Photos reveal how trees are ascending Rockies
Images taken century apart underline climate change, researcher says
The towering crags and peaks of the Canadian Rocky Mountains have been getting steadily greener over the past century, according to a new study.
“They are kind of becoming the needly or leafy mountains at this point,” said lead author Andrew Trant, an ecologist at the University of Waterloo.
The researchers stumbled across a collection of 120,000 historic images — mainly high-quality, glassslide photographs — from early cartographic surveys of the Canadian Rockies, which they were able to compare with modern images of the exact same scenes taken nearly 100 years later.
“In about 90 per cent of the cases the trees are growing higher up the mountain and in greater numbers, so more individual trees,” he said.
Areas that were once covered by stands of low-lying, sideways-growing trees, gnarled and tortured by the elements, are now growing upright, they found.
“Conditions have improved enough that these same individuals have turned from a prostrate, craggly thing into an upright tree,” he said. “What’s likely is that as things are warming they are able to do something they couldn’t do before and they are starting to grow upwards.”
The researchers identified 81 images from the collection that clearly showed 104 treelines, along with the density and form of the forest in areas throughout the mountain range. Unlike patchy written records from that time period, the pictures are unambiguous evidence.
“It’s a scientist’s dream to get a data set like this,” said Trant.
Only a handful of locations showed stable or retreating forest and it is not known whether events such as fires or human disturbance played a role in those changes.
Many parts of the Rockies would have passed from Indigenous stewardship to the control of European colonizers during that time, with accompanying changes in use and fire suppression.
“We are looking at two points in time, so we have to be cautious about how we attribute the drivers of change,” he noted. In the past 30 years, winter temperatures have increased by about 4C on average in the areas examined for the study, “but the most profound change appears to be recent.”
The combination of warmer temperatures and higher treelines is pushing alpine species into a shrinking space at higher elevations and north of their usual range.
Some of Canada’s iconic species could be affected by changes to this delicate ecosystem, said co-author Brian Starzomski. Grizzly bears in the Rocky Mountains make extensive use of alpine areas, where their dens are often found. Rabbit-like pikas could also be forced out of their mountain habitats by forest encroachment.
“Many caribou in this region are heavily dependent on high-elevation forests in the winter, and with so many other threats to their existence at the moment, changes in forest structure may negatively affect them,” he said.
The Whitebark pine occupies the space above most other tree species under normal circumstances, but that habitat may disappear as other tree species creep into higher elevations, he noted.
“Whitebark pine is especially important because it provides nutritious and plentiful seeds — often
As things are warming they are able to do something they couldn’t do before and they are starting to grow upwards.
called pine nuts — for species like grizzly bears and Clark’s nutcracker,” he said.
A century from now the Rocky Mountains may look very different from their popular postcard images.
“Looking forward 100 years, some of these rock faces will still be barren, but wherever it’s possible for trees to grow, with the potential for soil, there will be trees,” said Trant. “I think they are going to look like very different mountains.”
The combination of climate change and fire damage has already transformed some Alaskan coniferous forests into leafy aspen, because the conifers just don’t thrive anymore.
“They are seeing a transition from needled forests to leafy forests and something like that could be possible for the Rockies, too,” he said.
The study — A century of high elevation ecosystem change in the Canadian Rocky Mountains — was published in the journal Nature Scientific Reports.