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To adapt to drought, a tree can slow its water loss and reduce its growth.

When this happens, a tree can die back from the tip of its leaves or roots inward to its trunk.

This shows up in Western red cedars as dead branches, yellowing and browning leaves and “top kill,” when a tree’s top dies.

But dying back doesn’t work forever. If drought conditions occur for long enough, diebacks become dieoffs.

“Not growing as much is a successful strategy to live, but it’s also an indicator that a tree is at risk of dying,” says study coauthor Henry Adams, assistant professor at the School of the Environment at Washington State University.

Both the current study and the government report failed to find a biotic agent that could be responsible for the dieback. This isn’t surprising.

Western red cedars are naturally resistant to insects and fungi.

This resistance, and the tree’s evenly grained wood, has helped make the tree worth more per foot than the Pacific Northwest’s leading timber tree, Douglas-fir.

The tree also holds a special cultural significance.

Many Northwest peoples consider the tree a gift from the creator. The region’s original inhabitants call the tree, “Long Life Maker,” “Rich Woman Maker” and “Supernatural One,” among other names.

For millennia, the region’s indigenous peoples have used Western red cedar to make homes, canoes, fishing gear, weapons, clothing, art and medicine.

The Western red cedar is sometimes classified as a giant arborvitae. “Arbor vitae” means “tree of life” in Latin, a name also reportedly used by local indigenous cultures.

Yet despite its cultural and economic importance, not a lot is known about the Western red cedar. The tree is largely “understudied,” according to sources interviewed for this story.

What is known is Western red cedars are not “true cedars,” like those found in the epic Gilgamesh – which are in the genus Cedrus and members of the Pine family. Rather, the Western red cedar (Thuja plicata) is a member of the Cypress family, the same family that includes coast redwoods, giant sequoias and junipers.

Yet while other members of the Cypress family—including junipers and giant sequoias—are legendary for their drought tolerance, Western red cedars are not.

The trees have been shown to be highly sensitive to drought. And this makes them especially vulnerable to climate change, which is predicted to lead to more droughts in the Pacific Northwest.

While the current study demonstrates that a recent climate event – drought – has caused the Western red cedar dieback, it does not conclude that human-caused, or anthropogenic, climate change is to blame.

This isn’t because the researchers tried but failed to prove a connection between Western red cedar mortality and anthropogenic climate change. They simply didn’t look for one. Doing so would have required a larger “attribution” analysis.

“People used to say you can’t tie just one individual event to climate change,” says Adams. “Well, you can. You just have to do your homework. And we haven’t done the homework on that, so to speak.”

The study also doesn’t rule out climate change as the ultimate cause of the Western red cedar dieback either, and neither do its authors.

The study concludes that the recent Western red cedar dieback could be an “early warning” that future droughts will lead to more Western red cedars deaths.

To nail that point home, the study’s working title is “Canary in the Forest?”

“I think Western red cedar has been shown to be more drought-sensitive than a lot of its neighbors. That’s why I put the question mark on ‘Canary in the Forest,’” says Andrus, “because I really don’t have the answer to that question [the dieback’s connection to climate change]. But it does seem like a possibility.”

Adams says it’s too soon to try to attribute the Western red cedar dieback to climate change.

However, he says, the current dieback could provide us a glimpse into what climate change is likely to do to the species in the decades ahead.

“Without being able to back it up, I don’t want say ‘it is climate change that caused this,’” says Adams. “But I will say this is what climate change is going to look like. This is what it is supposed to look like in the Northwest.”

Adams says the drought years examined in the study can be considered as a glimpse into the region’s future.

Consider precipitation.

The Pacific Northwest is known for its rain. But that precipitation is seasonal.

Precipitation tends to fall from October to June. While the dry period normally runs from July to September.

But, as the study notes, the back-to-back drought years associated with the Western red cedar dieback included years during which warm and dry conditions started as early as May and June. This lengthened the time the trees were growing without water from the sky by two months.

Climate predictions look similar.