American chestnut (Castanea dentata) COSEWIC assessment and status report: chapter 13

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Technical Summary

Castanea dentata

American chestnut

châtaignier d'Amérique

Range of Occurrence in Canada: southern Ontario

Extent and Area Information

Extent of occurrence (EO)( km² ) [calculation based on its occurrence in a little less than half of the 22 500 km ² Carolinian Zone]

11 000 km ²

Specify trend in EO

Stable

Are there extreme fluctuations in EO?

No

Area of occupancy (AO) (km ² [calculation based on an estimated  average of 10 hectares or 0.1 km ² per site])

12 km ²

Specify trend in AO

Decline

Are there extreme fluctuations in AO?

No

Number of known or inferred current locations

120

Specify trend in #

Probably declining. More sites known likely due to more intensive search effort.

Are there extreme fluctuations in number of locations?

No

Specify trend in area, extent or quality of habitat

Declining due to forest losses

Population Information

Generation time (average age of parents in the population)

Healthy trees can live for many decades. 20+ years to flowering but most large trees die

Number of mature individuals [based on the recent survey with 85 reproductive trees + 16 counted by the author and Draper, 2002]

Estimated at 120-150

Total population trend:

Probably declining

% decline over the last/next 10 years or 3 generations.

>>50% in last 90 years

Are there extreme fluctuations in number of mature individuals?

No

Is the total population severely fragmented?

Yes, many mature trees are isolated and thus do not reproduce (due to self-incompatibility)

Specify trend in number of populations

Uncertain but perhaps a slight decline.

Are there extreme fluctuations in number of populations?

No

List populations with number of mature individuals in each

101 documented individuals in 120 sites (not all populations have had complete counts)

Threats (actual or imminent threats to populations or habitats)

• chestnut blight fungus
• hybridization with Asian species of Castanea
• general habitat loss and fragmentation in the Carolinian Zone

Rescue Effect (immigration from an outside source)

Status of outside population(s)?

Canada: ex situ trees potentially stable;
USA: Natural populations in jeopardy

Is immigration known or possible?

Unlikely

Would immigrants be adapted to survive in Canada?

Transplants: yes, if from appropriate source areas

Is there sufficient habitat for immigrants in Canada?

Habitat is available for re-introductions

Is rescue from outside populations likely?

No

Quantitative Analysis

Not Applicable

Previous Status

Assessed by COSEWIC in 1987 as Threatened

Status and Reasons for Designation

Status: Endangered

Alpha-numeric code: A4ace; B2ab(ii,iii,iv,v); C2a(i); D1

Reasons for Designation: Once a dominant tree in well drained forests of the Eastern Deciduous Forest, this species was devastated by chestnut blight in the first part of the 20^th century. The species is still present throughout most of its former range, but as a few scattered individuals that have sprouted from root crowns. Most of these succumb to the blight before reaching a substantial size and fewer than 150 are large enough to produce seed. The species requires cross-pollination and seed set is reduced because mature individuals are widely scattered. Threats to the species include the continuous presence of the blight, aging and attrition of the root crowns, land clearing in some remaining sites, and hybridization with other species.

Applicability of Criteria

Criterion A (Declining Total Population):
Endangered under A4ace because there has been a well-documented decline of well over 50% in the number of mature trees within the last 70 years since chestnut blight spread across southern Ontario in the 1930s and 40s. Chestnut trees may reach fruiting condition in about 20 years, but usually succumb to blight as they reach maturity. Un-blighted trees lived for several hundred years. Seventy years thus represents fewer than 3 generations. Although American Chestnut occupies most of its former range, the AO has been reduced because the species now occurs as scattered individuals and some populations have been extirpated. Future losses will occur due to the deaths of root crowns.

Criterion B (Small Distribution, and Decline or Fluctuation):
Endangered due to limited distribution, fragmentation and decline under B2 (a)+(b, ii-v) with EO about 11 000 km² but an AO of about 12 km². Severely fragmented because only about 150 mature individuals are known and since the species is self-incompatible pollination is severely limited. Continuing decline anticipated in the AO and the number of locations as individual populations are extirpated and land clearing continues. The quality of forest habitat is declining in the Carolinian Zone from a number of causes (forest fragmentation, pollution, global warming, invasive species, pest and diseases). The number of mature individuals is projected to decline as individual rootstocks age and die and are not replaced from seed.

Criterion C (Small Total Population Size and Decline):
Endangered C2ai due to the small number of fruiting individuals (about 150) and very few mature individuals (<10) in any known population.

Criterion D (Very Small Population or Restricted Distribution):
Endangered under D1 due to the small number of mature individuals.

Criterion E (Quantitative Analysis):
Not applicable.