Management Plan


A good quantity of information on Grosse Île’s plant life has been available for some time now. This explains why conservation priorities have need developed primarily in relation to these resources. This analysis was conducted for the most part using the plant communities identified by Marineau (1995). Each community was examined according to the following criteria: diversity, sensitivity, degree of disturbance and uniqueness. These criteria were assessed for each community in the form of a rating designed to facilitate prioritization and enhance objectivity. Each of these criteria has been weighted according to its ecological importance. Criteria were defined as follows:


By the sensitivity of plant communities is meant the intrinsic fragility of each component and the representativeness (range and dispersion) of each community on the island. Sensitivity may be associated with: the presence of rare or endangered species; wetlands; thin, erosion-prone soil; plants located at the furthest limit of their distribution area; particular communities that are poorly represented on the island; etc. Sensitivity is the main determining criterion, setting off the vulnerability of plant communities in connection with disturbances in a given habitat. Certain plant resources or communities can be stressed by human activity to the point of being irreversibly damaged or destroyed, thus justifying the high value accorded to this criterion. The following ratings were established accordingly:

Very high : 12

High : 8

Medium : 4

Low : 0


The federal government is committed to preserving this country’s biodiversity. In addition, in its role as defender and promoter of our natural and cultural heritage, Parks Canada has pledged to protect species-rich habitats. That is why this criterion has been accorded practically the same importance as sensitivity. To evaluate this factor and define the appropriate qualitative rating, each community studied by Marineau (1995) was appraised with reference to the richness of species and the indexes of Simpson and Shannon. The following ratings were established accordingly:

Very high : 8

High : 5

Medium : 2

Low : 0

Degree of disturbance

Studying the degree of disturbance characterizing each plant community tends to indicate to what extent the current environment may be considered to be the result of natural evolution, given the major disturbance that has occurred in conjunction with human settlement of the island. Emphasis was placed on stresses occurring in the last several decades, the seriousness of these stresses and how permanent they appear to be. The weight of this criterion is less than that of the two preceding criteria. It nevertheless plays a key role because it serves to distinguish the most representative and the least disturbed sectors of plant communities on the island. The following ratings were established accordingly:

High : 0

Medium : 2

Low : 4


A number of plant communities may be considered “unique” on the island or in the region. They may stand out for any of the following reasons:

  • their intrinsic qualities as a landscape unit;
  • the presence of species of wildlife or vegetation that are either rare or endangered, poorly represented or presenting a scattered distribution;
  • their conservation in a natural habitat, or a habitat that has been only slightly disturbed by human settlement.

The following ratings were established accordingly:

Uniqueness : 4

Non-uniqueness : 0

The total of ratings for each Grosse Île plant community were used to establish conservation priorities for the site (see table) according to the following four categories:

Priority I : rating totals from 18 to 28, inclusively;

Priority II : rating totals from 13 to 17, inclusively;

Priority III : rating totals from 8 to 12, inclusively;

Priority IV : rating totals from 0 to 7.

It should be pointed out, however, that the above-described assessment was not applied to the plant communities located along the island shoreline. Given that most of the rare, threatened or endangered plants are distributed more or less in communities all along the shoreline, it is clear that this zone requires the highest degree of protection.

Appendix 2: Conservation priorities for Grosse Île natural resources

Natural resources evaluation criteria
Conservation priorities
Definition of categories of conservation priority