Prepared by Judith Jones

Slender Bush-clover (Lespedeza virginica) is listed as endangered under Ontario’s Endangered Species Act, 2007 and on Schedule 1 of the federal Species at Risk Act. It is a perennial herb in the Pea Family with pink flowers and many narrow leaves crowded on upright stems. The seeds can remain viable for decades and can pass unharmed through the gut of an animal.

In Canada, Slender Bush-clover is present only in Ojibway Park and possibly at Tallgrass Heritage Park and Black Oak Heritage Park, all part of the Ojibway Prairie Complex in the City of Windsor, Ontario. Collectively, these three sites comprise a single population. The species has not been seen at Tallgrass Park since 1997 or at Black Oak Park since 1993. It is unknown whether the seed bank is still viable at these locations. Plants growing above ground were seen at Ojibway Park in 2011.

In Ontario, Slender Bush-clover is extremely limited by a lack of suitable habitat. In this province, the species is restricted to dry-mesic tallgrass prairie relicts with patches of exposed sandy soil. It requires full sun and open ground and does not tolerate dense shade or competition from surrounding vegetation. Some type of disturbance is needed to create open soil. Historically, this was probably fire or periodic drought. Existing habitat is highly fragmented into small patches that are isolated from one another by distances of hundreds of metres or more. Disturbance factors are also needed to disrupt the seed coat to improve germination.

Slender Bush-clover may be limited by some aspects of its reproductive biology. First, the relatively short growing season in Ontario might cause lower seed productivity than is found in populations in the southern part of the species' range. Second, factors responsible for breaking seed dormancy (such as fire, abrasion by sand, ingestion by herbivores) might be lacking at extant sites. Finally, the small, isolated Canadian population of Slender Bush-clover is at risk of being destroyed by a single stochastic event, such as a flood or wind storm.

The most serious threat to Slender Bush-clover is alteration of the natural disturbance regime (e.g., suppression of natural wildfire), which allows natural succession to proceed, resulting in habitat degradation or loss. Invasive species are another threat in need of urgent attention. All-terrain vehicle and dirt bike use are no longer threats.

The recovery goal is to maintain the abundance and distribution of growing plants of Slender Bush-clover at Ojibway Park at current or greater levels by reducing threats, and if the species is extant in the seed bank at the other two subpopulations, to increase the number of growing plants present there to pre-1995 levels. The protection and recovery objectives are to:

  • maintain or improve habitat suitability at the three existing sites;
  • reduce presence of invasive species at the three existing sites;
  • fill knowledge gaps; and
  • increase population size and extent if deemed feasible.

It is recommended that a habitat regulation cover all three Windsor sites and that at Ojibway Park the entire opening where the species occurs plus a protective zone of 50 m around the outside of the opening be prescribed. A definition of "opening" is given in the body of the text. At Tallgrass and Black Oak Heritage Parks it is recommended that a 50 m zone around the former area of live plants be prescribed as habitat to protect the seed bank and allow disturbance to occur even though live plants have not been seen in recent years. It is recommended that the Tallgrass and Black Oak sites be prescribed for 50 years unless live, growing plants of Slender Bush-clover re-emerge in which case habitat would remain prescribed beyond this time. It is recommended that restoration populations be regulated if they are planted within the three parks where the species is endangered and in natural vegetation but not in garden beds.