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Floodplains, risk areas

With a few exceptions, trees cannot survive long periods of submersion.
Credit: Space for Life (Daniel Sauvageau)
Forêt inondée
  • Forêt inondée
  • Forêt inondée
  • Grand héron et perchaude
  • Grenouille Léopard
  • Tortues peinte de l'est
  • Oies des neiges
  • Pair of wood ducks
Floodplains, risk areas

Rivers swollen by snow-melt that breach their banks every spring can cause enormous material damage to the homes built right next to them. This seasonal phenomenon is nevertheless part of a vital natural process for ecosystems of the St. Lawrence plain that I’d like to present to you here.

First of all, floodplains serve as buffer zones that make it possible to receive the runoff from rivers. They’re home to ecosystems that with their particular species are well adapted to these changing conditions and play an important role in the life of the river.

The most fascinating flooding-prone habitat in the St. Lawrence Valley is probably the silver maple forest (Acer saccharinum). The silver maple and the black ash adapt very well to flooding. Other species, however, are unable to survive long periods of submersion.

Silver maple forests are quite rare in Québec. The last beautiful ones can be found on the islands of the Lake Saint-Pierre archipelago.

Lake Saint-Pierre, a prolific nursery

Lake Saint-Pierre is a natural widening of the St. Lawrence River and not very deep (about three meters), located between the towns of Sorel-Tracy and Trois-Rivières. It’s the St. Lawrence River’s largest freshwater floodplain.

Its river marshes and its floodplain allow for the coexistence of very diverse examples of wildlife. A number of species of fish, like sturgeon and perch, lay their eggs in the flooded fields and woods, and the fry live there until the waters recede. The area also features, in early spring, the deafening din produced by the nuptial get-togethers of northern leopard frogs (Lithobates pipiens). Unhappily, many of these marshes have been transformed for growing corn and soya. That land is therefore no longer favorable for spawning, the breeding season for fish.

Recent research has identified Lake Saint-Pierre aquatic plant habitats as the primary spawning grounds for yellow perch (Perca flavescens). The considerable reduction of that habitat could well be the reason for the almost complete disappearance of the species, forcing the closure of a very important commercial fishery.

An important migratory stopover

Lake St-Pierre is regarded as the most important migratory stopover in eastern Canada for wild waterfowl. The flooded land offers a vast choice of habitats for different species of geese and ducks, who can comfortably await the thawing of the lakes and marshes of the Canadian Shield.

Although most of these birds continue their journey to the north in order to breed there, a number of them spend the summer at Lake St-Pierre, where they raise their young. The flooded forest of Grande Île is home to the largest heron colony in North America, amounting to 1,300 breeding pairs of great blue herons and black-crowned night herons.

Ecosystems at risk

The floodplains and other woodlands are essential ecosystems for the life of the St. Lawrence River as well as for migratory birds.

Property bordering the water may be highly attractive for the construction of homes or for agriculture, but this arrangement is detrimental to the ecosystem, which is now seriously threatened. It’s estimated that 70 percent of these wetlands, so important for maintaining a dynamic, healthy ecosystem, have disappeared over the last 50 years. Moreover, the belief is that this situation risks intensifying because of climate change.

This is therefore a habitat that’s essential to protect for our well-being and for that of our environment. Unfortunately, we’re possibly starting to pay the price of our lack of concern.

Reference:

“Le lac Saint-Pierre, un joyau à restaurer” (Lake St-Pierre: A Gem to be Restored), Government of Québec, 2013.

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