Old B.C. trees produce mutations over time that could be key to growth success

Researchers collected DNA from the tops of some of Canada's tallest trees to search for mutations that could provide evidence of how the ancient forest giants evolve to survive.

It involved ascending 20 Sitka spruce trees on Vancouver Island, averaging 80 metres tall and ranging in age from 220 to 500 years old, to reveal that the old-growth trees developed mutations to their genetic code as they grow and age.

Sally Aitken, associate dean in the faculty of forestry at the University of British Columbia, said they wanted to know whether mutations that occur during growth as opposed to those during reproduction could add up to substantial changes for the trees.

"To do that, we went to some of the tallest trees in B.C.," she said of their research in Carmanah Walbran Provincial Park.

"We sampled the bottom of the trees and the tops of the trees and looked for places where the DNA code was different between the bottom and the top."

The results of the research appeared in the June edition of Evolution Letters, an open-access, peer-reviewed journal that publishes new research in evolutionary biology.

Peeling back history

Aitken said three professional tree climbers were hired to scale the spruce trees, while the researchers stayed on the ground collecting and analyzing the samples.

She said the towering trees appear largely unchanged over hundreds of years of growth, but peel back bark and examine needles and the complexity begins to reveal itself.

Trees have long life spans, and their evolution can't be studied as quickly as animals, but tracking what's called somatic mutation rates can offer evidence of their ability to thrive and survive, she said.

"They've been around for hundreds of millions of years," Aitken said. "They're very successful ecologically and evolutionarily."

The research is the first evidence of the large amount of genetic variation that can accumulate in the trees over centuries, she said.

Scientists have long known about mutation growth over time, but little about its frequency and contribution to genetic variation, Aitken added.

"One big, old tree could have 100,000 mutations or in that order of magnitude across the whole tree."

Aitken said it doesn't mean the trees could immediately adapt to different conditions, but it is a mechanism for them to produce genetic diversity over time.

Their research may provide insights into what part the mutations could play in how trees often adapt to local climates or developresponses to bugs and pests, she said.

"They are very successful, and this is one of the ways that may have contributed to their long-term success over eons," Aitken said. "What we can see here is that within an individual tree, a very large, old tree, we see diversity being generated that can then potentially contribute to evolution."

Aitken said wood is a necessary product and used worldwide, but the old-growth forests deserve more protection.

"I think we should be conserving a lot of old growth, and not because of the genetic diversity in these trees per se, but because of the very important functions that these trees serve," she said.

"The ecological functions. The carbon sequestration. The habitat they produce. And they're wonderful places."