As climate change raises the Earth’s temperature, trees — which are highly adapted to specific climates — are now trying to survive in environments too warm for them to thrive. In most parts of B.C., it is already about 1.5 C warmer than it was in 1945.
With over 300 million trees planted in B.C. every year to replace what has been logged or lost in wildfires and other natural disasters, there’s an opportunity to help forests adapt to climate change. This summer was the first time the province’s Ministry of Forestry made it mandatory that every single tree planted must be adapted to warmer climates.
Through natural selection, tree populations adapt to their specific climate, explained Sally Aitken, a forestry professor and associate dean at the University of British Columbia. The healthiest and fittest are more likely to reproduce, the less healthy and less fit are not as likely.
While forests can adapt, it’s a slow process — and the climate is changing 10 to 100 times faster than a forest’s ability to do so.
“You can picture the climates moving across the landscape much faster than the trees can keep up with them,” Aitken said.
Climate change has already affected B.C.’s forests. One example is the mountain pine beetle outbreak that killed more than 16 million hectares of lodgepole pine from 1991 to 2015. Pine beetle populations boomed after several consecutive warm winters.
Since most human-caused climate change happened after 1945, the ministry is trying to “restore [trees] back into the climate that they were in in 1945,” said Greg O’Neill, research scientist for the B.C. Ministry of Forestry.
Traditionally, reforestation companies collected local seeds in the area they planned to reforest. But these seeds are genetically adapted to past climates and are already suffering from climate change. Now, they use seed sources from climates about 2 C warmer than their reforestation site. The extra 0.5 degrees, O’Neill says, will mean the trees are adapted for a climate that is expected in about 15 years.
It’s a balancing act: they have to plant trees that will survive in the current climate and that will also do well in the future.
Still, this “assisted migration” of trees is only happening in the portion of B.C.’s forested land base reserved for timber harvesting. This means forests not slated for logging are left to deal with the impacts of climate change naturally.
This year was the first tree-planting season where B.C. made it mandatory to plant ones adapted to slightly warmer climates.
Without assistance, change relies on pollen from trees already adapted to a warmer climate blowing into these forests to pollinate the trees, a much slower process.
“That becomes a big problem,” O’Neill said.
B.C.’s forests cover 60 million hectares — or the size of both France and Germany combined. Not only does this serve as a crucial carbon sink, but it also “underpin[s] environmental stability,” O’Neill says. Trees stabilize soil, moderate temperatures, control insects, support wildlife and provide clean water.
“Without forests, we would have a very tough time surviving,” he said.