Swamp rose-mallow (Hibiscus moscheutos) COSEWIC assessment and status report: chapter 11

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Technical Summary

Hibiscus moscheutos

Swamp Rose-mallow – Ketmie des marais

Extent and Area Information

Population Information

Threats (actual or imminent threats to populations or habitats)

1. Habitat degradation
2. Shoreline development
3. Competition from invasive species

Rescue Effect (immigration from an outside source)

Quantitative Analysis

N/A

Current Status

COSEWIC: Special Concern (1987, 2004)

Sources of information: Fieldwork conducted in 2002 and slightly updated with Aug.- Sept. 2003 field data from A. Woodliffe.

• The Extent of Occurrence was calculated for the Ontario stations by joining, using GIS, the centroids of the outermost stations, i.e. Walpole Island, Sandbanks, and Main Duck Island, and subtracting the open water of Lakes Ontario and Erie captured within the polygon.
• The Area of Occupancy was calculated for the stations at Willowood West and St. Lukes Marsh by using a dot grid overlaid on a copy of 1998 infrared photos of the sites, knowing the approximate extent of the Hibiscus from the 2002 site inspections.  For the remainder of the 50 extant stations, the Area of Occurrence was estimated individually for each population, from the site inspections by the senior author in 2002 and from the information available from other observers.

Status and Reasons for Designation

Status:  Special Concern

Alpha-numeric code:   Met criterion for Threatened, D2, but designated Special Concern because it is relatively widespread, found in protected areas, and there is potential for rescue effect.

Reasons for Designation: A robust, perennial herb of shoreline marshes of the Great Lakes present in Ontario at many localities, in very small areas, and generally in low numbers.  The total Canadian population is estimated to consist of fewer than 10,000 plants with some, including two of the largest populations, in protected sites. The species has been subjected historically to habitat loss and several populations have been lost recently. Populations are also at risk from habitat degradation and impact due especially to invasive exotic plants. Evidence of the spread of plants through rafting of floating clumps indicates that rrecolonization of extirpated sites may be possible.

Applicability of Criteria

Criterion A (Declining Total Population: Not met (Insufficient information)

Criterion B (Small Distribution, and Decline or Fluctuation): Not met. The species has a relatively small area of occupancy (<10 km²), is present at many sites, but these are not deemed to be highly fragmented due to the floating seeds and rafting of uprooted plants; no extreme fluctuations occur in population sizes.)

Criterion C (Small Total Population Size and Decline):  Not met. Population size is estimated to consist of < 10,000 plants, meeting the threshold for threatened and continuing decline in mature individuals is suspected due to the spread of invasive exotics but no firm data has been documented and at least two populations have > 1,000 plants.)

Criterion D (Very Small Population or Restricted Distribution): Meets Threatened D2 based on the small area of occupancy and the continued shoreline development at many sites and the rapid expansion and impact of an exotic grass that has had great and increasing impacts in wetlands. Both factors have resulted in recent losses to entire or partial populations. Special Concern is recommended, however, due to the presence of many localities in a series of provincially and federally protected sites such as parks, conservation areas and provincially significant wetlands (including two of the largest populations). Rescue is also possible due to the spread of floating seeds and rafting plants.

Criterion E (Quantitative Analysis): No quantitative analysis available.