by Patricia Robertson
Over the last year or so, you may have noticed a small new forest beginning to rise on the barren slope that leads from Mountain View Drive to the Yukon Arts Centre.
That “forest” of aspen seedlings is the creation of instructor Scott Gilbert and his students in Yukon College’s Renewable Resources Management program.
“The idea started with discussions with the students about how we could make our program carbon neutral,” says Gilbert.
“We’ve kept track of our emissions for the last four years, so we know how many litres of diesel and gasoline we used on our field trips.”
To offset that fuel usage, Gilbert and his students decided to “roll up their sleeves” and create their own carbon offset project.
“We wanted to try and replace the carbon dioxide we put in the atmosphere by taking it out of the atmosphere. And in our case we decided to look at planting trees.”
How exactly do trees capture carbon? Trees, like other plants, produce their own food using sunlight, water from the soil, and carbon dioxide from the air. That carbon dioxide is stored as fixed carbon in the roots, trunk, and branches.
According to the Institute of Arctic Biology, forests account for almost all the world’s land-based carbon uptake, with boreal forests responsible for an estimated 22 per cent of that carbon.
Gilbert and his students wanted a situation where, if they hadn’t taken action, the trees would never have got established on their own – a situation called afforestation, to distinguish it from reforestation, where a forest replenishes itself naturally or with some help.
So they chose the sandy, treeless slope between the Yukon Arts Centre and Mountain View Drive, which was bulldozed when the original drive was built in 1983.
They considered four different tree species: pine, willow, trembling aspen, and paper birch. “You often find pine on steep slopes and we thought they might do OK in that sandy soil,” explains Gilbert. “But we figured the community wouldn’t appreciate our efforts if, 50 or 100 years from now, a fire swept up through the pine stand and burned down our arts centre!”
The ideal tree is one that grows rapidly and builds up lots of mass, either in the roots or the trunk, so willows and aspen are frequently used because they’re fast-growing.
Trembling aspen is a deciduous tree that grows very well in the Whitehorse area, is easy to start by transplanting small seedlings, and isn’t nearly as vulnerable to fire.
In fact, aspens grow so well that they cause problems for utility companies along power line rights-of-way. That’s where Gilbert and his students dug up their seedlings.
“When we went back to the power line a year later, many of those seedlings had come back – root shoots had jumped up to regrow where we’d taken the tree out. So we felt we weren’t really killing trees.”
They’ve used compost donated by the city to make up for the fact that there’s no natural soil in the centre part of the slope. “That’s one of the challenges. Trees help create soil as they grow, but the rate is very, very slow.”
In 2011, their first year, about 80 to 85 per cent of the seedlings survived, a very good rate considering that the summer of 2011 saw high levels of infestation by the aspen leaf miner.
Gilbert and his students also set up a series of experiments to find the fastest way to grow a large number of trees on the slope. For example, this summer they tested the use of water during peak droughts. “We gave half the seedlings extra water during June and July when there was a long period without rain. We’ll be comparing survival rates to see if providing water at a critical time helps them over.”
They also tried some fall planting as an experiment. “The advice is always to do your transplanting in the spring, but there aren’t many students around in May, so last year we moved some seedlings in late September, just after the growing season ended and the ground was starting to freeze.
“We had pretty good luck – again, probably 80 per cent survival.”
Many factors can slow down the growth of a tree, including stress conditions like drought or an early or late frost, as well as disease. But the biggest source of mortality, or tree death, for the aspens has been from ATVs going up and down the slope.
“It doesn’t take much activity to run over a bunch of seedlings and kill them,” says Gilbert. “About 10 to 15 per cent of the saplings were destroyed.”
Still, they’re going to plant another set of trees this fall, and will continue to collect information on their growth.
“Our goal is to get lots of trees growing and, as they grow vigorously, we’ll be able to calculate the amount of carbon that we’ve taken out of the atmosphere.”
A carbon offset project doesn’t provide immediate results. “It could be that 30 years from now, the trees will be taking up carbon that we emitted a few years ago, so there’s a time delay in our contribution,” says Gilbert. “It’s not a quick fix.”
But it’s a long-term one. The aspens will last 50 or 60 years before they get big enough to start blowing over.
For more information on aspen leaf miners, go to www.taiga.net/yourYukon/col2021.html.
This column is coordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.