Drooping Trillium Recovery Strategy Executive Summary
This document provides a summary of the recovery strategy for the Drooping Trillium, which advises the ministry on ways to ensure healthy numbers of the species return to Ontario.
Prepared by Jarmo Jalava and John Ambrose
Drooping Trillium (Trillium flexipes) is a perennial herb in the lily family, with the core of its range in the eastern United States. There are only two known extant occurrences of Drooping Trillium in Canada, both in extreme southwestern Ontario. Five historic occurrences were extirpated between 1848 and 1950. Drooping Trillium was designated as endangered by the Committee on the Status of Endangered Wildlife In Canada (COSEWIC) in 1996 (reassessed in 2000 and 2009) and by the Committee on the Status of Species At Risk in Ontario (COSSARO) in 2008. These designations are due to a highly reduced number of occurrences which are limited by low seed set and lack of habitat for population expansion and which also are threatened by human activities. The species is listed as endangered under Ontario’s Endangered Species Act, 2007 and the federal Species at Risk Act.
Drooping Trillium grows in rich beech-maple, oak-hickory or mixed deciduous swamps and floodplain forests which are usually associated with watercourses. The presence of a watercourse may benefit the plant by creating and maintaining a slightly elevated floodplain terrace where soils are a well-drained combination of loam and sand favourable to the species. Forest canopy cover is important to maintain woodland ground flora and to reduce competition with invaders of forest openings, although some light penetration appears to increase plant vigour and population densities of this species.
The main threats to the Canadian populations of Drooping Trillium are considered to be habitat loss or degradation associated with incompatible forestry practices, recreational trail use, invasive species and alterations to soil hydrology. The potential threats of collecting for horticultural uses, diseases, pests, and herbivory by deer have also been noted.
The recovery goal is to establish and maintain a viable population of Drooping Trillium in its current and historic range in Ontario. This will involve population viability analyses to determine if, and the degree to which, extant populations need to be enhanced. Such analyses also will determine the number and size of additional populations that need to be established in the species' historical range in southern Ontario. The objectives to achieve this goal are to:
- protect and manage habitat to establish and maintain a viable population of Drooping Trillium in Ontario;
- determine abundance, extent, health and dynamics of Drooping Trillium populations in Ontario through inventory and regular monitoring;
- address key knowledge gaps relating to the species' biology, ecology, habitat and threats;
- promote awareness and stewardship of Drooping Trillium with land managers, private landowners, municipalities, horticultural organizations and other key stakeholders; and
- where it is ecologically and logistically feasible, reintroduce Drooping Trillium to historical or other ecologically suitable sites.
Due to the isolated nature of the extant populations, a strategic management and stewardship approach is recommended. This includes coordination and consultation with a variety of partners including private landowners and the St. Clair Region Conservation Authority.
Given that Drooping Trillium does not occupy all apparently suitable habitat at the extant sites, it is suggested that the area occupied by the plants, as well as adjacent habitat extensive enough to protect the hydrological regime allowing for potential dispersal and population expansion be prescribed as habitat in the regulation. It is recommended that the area prescribed as habitat in a regulation for Drooping Trillium be a composite area delineated by applying the following two criteria: (1) a distance of 120 m from the outer limits of the area occupied by Drooping Trillium in order to protect the hydrological regime, and (2) the full extent of the Ecological Land Classification (ELC) ecosite polygon within which a population occurs. As new information on the species' habitat requirements and site-specific characteristics (such as hydrology) become available, these attributes should be used to refine the habitat definition. It is also recommended that the habitat regulation for Drooping Trillium be flexible enough to include repatriation and/or introduction sites that are necessary or beneficial to recovery. Drooping Trillium is occasionally cultivated for horticulture. Horticultural populations should be excluded from the regulation.