In 1997, Simon Fraser University used 10,000-year-old pollen to reconstruct British Columbia's warmer past. 29 years later, his evidence still warns forests could lose alpine meadows as trees climb 100 metres higher

Nearly 10,000 years ago, British Columbia experienced a warmer period that changed the province's forests and treelines. Evidence preserved in lake bottoms, wetlands and even an unexpected mountain stream log now offers clues about what a warmer future could look like, as per Simon Fraser University.

Simon Fraser University biology professor Dr. Rolf Mathewes studied ancient pollen, seeds, cones and charcoal to reconstruct those changes. His findings suggest that warming could push trees higher into alpine and sub-alpine areas, while making forests more vulnerable to drought and fire.

What does 10,000-year-old pollen reveal?

Mathewes examined pollen and other plant remains preserved in lake bottoms and wetlands, some dating back 10,000 years. Between roughly 9,000 and 7,000 years ago, British Columbia experienced a warming period similar to conditions being predicted for the coming century.

"We know that the climate was warmer in the past and how it affected forest cover, and we can use this information as an analog to predict the future," he explains.

The ancient evidence showed that forests on the south coast contained more Douglas fir, alder and bracken ferns than they do today. All three species commonly grow after major disturbances such as fire.

Large quantities of charcoal found in lake sediments from 7,000 to 9,000 years ago also pointed to widespread forest fires. Mathewes connected those fires with a warmer, drier climate, prolonged drought and possibly an increase in storms.

How did a mountain log confirm the evidence?

One of the strongest pieces of evidence came from an unexpected discovery on Castle Peak in the South Chilcotins near Lillooet.

A Geological Survey of Canada surveyor was camped on the mountain when he went to a nearby stream to collect water for tea. There, he noticed a log even though the site was about 100 metres above the modern treeline.

The discovery eventually brought Mathewes to the location.

"This serendipitous discovery helps confirm that the climate was warmer many years ago and helps confirm our theories of what happened in the past," he says. "The discovery was truly independent evidence that the climate was warmer than today. The treeline is determined largely by temperature and it was at least 100 metres higher at that time."

Fossil seeds and cones found at the site provided further evidence of ancient forests. They showed that whitebark pine and sub-alpine fir had been growing there around 9,000 to 8,000 years ago.

Could warming push forests into alpine meadows?

The evidence points to a major possible change in British Columbia's mountain landscapes.

If the West Coast climate becomes warmer, trees could move higher up mountains and take over some alpine and sub-alpine meadows. Mathewes noted that this has already been observed in parts of the Pacific Northwest, including the Olympic Peninsula.

That could change landscapes that people now associate with open alpine meadows and flowering plants. Future hikers searching for those meadows may have to travel higher into the mountains to find them.

Warming could also change the composition of British Columbia's forests. More drought-resistant Douglas fir could begin replacing western red cedar and hemlock.

"We are likely to have more forest fires of increased severity. Cedar is especially susceptible to fire and drought. In fact there is evidence to show cedar is not regenerating well in some areas now," Mathewes says.

His findings have already been considered by the forest industry when deciding which seedlings should be used to replant clearcuts.

The effects would not stop with forests. A warmer and drier climate could cause many small lakes and wetlands to dry up, threatening birds, fish and other wildlife that depend on them.

The ancient pollen, charcoal, fossil seeds and mountain log therefore tell a remarkably consistent story. British Columbia's forests have changed with climate before, and the evidence from that warmer period offers a way to understand what could happen if temperatures rise again.

For the alpine meadows, the warning is particularly striking: as trees move upward, some of the open landscapes found at higher elevations today could gradually disappear.

FAQs

What did the ancient pollen show?
It revealed how British Columbia's forests changed during an earlier warm period.

Could trees move above today's treeline?
Yes. Evidence suggests the treeline was at least 100 metres higher during the ancient warming period.