American chestnut (Castanea dentata) COSEWIC assessment and status report: chapter 9

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Population Sizes and Trends

The extent of the distribution does not seem to have changed significantly since the earliest records of 1817 (Moss & Hosking, 1983), even though numbers have been drastically reduced (likely greatly exceeding 50%) from when this species was a dominant species in some areas of southern Ontario (e.g., Duncan, 1993; Morley, 2001). It is and was widespread throughout the Carolinian Zone but more predominant in some townships, such as in portions of Norfolk County and around Hamilton where the species was noted to be most abundant in the 1817 survey (Moss & Hosking, 1983). Duncan (1993) indicates that in the Dundas Valley, in the Hamilton area, American chestnut made up 25 or 30% of the forest. Potential habitat does exist in southern Ontario, but it is limited due to the high level of forest clearing.

Three surveys were conducted between the 1980s and 2001-02. In the most recent survey, selected populations were intensively documented, following a strategy of the American chestnut recovery plan (Boland et al., 2000). The occurrence of reproductive trees and blighted trees is compared in the appendix from the data of the original status report (Ambrose & Aboud, 1986), a survey in the 1990s (Boland et al., 1997) and the recent inventory (Tindall et al., 2004). Data were compiled and analyzed by Brian Husband. Although there are statistically significant differences in reproductive status and the occurrence of blight symptoms among the three surveys in some of the age classes, the different approaches to the three surveys may in part explain the differences, viz., the first survey’s focus was on reproductive trees, the second, chestnut blight and its level of occurrence and virulence, and the third, a general assessment of the status of American chestnut (but dead trees were not recorded). Thus it is inconclusive whether the status of this species has significantly changed since the early 1980s although several large trees have been lost. It should also be noted that the devastation of this species is still within the time frame of a single generation of healthy trees.

In the most recent survey of 2001-2002, 682 individuals of all sizes were inventoried in detail, 85 of them were observed to be reproductive (individuals may have multiple trunks; counts are of individuals not trunks). An additional 13 trees of potential reproductive size and 7 smaller individuals were observed by the author in 2003. Some of these were in previously known sites, but four new sites were found while inventorying 24 county forests (total 1306 acres) in an unrelated project in Norfolk County (Ambrose & Waldron, 2004). Another survey was recently conducted in 16 Long Point Region Conservation Authority forests (Draper, 2002). Of these, chestnut was recorded in 10 forests, 7 being new sites, but with only three trees over 8.5 cm diameter at breast height. This gives an idea of the number of undocumented populations in a core area such as Norfolk County. Nevertheless, we may be losing important individuals as large trees die and do not re-sprout, and many of the small sprouts that eventually die out; there is a continuing concern over the loss of genetic diversity until the blight can be brought under control. In summary, 101 trees of potentially reproductive size are known in 120 sites; it is estimated that there are 120-150 reproductive trees plus 1000 or more smaller, non-reproductive individuals in Ontario. A comparison of sites with information from the first and last inventories is shown in Table 1. This table only includes those sites where a direct comparison can be made over this time period. For an additional estimation of trends, the appendix should be consulted.

Second line notes (2000s): Cinv: 2001-02 chestnut inventory, numbers only, size and other data not available at this time. Month 03: observations by author or others as noted.

The loss of several large trees documented in Table 1 that were reproductive and healthy in the early 1980s is a concern; whether they are being replaced by recruitment is inconclusive. For an analysis of all the data from the tree surveys, see the appendix.