Van brunt’s jacob’s-ladder (Polemonium vanbruntiae) COSEWIC assessment and status report: chapter 7

Population Sizes and Trends

The number of mature individuals of Polemonium vanbruntiae currently known in Canada is estimated at approximately 20,000, all in Quebec. In 2001, two new populations and two new subpopulations were discovered in Quebec, but this does not mean that the species is actually colonizing new sites, since these sites had never been explored. The density of populations varies from 1 to 20 individuals per square metre, based on our personal observations; the stricter density calculations made in 2001 can explain estimated population differences with the 1992 report, especially at Développement-Boisvert-Est. Accepting that the new populations recently discovered were always present but simply missed in previous surveys, there has been a slight decline in the overall population size due to recent losses of populations and declines at three.

Declines in the extent of occurrence and area of occupancy are primarily of historic occurrence. Recent discoveries are essentially of populations that were previously not documented.  On the positive side, agriculture has been declining in certain regions, such as the upper Nicolet River Valley, and some wet fields have been abandoned only to be invaded by Van Brunt’s Jacob’s-ladder.

Certain locations may undergo cyclical changes in the number of plants, especially those that have a lot of plants growing on abandoned farm land. These locations will likely face progressive invasion by trees, unless farming activities are resumed. This is the case at the Développement-Boisvert-Est, Saint-Camille and Stoke River locations, where about three quarters of the plants are found.

The species has probably always been rare in Canada, given the scarcity of its specialized habitats within its narrow Canadian range. If such a conspicuous plant had occurred in other regions, it would not have gone unnoticed. Data for calculating the overall decline in populations are inadequate. However, the number of plants has definitely declined over the past ten years at the Saints-Martyrs and Stoke River locations. This decline can roughly be estimated as a loss of 500 to 1,000 plants, but these figures are very approximate and are not based on systematic field surveys. It is possible that this decline is continuing, but efforts to acquire sites or negotiate conservation agreements with owners could slow down or even halt the decline.

The total Canadian population of Polemonium vanbruntiae is made up of a few small populations and a few large ones, but these are located in 4 distinct watersheds, those of the Nicolet, Nicolet-Nord-Est, Nicolet-Centre, and Stoke Rivers.

The estimated size and quality rating of the currently known Canadian locations (all in Quebec) are given below. Quality rating criteria are given in Table 1.
Locations Number of mature plants Quality rating
Saints-Martyrs
900
C
Développement-Boisvert-Est
13,000
A
Développement-Boisvert-Ouest
330
C
Saint-Adrien
1
D
Saint-Camille
2,000
C
Ham-Sud
300
C
Stoke River
3,000
C
Mont-Carrier-Sud
70
D
Table 1.  CriteriaFootnotea used to rate the quality of the occurrences (locations) of Polemonium vanbruntiae
Rating Desription
A population of over 10,000 individuals in a habitat that is little or not disturbed by human activities and that is stable over the long term.
B population of 1,000 to 10,000 individuals in a habitat that is little or not disturbed by human activities and that is stable over the long term.
C population of 100 or more, and fewer than 1,000 individuals, in a habitat that may or may not be disturbed by human activities, or population of more than 1,000 individuals in a habitat highly disturbed by human activities (agriculture, logging) and not stable over the long term.
D population of fewer than 100 individuals, in a habitat that may or may not be disturbed by human activities, or population of fewer than 1,000 individuals in a habitat highly disturbed by human activities (agriculture, logging) and not stable over the long term.

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