Planting trees by the millions or billions, as promised by various world leaders, is an excellent idea. These miraculous plants have the power to stabilize soil, purify water, shelter biodiversity, improve public health, and provide resilience against a warming world, while capturing and storing enormous sums of carbon from the atmosphere, mitigating the horrors of climate change.

In terms of benefit for the planet, mass reforestation ranks up there with solar power and veganism. But only if we do it right—a caveat I’m concerned most of us are missing.

Let’s consider the Trudeau election pledge to plant 2 billion trees across Canada. A forest derives its strength, resilience, and productivity from the sheer variety of trees which compose it and there are countless possible combinations of species, each better suited to certain landscapes and supporting unique suites of wildlife and undergrowth. In a mass replanting of 2 billion trees, it’s essential we include as much diversity as possible.

Most replanting operations focus on trees that grow quickly and come cheaply, leading to monoculture plantations of White spruce of Red pine, which are attractive to short sighted harvesting regimes, but pitiful in their ability to support regional ecology or mitigate climate change.

In some cases, government has even planted non-native species, complicating the game with entirely new players. So, the first rule of reforestation should be to plant a sweeping variety of species, be mindful where we put them, and stick to native trees.

Also, the whole point of mass reforestation, such as that suggested by the Liberals, is to capture and store as much carbon as possible from the atmosphere. That means you need to step back and consider all the carbon involved.

Paying for these trees with money from a government-run oil pipeline, as Trudeau suggests, misses the point. That’s like making a mess for the sole purpose of cleaning it up, leaving us no further ahead climatically than when we started. We need these trees to absorb the last 150 years of carbon emissions, not the next 30.

And many of the trees presently planted in this country aren’t intended to offset carbon emissions at all, but instead destined for a clearcut 20 years down the road, either for wood fibre or biomass.

In this case again, we’re taking one step forward and another back. Planting trees to combat climate change will never work if we intend to cut them all down, capturing the carbon, then releasing it. So, when we plant this profusion of diverse, thoughtfully placed trees, they must receive immediate and abiding protection, allowing them to mature over centuries into a sorely needed carbon sink.

And we need perspective. The ancient forests of Canada, particularly the Boreal forest and the otherworldy giants of the West Coast that we’re presently destroying, contain more stored carbon in their trees and soil than 2 billion replanted trees could capture in a thousand years or more.

If we’re interested in actually halting the climate crisis and not merely courting votes, we should be safeguarding the powerhouses of carbon sequestration already under siege in this country. Using these 2 billion trees as an excuse not to protect forests older than Jesus is an evil proposition, and by far my greatest concern when I hear talk of 2 billion trees without any real plan.

Canada is a prime candidate for mass reforestation, an undertaking I support wholeheartedly. But in a country where the complexities of ecology are so poorly understood by citizens, and the urgency of climate change is so often downplayed by our leaders, we cannot afford to get this wrong.

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