Dwarf hackberry (Celtis tenuifolia) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Populations were resurveyed in 2002 and compared with earlier records (Table 1). While there are some large populations, a high rate of turnover was observed at Point Pelee, with a10%/year mortality over two years, in 1989-90, due to mortality caused by bark beetles (Dunster, 1992). However, this may be a cyclical occurrence; significant levels of mortality were not observed in any population in 2002. Since the first status report of 1984, the Point Anne site has been confirmed and two additional sites in the nearby region have been documented.

Most of the numbers likely represent a steady population size, with some possible local increases. For example, Fish Point lost one large specimen along the west edge of vegetation due to lake action in the 1980s, maintained 4 mature individuals away from the lake and gained several new non-reproductive saplings. Point Pelee was more difficult to assess, with a dispersed population and insufficient time to re-inventory the entire 4+ km long site, however, numerous individuals were observed where surveyed. Monitoring of a few precisely located groups of individuals would give a better determination of trends. The Ipperwash to Pinery population is the largest in numbers and range and appears to be maintaining a steady size. The Pinery site was surveyed for only one day and included about a third to a half of the known area of this species. The Hastings County populations contain individuals that appear to be old in mature habitats, so these sites are likely recent discoveries of established populations rather than a recent expansion of the species. A local naturalist showed us one population and two field volunteers helped find the individuals in the three sites over two days, so the counts likely represent close to the full populations of those sites, though other regional alvars are possible sites of undocumented populations.

Table 1. Actual counts of Ontario populations of Celtis tenuifolia
# Location Population Klinkenberg, 1984 Dunster, 1992 Footnotea [+other] 2002
1a. Essex County Pelee Island, Red Cedar Savannah 1 -- Only C. occurrence found
1b. Essex County Pelee Island, Fish Point 5 -- 5+7+?; +Co/Ct?Footnoteb
2. Essex County Point Pelee National Park widespread and uncommon 136+48+715 33+5+2 in one area; +Co/Ct?Footnoteb
3a. Lambton County Ipperwash sporatic stands within 3 X 10 km area    
3b. Lambton County Port Franks/Northville sporatic stands within 3 X 10 km area 473 +781+1813 655+655+few
3c. Lambton County Pinery Provincial Park sporatic stands within 3 X 10 km area   34+25+150
4. Hastings County Point Anne -- [1st observation 1982, few trees] 2+0+5; + Co/Ct?Footnoteb 7+0+6
5. Hastings County Stirling Slope -- [1st observation 1991, 1-few (+1 outlier)] 23+2+few
6. Hastings County Lonsdale -- [1st observation 1993, 6 plants] 2+1+2; + Co/Ct?Footnoteb 4-1-1

For an estimate of the total Ontario population, see the Technical Summary [it is estimated that there may be about 35 trees at site 3b].

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