White wood aster (Eurybia divaricata) COSEWIC assessment and status report: chapter 11
SUMMARY OF STATUS REPORT
There are currently 15 extant populations of Eurybia divaricata in Ontario. Ten of 15 (66%) extant Ontario populations are small (< 100 plants) and/or at risk of destruction (Thompson 2000).
The population of Eurybia divaricata at Culp’s Woods is located in an isolated woodlot surrounded by peach orchards. This population is not likely to spread to surrounding woodlots due to its isolated position. In addition, it appears that the population has diminished greatly since 1991. This could be due to impacts from the orchard operations, or clearing of the woodlot for expansion of the orchard.
The populations at Four Mile Creek-Niagara Shores are just barely 1 km apart. They could be considered part of the same population, although it should be noted that the sub-populations within the Niagara Shores Conservation Area are at high risk of extirpation due to their location along the main trail system. The populations located within the Department of National Defense property contain more plants and are probably more protected, as gaining access to this property is difficult.
The populations at Short Hills Provincial Park are large and scattered. The author noted that poor health, erosion, and grazing by deer could be affecting the population at Twelve Mile Creek ANSI. At the Cataract Woods site, the population seems quite healthy and very large, despite the trail system.
The population at Marcy’s Woods appears stable, but is at risk due to the fact that a trail runs through its center, and that the land is privately owned and may be sold for development.
The population of Eurybia divaricata at the St. John’s Conservation Area is quite small and is in very poor condition. The trail on which the species is located is a spur trail and may not be highly used, but many of the plants were trampled. It is not likely that this population will be able to survive without immediate protection.
It is likely that Eurybia divaricata is present at the Nelson Quarries site, although it is probably not found in large numbers. It is not known whether this area is slated for quarry expansion. The presence of a rare community type (black maple (Acer nigrum)-chinquapin oak (Quercus muhlenbergii) in the immediate vicinity may lead to protection of the site. In addition, the globally rare (G2) Virginia mallow (Sida hermaphrodita) occurs at the site. If more inventory work is attempted at this property, the chances of relocating Eurybia divaricata will be good.
Lastly, the Fonthill-Sandhill Valley ANSI must be considered the most viable and stable population in Ontario. Eurybia divaricata is widespread within the ANSI. Although there is no formal protection for this area, it is unlikely that Eurybia divaricata could become extirpated from this site without a great deal of disturbance. More work should be done to assess the full extent of Eurybia divaricata within the ANSI. In addition, the private landowners should be informed of the presence of this species and protection afforded under the Ontario Provincial Policy Statement.
There are currently 10 reported populations of Eurybia divaricata in 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. It is highly recommended that surveys be completed for all reported locations of Eurybia divaricata in Quebec in order to clarify the status of the species in that province.
There are only 25 reported locations of Eurybia divaricata in Canada, many of which have not been monitored for several years. Of the populations that have been recently confirmed, all but two are threatened to some degree, either by habitat destruction and development, trampling, small population size or environmental factors such as competition with invasive species and deer browsing or weevil consumption. Many of the sites in Ontario are located on public lands and do have some protection through management, but the majority of Quebec populations are on private lands where they are at risk.
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