Combating invasive plants

The Jardin botanique de Montréal is known around the world for the expertise of its researchers in phytotechnologies, the science that uses plants to solve environmental problems. Over the past few years, the Jardin botanique has had the idea of setting up phytotechnology stations, a series of stations that allows us both to solve a problem we’re dealing with but at the same time turn it into an education and demonstration element to explain the operation and scope of the phytotechnological solution used. In 2019 the Jardin botanique inaugurated a first station that treats the water from the Aquatic Garden. In 2021 we raised the veil on a second station. This time the Jardin turned its attention to the problem of invasive plants in the area next to the Frédéric Back Tree Pavilion. Over the years, the small pond designed to lend a touch of freshness and beauty to this particular spot was invaded by unwanted plants, especially the common reed (Phragmites australis). Combating invasive plants that are already well established is a highly complex challenge, all the more so when the struggle has to take place in an aquatic environment. It was for this reason that the Jardin botanique opted for a more radical solution: restoring the environment completely and making it an exemplary project in controlling invasive plants.

Thus, construction of this new pond incorporated a number of elements that are useful for restricting the intrusion of invasive plants.

Native plants as a barrier to invasive plant life

The presence of an area densely occupied by native plants all around the pond constitutes the first barrier to the establishments of invasive plant life. That area brings not only a rich plant diversity that leaves little room for unwanted plants, but also acts as a biofilter that limits the leaching of nutrients caused by rainwater runoff. Elsewhere, shrubs that may provide the pond with shade were introduced. The effect of that is to maintain the coolness of the water and to impede the establishment of plants, like our famous common read, that need light to propagate.

Little green islands or, if you prefer, mattresses made from plants, were also installed. That original phytotechnology makes it possible to add filtering elements that move around the pond wherever the wind blows them. It’s pretty, but it’s also effective at making the development of invasive plants that need sunlight to grow that much more difficult.

And a bit of engineering

Through its design as well the new pond should also limit the intrusion of invasive plants. The banks are steeper and the water is oxygenated by the presence of a waterfall containing sand filters that help in the retention of phosphorus.

Another fact worth pointing out, the water in this pond circulates in a closed loop. It runs off into a small stream that flows on the border with the shaded garden and then is pumped to the waterfall to return to its point of origin.

In the years ahead, this new piece of equipment will be the subject of samplings and analyses by the Jardin botanique research team. Those interventions should make it possible to keep track of its development and to implement whatever corrections we think necessary.