual plants at this site.

DufferinIsland

Vegetation at Dufferin Island is mainly sugar maple, white ash and white elm, as well as willow and staghorn sumac.  Helen Macdonald found 15-20 plants in 2002.  Plants were located along a path at the base of an oak tree.  This area is owned by the Niagara Parks Commission.

Fonthill-Sandhill Valley ANSI

At this site, areas where Eurybia divaricata has been found are noted as upland (ridge, slope and terrace) forests with a soil texture of sand to clay and a wet-mesic to dry moisture regime (Kaiser, 1986).  Eurybia divaricata appears to be widespread throughout the ANSI, with higher numbers on the drier ridges.  It is estimated that there are thousands of plants within the ANSI.  It is likely that this is the largest and most stable population in Ontario, due to its widespread distribution and abundance.

Marcy’s Woods (Point Abino Peninsula ANSI)

The upland forest communities of Marcy’s Woods are dominated by sugar maple and red oak, occurring primarily on sand dune ridges (Oldham, 2000). The author counted approximately 200 plants in this area in 2001.

Miller Creek Swamp Woodlot

Ken Ursic found 100 plants at this location in 2002.  Eurybia divaricata was found on an upland fresh-moist sugar maple-hardwood section in this deciduous swamp forest.  This area is privately owned.

Nelson Quarries

An ecological inventory submitted by Dougan and Associates in 1999 indicated that Eurybia divaricata was discovered and collected within an area adjacent to a property owned by Nelson Aggregates (Dougan and Associates, 1999).  The area in which Eurybia divaricata was discovered is considered dry to fresh Sugar Maple-Oak upland deciduous forest.  The author searched this site and could not locate any Eurybia divaricata.  It may be that this site is extant, and further searching may lead to the rediscovery of this population.  This population may be at risk from development, as it is surrounded by active quarries.  In addition, there are several logging roads running through the property and it is unknown whether logging activities are continuing within this woodlot.

ShortHills Provincial Park

Sections of Short Hills Provincial Park that contain Eurybia divaricata are composed of upland sugar maple forest, with dry mesic to mesic silty clay soil (Sharp et al., 1995).  In 2002, a thorough examination of the park has increased the number of stems found to approximately 5350. 

Cataract Woods

Less than 100 plants were recorded from this area in 1988.  In 1995 and 1999 surveys indicated that there were 300-400 plants in this area.  In 2000, there were approximately 1300-1400 plants in total within this area.  In 2002, this number had increased to 3800 stems. 

Twelve-Mile Creek ANSI

Although the majority of the plants in the park appear to be healthy, in some areas the plants appear to be suffering.  Although there were between 350 and 400 plants present in the Twelve Mile Creek area in 2000, the majority of the plants were <15 cm high and were not flowering.  This could be due to an increase in the density of the canopy. Eurybia divaricata populations in some areas had been grazed, possibly by deer, which seem to be abundant in this part of the park.  By 2002, the number of plants in this subpopulation had decreased to 25.  The total number of plants in this area has increased due to increased search effort.  Approximately 1555 plants are scattered in the area. 

South Fort Erie

This area has been described as a fresh-moist oak-maple deciduous forest.  Ken Ursic found 20 to 30 plants at this location in 2002.  This woodlot is slated for a draft plan approved subdivision.  The site is privately owned.

South Fort Erie2

This population is located adjacent to a road.  Ken Ursic found 3 plants at this location in 2002.  This woodlot has been described as a dry fresh sugar maple oak deciduous forest.  This area is privately owned.

St. JohnsConservation Area

St. Johns Conservation Area also supports a population of Eurybia divaricata.  American beech (Fagus grandifolia) forms most of the canopy in this woodland, with white oak (Quercus alba), sugar maple (Acer saccharum) and Carolinian affiliates.  In 2000, this population consisted of 18 individuals.  The population was trampled, although many of the stems were in flower.  A stem count of this population in 2002 found that the number of plants had been reduced to three very trampled stems.  The Niagara Peninsula Conservation Authority is aware of the perilous situation of this population and has taken measures to ensure the protection of the plants at this site.

Summer Street Woodlot

This area has been described as fresh-moist sugar maple-hardwood deciduous forest.  Ken Ursic found 20 plants at this location in 2002.  The canopy vegetation is dominated by Black, Red, Silver and Sugar Maple, American Beech, Red, White, Pin and Swamp White Oak, Basswood, Red and White Ash, White Elm, Shagbark Hickory, and Black Cherry.  The terrain is flat, moderately well drained, and not as wet as nearby areas.  The area is bordered by cultivated fields and successional meadow (Brady 1980).  This area is privately owned.

Two Mile - Four Mile Creek Area of Natural and Scientific Interest 

NiagaraShoresConservation Area

The Niagara Shores Conservation Area population is located on a forested barrier beach dune between Lake Ontario and Four Mile Creek.  Two sub-populations of Eurybia divaricata are located on a well-drained, wooded sand beach ridge consisting of silt loam to loam to fine sandy loam (Sharp et al., 1995).  A total of 25 plants were found by the author in 2000.   In 2002, this population had increased to 165 plants.

Department of National Defense

A population was also located on the Department of National Defense property.  This consisted of 3 sub-populations totaling 165 plants, all within a 1 km² area.  A second colony of plants reported from this area has not been located since 1991.

A more detailed account of the extent of Eurybia divaricata in Ontario can be found in the COSSARO status report (Thompson, 2000).

Summary of Extant Populations:Quebec 

The 1995 status report for Eurybia divaricata reported 5 stations in Quebec.  There are currently 9 locations listed in the database of the Quebec Centre de donnees sur le patrimoine naturel.  Together, these two sources have listed a total of 10 sites for

Quebec.  Since many of the sites have not been monitored or confirmed in several years, it is difficult to determine how many of these sites are still extant.

Table 2.  Quebec Population Summary for Eurybia divaricata

Venise-en-Quebec

This colony consisting of 2-3 colonies of Eurybia divaricata was located under a canopy of white pine (Pinus strobus), hickory (Carya spp.), red oak (Quercus rubra) and balsam fir (Abies balsamifera).  Another colony located in the same area was found growing in the shade of eastern hemlock (Tsuga canadensis) with yellow birch (Betula alleghaniensis) (Sharp et al., 1995).  This area is privately owned and has been developed as a golf course.  A population of clones was recorded alongside the ditch close to the golf course.  This population has not been confirmed since 1985 (Gouvernement du Quebec, 2001).

Philipsburg Migratory Bird Refuge

Two colonies of Eurybia divaricata were located at this station in 1987.  One population was found growing on the side of a small hill underneath eastern hemlock.  A second population was found growing in an understory of sugar maple (Sharp et. al., 1995).  This population is not listed in the occurrences for the Quebec Centre de données sur le patrimoine naturel and the status of this population is unknown.

MontSt-Gregoire

This station is located in a large wood with an understory of American beech. One clone consisting of 15 stems was reported.  American ginseng (Panax quinquefolius) and putty-root (Aplectrum hyemale) were found nearby.  This property was under development pressure by the landowner when it was last seen in 1987.  The landowner had been using the area as a landfill.  It is unknown whether this population is still extant (Gouvernement du Quebec, 2001).

Colline Spruce 

Eurybia divaricata was located in a rocky sugar maple-beech forest (about 50 years old) that has undergone partial cutting.  Plants were located on a small hill, with hobblebush (Viburnum lantanoides), round-leaved violet (Viola rotundifolia), wild sarsaparilla (Aralia nudicaulis), alternate-leaved dogwood (Cornus alternifolia), mountain maple (Acer spicatum), silvery glade fern (Deparia acrostichoides), New York fern (Thelypteris noveboracensis) and panicled hawkweed (Hieracium paniculatum).  A single plant in flower was located (third week of September, 1992) in a search area of 150 by 300 m.  It is not reported whether there were vegetative stems present at this site (Gouvernement du Quebec, 2001). 

MontPinacle 

Eurybia divaricata was found in a rocky sugar maple and ash dominated woodlot (about 50 years old) that has undergone partial cutting.  Five or six individual plants in flower (4-7 flowers on each plant, first week of September in 1992) and a dozen vegetative rosettes, all of less than 40 cm in height, were located in an area of 20 by 50 m, principally on the third level of the escarpment (Gouvernement du Quebec, 2001).

MontRougement 

Eurybia divaricata was recorded on a dry and rocky slope in a sugar maple-beech forest at this location.  2 colonies were found, adding up to approximately 1000 individuals. 50% of the individuals were in full flower the first week of September in 1998 (Gouvernement du Quebec, 2001). 

Saint-Armand

The population of Eurybia divaricata located at this site was found with an understory of sugar maple and hemlock, with bulblet fern (Cystopteris bulbifera) and white snakeroot (Eupatorium rugosum).  Two isolated clones were found at this location, flowering the fourth week of August and the fourth week of September in 1996 (Gouvernement du Quebec, 2001).  An estimate of the number of stems was not provided. 

Frelighsburg 

Petit Pinacle  

Eurybia divaricata was located on the low end of the slope of a rocky hill bordering the bank of an intermittent stream.  The forest in this area is dominated by sugar maple, yellow birch, hop hornbeam (Ostrya virginiana) and eastern hemlock.  Approximately 800 plants in two sub-populations (700 and 100) were recorded, covering an area of about 30 metres square.  Plants were observed in full flower and were beginning to fruit the third and fourth weeks of September in 1994 (Gouvernement du Quebec, 2001).

Saint-Armand Centre  

Eurybia divaricata was located on two hills situated along a rocky talus, under cover of sugar maple, bitternut hickory (Carya cordiformis), yellow birch and hop hornbeam associated with white snakeroot.  Two colonies totaling more or less 100 stems in an area 25 meters/square were located in 1997 (Gouvernement du Quebec, 2001).  

St. Blaise

At this site, Eurybia divaricata was located in a sugar maple forest with associates of bitternut hickory, black walnut (Juglans cinerea) and large-toothed aspen (Populus grandidentata).  Understory is dominated by zigzag goldenrod (Solidago flexicaulis).  A single clone in an area of about 3 metres square was found at the summit of a small hill.  This population was last observed in September 1997 (Gouvernement du Quebec, 2001).