Houghton's goldenrod (Solidago houghtonii) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

Field visits were conducted at seven of thirteen sites for Houghton’s goldenrod reported in the NHIC database (Appendix 1). Sites were visited from August 18 to 20, 2003, comprising two and a half field days. Five sites were relatively inaccessible by road and could not be searched due to time constraints. One site was believed to be an erroneous report, since it was described as being on the north shore of Macgregor Point (which appears to be unsuitable habitat), and the UTM provided is in the waters of Frazer Bay.

Houghton’s goldenrod was found at five of the seven sites searched. Where plants were too numerous to count, population estimates were made by counting the number of plants in a transect one metre wide in order to establish plant density in , and then multiplying this amount by the estimated area of the patch in m² (area of occupancy).

One additional site was found near the swing bridge between the La Cloche Peninsula and Great La Cloche Island (Appendix 1). Pam Laureto, who was also conducting field survey’s in late August, 2003, reported three additional sites: one on the tip of White Point near the site reported by Morton in 1976, one on the south end of La Cloche Peninsula, and one at Stoney Point (Appendix 1). There are likely to be other occurrences in the La Cloche area. Laureto also provided a population estimate for the Strawberry Island site (pers. comm.).

Combining population estimates from the field visits with estimates from Laureto and those already reported in the NHIC database, there are approximately 27,000 mature flowering individuals of Houghton’s goldenrod in Canada. Area of occupancy is estimated to be approximately 7.4 ha, based on a density of 3,660 plants per hectare that was calculated from observed field data.

A comparison between observed numbers with previously reported numbers showed that while some sites experienced a decline, others experienced an increase. Overall numbers appear to be stable. Apparent declines and increases might also result if the observed site was not exactly the same one as previously reported, especially if location descriptions were vague.  Matthews and Mosely (1990) state that 20% of historically known populations globally have disappeared since 1975, but how much of this decline has taken place in Canada is uncertain.

There is some degree of isolation between populations, particularly Cabot Head, Cockburn Island, and to a lesser extent, Tamarack Bay.

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