White wood aster (Eurybia divaricata) COSEWIC assessment and status report: chapter 5

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HABITAT

Habitat requirements

Eurybia divaricata is a plant of open, dry deciduous forests. All Ontario stations occur within the Niagara section of the deciduous forest region (Rowe, 1972). These forests are dominated by sugar maple and American beech, but contain red, white and black oaks, shagbark hickory, basswood and Carolinian affiliates.  This plant requires well-drained soils, although it seems to do well in wetter years (such as 2000).  It may be suggested that this plant also likes some disturbance, as it seems to grow along trails in the majority of the populations in Ontario.

Populations of Eurybia divaricata in the Niagara region occur within the Niagara Fruit Belt and Lake Erie Counties climatic regions of southern Ontario.  This is one of the warmest regions in southern Ontario, with the longest growing season.  The Ontario sites are also in the Humid High Moderate Temperate Ecoclimatic Region of the Moderate Temperate Ecoclimatic Province (Ecoregions Working Group, 1989).  This ecoclimatic region is characterized by humid warm to hot summers and mild snowy winters.  Mean daily temperatures are above zero degrees Celsius from April through November.  Monthly precipitation is usually greater than 70 mm and is distributed fairly evenly throughout the year.

Quebec populations tend to occur in maple-beech forests with associates of bitternut hickory and hop hornbeam.  All populations are on well-drained soils or on the slopes of rocky hills.  Many of the woodlots in which this species occurs have been disturbed by some small-scale logging, which may have opened the canopy and allowed the populations to flourish.

The Quebec sites fall within the Humid Mid-Cool Temperate Ecoclimatic Region of the Cool Temperate Ecoclimatic Province.  These populations are at the northern limit of the species range.  This region is characterized by warm summers and mild winters with mean daily temperatures above zero degrees Celsius from April through November.  Monthly precipitation is usually greater than 75 mm (Ecoregions working Group, 1989).

Singleton 2001 found that Eurybia divaricata is very rarely found in postagricultural forests.  In addition, Singleton found that stem density of Eurybia divaricata declined with distance from old woods (Singleton et al, 2001).

Protection/ownership

Since the designation of Eurybia divaricata as a COSEWIC Threatened species in 1995, no steps have been taken to ensure the survival of this species in Ontario.  Two of the populations are located within a Provincial Park, two are located within Conservation Areas, and one is located on the property of a public parks commission.  All other populations are located on private property, though two are located within provincial ANSI’s (privately owned).

In Quebec, all of the populations are located on private property except for the Philipsburg population which is located at a migratory bird sanctuary owned by the Province of Québec Society for the Protection of Birds.