author: Alexis Riopel, August 29, 2020
translation: GoogleTranslate/doxa-louise
Bubbles form, others burst
“Bubbles isn't a concept we really use, but I can see the analogy. »Biologist Jacques Brisson runs a laboratory devoted to plant dynamics. The swelling (of populations), the implosion (of biodiversity) and the bubbling (of invasive species) are part of his daily considerations. And the metaphor of bubbles does not displease him.
“We can speak of a 'bubble' that was there before European colonization. The flora was in balance. With transport and travel, we brought a lot of plants from Europe, Asia and elsewhere, voluntarily or involuntarily, ”he says. These contributions have upset the relationships between native species, especially where the human imprint is deep, such as in southern Quebec.
When two bubbles merge, the shock is first brutal. Then a new balance can be created. Some species, like the daisy, integrate into their new environment and render useful ecological services. But sometimes the mixture is toxic. Specimens take advantage of this new domaine to inflate, inflate, inflate.
This is particularly the case of the common reed, also called phragmite, which is one of Mr. Brisson's favorite subjects. This herb detected in Quebec under its exotic shape for the first time at the beginning of XX th century, now colonizes agricultural ditches and edges of the province highway. Its stems, which can measure five meters in height, cover the ground so densely that all competition is crushed.
"It is the most widespread plant on the planet", points out the scientist, member of the Institute for Research in Plant Biology affiliated with the University of Montreal. We find native subspecies of common reed on all continents (except Antarctica), but some particularly virulent veins have jumped the oceans and invaded new horizons. Vessels releasing their ballast water likely introduced the problematic strain to North America.
Visit to the Boucherville Islands
Whoever wants to navigate in a mass of common reed must know how to make their way. “Long live the deer,” says biologist Kim Marineau, who accompanies Le Devoir in the tall grass of the Boucherville Islands to look for Phragmites. On this archipelago fifteen kilometers downstream from downtown Montreal, it is best to follow a corridor cleared by these deer to observe the conquering perennial from within its gains.
When we reach our destination, we see long, flat leaves stretching out all around us towards the sky. The soil, slightly sunken, must be very wet in the spring, our guide believes. “It starts like this, in a place where water collects,” she said. Then the colony can extend several meters per year, and possibly settle in dry environments. "
Biodiversité conseil, the company headed by Ms. Marineau, offers description services for natural environments, produces inventories of flora and fauna and draws up conservation plans. In addition, it fights invasive alien species, such as the common reed, and helps prevent its spread.
“In some places, we try to intervene,” explains the specialist. You have to dig four meters, remove all the soil that could contain roots, then install a geotextile canvas. A few years later, we remove the canvas and we can reforest. "
Before becoming a national park in 1984, the Boucherville Islands were used as agricultural land. However, says the biologist, not all the plots were immediately renaturalized: this left plenty of room for the reed to inflate its bubble. A single small piece of the plant, moved with the help of the archipelago's hydrographic network or road works, can give rise to a new colony.
Small bubbles
In addition to tackling the perverse effects of the bursting of ecological bubbles that once separated the continents, Ms. Marineau also tries to curb the fragmentation of habitats on a smaller scale. The objective here is the opposite: by connecting the isolated bubbles of nature, she hopes that the local fauna will be able to move as freely as possible on the territory.
"When we go below the 30% threshold of natural environments in a territory, ecological connectivity is degraded," she explains. All the species with large home ranges disappear, then slowly there is an erosion of biodiversity. "
Snakes and squirrels, for example, need green corridors to move from one bubble to another without risking falling prey to a predator. And even if the resources of their island can sometimes be sufficient to feed them in the short term, genetic exchanges with neighbors are essential in the long term.
In recent years, Ms. Marineau has contributed to the design of a large biodiversity corridor in the Borough of Saint-Laurent, in Montreal, the creation of which will take place over 20 years. She is currently working on a similar project in Rosemont – La Petite-Patrie.
While agricultural environments in the St. Lawrence Valley suffer from serious ecological connectivity problems, the problem does not spare more wooded regions either. The biologist gives the example of the southern Laurentians, between Saint-Jérôme and Mont-Tremblant Park: even if this area is over 80% covered with trees, there are essentially no more “interior forests”. »located more than 200 meters from a road, which makes it an unlivable environment for several animal species.
Arrangements are possible to limit the damage, but Ms. Marineau believes above all that urban sprawl must stop as soon as possible. “There cannot be infinite houses on a finite territory, in which we also want agriculture and natural environments accessible to humans. At some point, our quest is going to have to be different from that of the current model, ”she says.
The fragmentation of habitats is a problem all the more crucial as, in the coming decades, animal and plant populations will have to migrate little by little towards the north. “Normally, several species could not get out of their bubble or enter ours because of climatic constraints, underlines Jacques Brisson, but climate change is opening the way for new species. "
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