Management Research and Recommendations for  Île Bouchard and Île Á l'Aigle

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Executive Summary

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Water Level 

Water levels are decreasing in the St. Lawrence River
Artificial regulation

In order to keep a minimum depth for boat traffic, upstream dams hoard floodwater. This limits the River’s fluctuations, so high water during a flood isn’t so high anymore.

Climate change

Interiors of continents are expected to receive less water, so there will be less water in the Great Lakes watershed that feeds the St. Lawrence River.

The Effects of this decrease include:
Reduction of wetlands
An increased chance of Invasions by Exotic species


Erosion and Deposition

Overland erosion is minimal
Wave action causes most of the erosion
Île à l’Aigle:
Island sheltered from shipping channel
Deposition outweighs erosion
Île Bouchard:
Exposed to wave action from shipping channel
Extensive erosion on south shore
 Affects of Erosion on the Islands
Erosion and deposition alter habitat and affect succession
Tall and dense plant species will grow on shores sheltered from wave action (Île à l’Aigle)
Short and sparse species will grow on shores exposed to wave action (Île Bouchard)

Ecological Succession

Wetland Succession
Water level fluctuations determine distribution and composition of vegetation communities
Lowering water levels may dampen fluctuations
Predicted succession over next 10 years in wet areas:
Growth of tall, tolerant grasses such as Phalaris arundinacea
Invasion of wooded wetland species into current herbaceous wetland


Dryland Succession
Recent grazing pressure restricted much of the vegetation to short herbaceous species
Grazing presently prohibited
Predicted succession over next 10 years in dry areas:
Growth of small wooded patches
Tall grassland vegetation


Invasive Species

Purple Loosestrife
Common Reed

Vulnerable Species

Invasive plant species may out-compete the preferred habitat of many of our vulnerable species

Many of the vulnerable species are affected in the same way by the trends

A decrease in water levels and erosion will cause a reduction in the habitat of many of the species on the islands

Maintenance of a mosaic of vegetation will benefit many of our species


Nelson’s sharp-tailed Sparrow, Ammodramus nelsoni

Short-eared owl, Asio flammeus

Sedge wren, Cistothorus platensis stellaris

Black-billed cuckoo, Coccyzus erythropthalmus

Least bittern, Ixobrychus exilis

Common tern, Sterna hirundo

Teal lovegrass, Eragrostis hypnoides





Monitor population health of vulnerable species

Monitor invasives and take control measures if necessary

Monitor environmental conditions – water levels, erosion, ecological succession

Allow flooding to continue unabated

Survey islands systematically and in detail

Study whether bank erosion is necessary to retain the biological characteristics of the reserve

 To graze or not to graze?

We need to maintain a mosaic habitat

Examine the impacts of light grazing on the biological community

Overgrazing could reduce biodiversity, but limited grazing may increase the amount of mosaic grasslands.


Managing ecosystems is a very complex issue

There is no ‘grand Scheme’ solution

To maintain the existing biological diversity, maintenance of current levels of habitat diversity is crucial

There are several management strategies NCC may choose to incorporate




Organizations Involved

The Nature Conservancy of Canada,
Mcgill School of the Environment,