Yes, Planting Trees Can Fight Climate Change — If We Do It Right

In Paul St. Pierre’s fine novel Breaking Smith’s Quarter Horse, a Chilcotin rancher named Smith is riding home on a winter day, sometime in the 1950s or '60s. It’s so cold he hears a jack pine explode like a shotgun blast as the water within it turns to ice and expands.

Trees don’t often explode these days. The reason is climate change, which St. Pierre, a former Liberal MP, went to his grave denying.

Our winters are warmer than 60 years ago, and we seldom see the -40 weather that used to kill the mountain pine beetle and explode trees. We are a nation of forests witnessing a kind of climatic clearcutting, but we stand on the highway like the proverbial deer in headlights instead of leaping into the safety of the woods again.

A recent scientific report suggests that we could go a long way to stabilizing the climate by a simple measure: plant a trillion trees on a billion hectares — an area the size of the U.S. — and let them absorb up to 205 gigatonnes of carbon dioxide as they grow. (That’s the equivalent of more than 350 years of Canadian emissions.)

It’s an attractive idea, especially to hewers of wood and drawers of water like Canadians. We understand trees, or like to think we do, even if most of us live in cities. We may venerate loggers, but we also admire tree planters who work hard to reforest clearcuts. And we have a vague sense that all may not be well in our B.C. forests after decades of bark-beetle kill. Reforestation could be a way to restore our lost Eden.

The scientific report got a lot of media attention, precisely because reforestation and afforestation (planting trees where they haven’t grown in a long time) seem simple and doable. It’s carbon sequestration without the need for high tech or vast amounts of money.

Too little, too late?

But it’s too little and probably too late, according to Mark Maslin and Simon Lewis. Writing in the Conversation, they agree that massive reforestation doesn’t have to mean giving up farmland, and might even improve production by stabilizing the soil and rainfall.

But they think sequestering 205 gigatonnes of CO2 is unachievable. “The authors have forgotten the carbon that’s already stored in the vegetation and soil of degraded land that their new forests would replace,” they note. “The amount of carbon that reforestation could lock up is the difference between the two.”

As well, it would take centuries before the newly planted trees would store the full 205 gigatonnes of carbon, while we have only decades to curb emissions. And in the meantime the worsening climate will not be kind to young forests. Reforestation will be futile if we continue to increase our emissions at the same time as we plant trees.

And it matters where we decide to plant these trees. Not all forests are equally effective at cooling the Earth while they store carbon. An article in Nature Communications sets out the differences. “Results show that tropical forests have a strong cooling effect throughout the year; temperate forests show moderate cooling in summer and moderate warming in winter with net cooling annually; and boreal forests have strong warming in winter and moderate cooling in summer with net warming annually.”

Our dark boreal forests absorb heat in winter that would otherwise be reflected off snowpack back into space.

So reforestation would be more effective in the tropics — which could pose problems. Brazil is planning to deforest still more of the Amazon to grow beef and soybeans. Indonesia burns off its forests and replaces them with palm oil plantations. Will they clear more forests than can be planted?

People can’t always leave forests, old or newly planted, alone. In China in the 1980s, I saw newly planted saplings growing on a hillside. But they had almost no soil or leaf mould, because local peasants were collecting it all to mulch their own fields and gardens. Haitians denude their forest hillsides to make charcoal.

Still, there’s reason to hope. Efforts are already under way to reforest Central America. Mexico is spending US$100 million in El Salvador and Honduras on reforestation projects. They’re intended to keep people home and earning money instead of migrating north and annoying Donald Trump.

Reforesting Central America may have a precedent as a climate driver: Maslin and Lewis are also the authors of an excellent book, The Human Planet: How We Created the Anthropocene, which offers evidence that the loss of millions of Indigenous lives to European diseases after the conquest of Mexico actually triggered the Little Ice Age. Vast Indigenous farmlands and settlements returned to forest and jungle, absorbing billions of tonnes of carbon in the process. Not until the 19th century, Maslin and Lewis argue, did human CO2 emissions overcome the cooling effect of those new forests.

So perhaps Canada could help reduce CO2 by paying to reforest Central America, Haiti and other tropical countries, as well as our own temperate regions. If it also reduces migration pressure from the tropics, so much the better.

Urban trees as public health measure

As populations increasingly move into cities, more rural land will be available for afforestation. But the cities themselves will get bigger, hotter, sicker and less inhabitable. The answer here will also be to plant trees. The Nature Conservancy recently published a study calling for planting urban street trees. “They can help clean and cool the air, reducing harmful air pollutants and ambient air temperatures,” it noted. “They lend beauty to our streets, enhance citizens’ lives and significantly increase property values.”

Just shoving saplings in the ground won’t be enough. They would have to be protected against animals and insects. We’d have to choose the right species, resilient enough to flourish even as the climate worsens. The trees would also need to support whole ecosystems: forest-dwelling animals, birds and insects, not to mention fish in the streams and other plants in the understory. With a little tinkering, we might also come up with genetically modified trees that grow rapidly while absorbing extra CO2.

All that standing wood would be a fire hazard, of course, and a bad wildfire year can put as much CO2 into the atmosphere as industrial emissions. We’d have to develop a new science of forest management to minimize the risk, perhaps with the kind of burns Indigenous peoples used to reduce fuel on the forest floor while leaving the trees and ecosystem intact.

And as Maslin and Lewis point out, we’d have to do all this while also significantly reducing carbon emissions. The new forests wouldn’t be an infinite carbon sponge, letting us soak up an ever-increasing mess. We would still have to consume less fossil energy, whether in travel, transportation, production or agriculture. And we would also have to bring billions of human beings up to a standard of living both decent and sustainable.

So we Canadians might have to give up destination weddings in Cancun and out-of-season strawberries, but that is preferable to people in the tropics giving up their lives and those of their children.

And if the prospect of losing December strawberries seems to make life not worth living, consider the greater pleasure we might give our grandchildren and great-grandchildren late in this century. They could explore the tall green cathedrals we planted for them, finding wild strawberries growing in the clearings, and go snowshoeing in winters so cold that they might even hear a tree explode, as they did in the olden days.