Montreal’s leaky pipes could accidentally be keeping trees lush and green

Montreal's famously leaky water pipes could be the reason why the city's tree canopy remains lush and green even when it hasn't rained.

Maple trees drink about 50 litres of water every day, and it seems some of their hydration is coming from Montreal’s crumbling infrastructure.

About 25 per cent of the city’s tree canopy is made up of big maples, and though city workers water them every day it’s just a drop in the bucket of what’s needed.

Some researchers at the Université du Québec à Montréal (UQAM) asked themselves why big maples remain so green and healthy even during periods with little rain and lawns go dry.

“Especially in the street where they had very little soil where rain can go in. It’s a lot of impervious surfaces all over them,” said researcher André Poirier.

In his lab, Poirier started testing samples taken from maple trees on city streets and comparing them to samples taken from parks. He says he was surprised to find the presence of an old lead isotope in the city samples that was not found in the trees growing in parks.

“It’s like a fingerprint, essentially, of the metal. And we can trace the source of that. So we think that this old lead is coming probably from the, the old leaded pipes,” said Poirier.

According to the city, 83 million cubic metres of water leak from the city’s water system every year – more than enough to sustain the trees.

That’s no surprise to Lachine Mayor Maja Vadonovic, also the city councillor responsible for water, who said she “always thought that was happening.”

“It’s not our objective to have leaky pipes to help the trees,” she said.

The city is actively working to reduce the amount of leakage and cut it by 50 per cent since 2014.

But in the meantime, Poirier says it’s giving city trees an advantage over park trees.

“One of the conclusions of that paper is that the trees from the streets are actually more robust when there’s a drought because they don’t need the rain. They don’t have access to it in the first place,” he said.

“So they can live very happy, even though there’s no rain at all.”