Dwarf hackberry (Celtis tenuifolia) COSEWIC assessment and status report: chapter 2

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COSEWIC Executive Summary

Species Information

Dwarf hackberry (Celtis tenuifolia) is a small tree or shrub of the Elm family with stiff, often divaricately branched twigs and grey bark. Its leaves are variably toothed along the terminal part of the blade. Its globose, orange-brown fruit has a sweet outer layer and contains a single seed; the fruit often remains on the trees through the winter. Common hackberry (Celtis occidentalis) also occurs through much of its range in Ontario.

Distribution

It ranges from the lower Mississippi to the Atlantic piedmont, with its distribution becoming scattered in the north with about 20 disjunct populations in the lower Great Lakes region. Six of these isolated populations occur in southern Ontario.

Habitat

In Ontario it occurs on dry, calcareous soils, sand spits and dunes or areas of shallow limestone bedrock (alvars), in open woodlands.

Biology

Dwarf hackberry is a perennial woody plant. Flowers are unisexual, both on the same plant, self-compatible and wind-pollinated. The fruit is mostly bird-dispersed. It occurs on very dry sites. Three of the populations occur with common hackberry, and intermediates exist that suggest the possibility of hybridization between these two native species.

Population Sizes and Trends

Six populations are known in Ontario with about 893 reproductive individuals. Populations appear to have remained steady from previous counts 10 years ago, with the observed increase likely representing a better knowledge of this species’ distribution.

Limiting Factors and Threats

Bark beetles are known to cause a high level of mortality, 10% per year over two years was recorded in 1989-90. This past problem was not evident in the recent observations. The quarrying of limestone in areas of alvars in eastern Ontario and the potential of expanding sand extraction in another site are threats to the habitat of this species.

Special Significance of the Species

Dwarf hackberry occurs on sites of extreme drought and with a number of other rare species of plants. It is host to several rare insects, including beetles that have only recently been recognized in Canada. While not currently available in the landscape trade, it has potential for use in areas of extreme drought.

Existing Protection or Other Status Designations

It currently does not have protection under the Ontario Endangered Species Act, being listed only as Vulnerable there, and Special Concern in Canada.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species and include the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal organizations (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership, chaired by the Canadian Museum of Nature), three nonjurisdictional members and the co-chairs of the species specialist and the Aboriginal Traditional Knowledge subcommittees. The committee meets to consider status reports on candidate species.

Definitions (After May 2003

Species

Any indigenous species, subspecies, variety, or geographically defined population of wild fauna and flora.

Extinct (X)

A species that no longer exists.

Extirpated (XT)

A species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A species facing imminent extirpation or extinction.

Threatened (T)

A species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)^Footnotea

A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)^Footnoteb

A species that has been evaluated and found to be not at risk.

Data Deficient (DD)^Footnotec

A species for which there is insufficient scientific information to support status designation.