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COSEWIC Assessment and Status Report on the Eastern Flowering Dogwood in Canada

Technical Summary

Cornus florida L.

Eastern flowering dogwood
Cornouiller fleuri

Range of Occurrence in Canada: Carolinian Zone/ Deciduous Forest Region of extreme southern Ontario.


Extent and Area Information

Extent of occurrence (EO)(km2)
approximately the area of the Carolinian Zone
22 500 km2



Specify trend in EO

no significant change

Are there extreme fluctuations in EO?

No

Area of occupancy (AO) (km2)
(1 km2 per site;154 sites, 1975-2005)

about 150 km2



Specify trend in AO
(one site lost to development, several imprecise historical records not found)

no significant change



Are there extreme fluctuations in AO?

No

Number of known or inferred current locations

About 154 (66 1995-present plus 88, 11-30 yr. old records)

Specify trend in #

no change

Are there extreme fluctuations in number of locations?

No


Specify trend in area, extent or quality of habitat

Continuing minor decline of area and quality of habitat


Population Information

Generation time (average age of parents in the population)
10-30 years


Number of mature individuals
Based on estimated 7-8% per annum mortality in the last 3 years of diseased trees out of a total of about 1600 trees estimated as occurring at 154 sites recorded from 1975 to 2005 [about 660 from 57 recently observed sites, 940 estimated from others].

About 1200-1300








Total population trend:

steep decline

% decline over the last/next 10 years.
87% decline recorded over 11 years at two sites;
17% mean mortality (~3 years) observed in 32 sites

80%





Are there extreme fluctuations in number of mature individuals?

no, steady decline


Is the total population severely fragmented?

no


Specify trend in number of populations
Loss of populations imminent with trends in population sizes

only slight decline at this time



Are there extreme fluctuations in number of populations?

no

List populations with number of mature individuals in each: See Table 2 for detailed summary of 32 sites and 468 live trees. Similar details are not available for 122 sites except for total counts or estimates of numbers.


Threats (actual or imminent threats to populations or habitats)

Dogwood anthracnose is the major threat; first confirmed in Canada in 1998.
Habitat loss, degradation and fragmentation, slow decline as woodlots are cleared for agriculture or converted to housing.


Rescue Effect (immigration from an outside source)

Status of outside population(s)?
U.S.A.: this is where dogwood anthracnose disease was first recognized; populations are heavily impacted there.

Is immigration known or possible?

possible

Would immigrants be adapted to survive in Canada?

yes


Is there sufficient habitat for immigrants in Canada?

yes


Is rescue from outside populations likely?

No; infrequent dispersal of seeds from the south, but populations there also affected by dogwood anthracnose.


Quantitative Analysis


Current Status

COSEWIC: Endangered( 2007)
Ontario (NHIC): S2


Status and Reasons for Designation

Status: Endangered
Alpha-numeric code: A3e + A4ae; C1 + C2a(i)

Reasons for Designation: A small understory or forest-edge tree present only as small populations within the fragmented woodlots of southern Ontario’s Carolinian forest. The spread of dogwood anthracnose disease has caused dramatic declines in the Canadian populations that reflect similar declines throughout the species’ range in eastern North America. This assessment of risk applies only to wild populations and not to cultivated plants in nurseries, parks, and gardens.


Applicability of Criteria

Criterion A (Declining Total Population):
Meets Endangered A3e + A4ae since a population decline of >50% is projected over the next 3 generations (30-90 yrs) based on the impacts of a pathogen and as a consequence of having observed and projected a decline of >50% over 3 generations that includes the past and future.

Criterion B (Small Distribution, and Decline or Fluctuation):
Not met. Although the area of occupancy is under the threshold for endangered, the population is not considered to be severely fragmented in view of the ease of dispersal of fruit and seeds by birds and there are no extreme fluctuations in such factors as numbers of populations.

Criterion C (Small Total Population Size and Decline):
Meets Endangered C1 + C2a(i) based on population size estimated as <2500 trees and a significant continuing decline is projected due to the dogwood anthracnose disease with no population having >250 trees.

Criterion D (Very Small Population or Restricted Distribution):
Not met since numbers of trees exceed limits for Endangered and Threatened and the area of occupancy of the numerous sites exceeds 20 km2.

Criterion E (Quantitative Analysis):
None available.