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Yellow cedar ‘declines’ in Southeast

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The Tongass National Forest makes up a large part of Southeast Alaska and is one of the wildest places in North America.  But some of its trees are dying.

Depending on where you are in Southeast, there’s Sitka spruce, hemlock, and in certain areas a type of tree called the yellow cedar.

It’s distantly related to the red cedar, but as tree pathologist and ecologist Paul Hennon explained, they had some family differences a long time ago.

Yellow cedar foliage and wood block – Photo by Shady Grove Oliver/KSTK News

“I was just at a 6th grade class and we were discussing with the students how you tell a yellow from a red cedar. They’re actually related. They’re both in the Cypress family. But that’s an ancient plant family and there were pretty close relatives of both of those trees that lived 150 million years ago in the Jurassic period with the dinosaurs. And so, although these two trees look quite similar, they actually branched off from each other pretty long ago and are fairly unrelated,” said Hennon.

Hennon put samples of both types of cedar down on the table between us.  Each one has a strong and distinct aroma. But, the fragrance of the yellow cedar is overpowering.

“Why would a tree invest so much energy into all these aromatic, sweet smelling compounds? The chemistry that it has. They’re defensive in that they slow down the growth of the fungi that would cause wood decay inside the live trees and also they repel insects. So they’re biologically really active. And they’re really key defenses for some tree that needs to live for a millennium,” said Hennon.

Unfortunately, that aroma isn’t enough to defend the cedar against climate change. Higher temperatures and changing weather patterns are making it harder for the yellow cedar to survive in many parts of Southeast Alaska.

“You know we live in this wet world.  The other thing we know—I think anybody that lives here, especially at sea level, knows—is that we live at this transition between rain and snow, and so a mild change in temperature, whether it’s at throughout a week or two or from year to year or decade to decade, really tremendously changes the amount of snow we get, because it’s either falling as rain or snow,” said Hennon.

There are two problems with this. Yellow cedar needs well-drained soil to grow the deepest roots it can. Although it’s a large tree, it has fairly shallow roots.

When snow piles up on the ground above the roots, it insulates them from the cold air. Without this protection in winter, the roots freeze and the tree dies. This is called yellow cedar decline. With rain instead of snow, the ground is soggy and the roots are especially shallow.

Now, these trees have been around since the dinosaurs. So they’ve experienced many changes in temperature over the years.

Like other living things, they move around so they can be comfortable in their environment, especially when it changes. But they can’t fly and they can’t walk. And this time, they’re finding it hard to keep up.

“Trees adapt. They may die out in one part of the range and then maybe migrate and grow well in another part of the range.  But one of the concerns these days is that that process plays out too quickly.  The climate shifts, these shifting zones of climate, are moving faster than these trees can migrate,” said Hennon.

So why does it matter if these trees die?  They are one of the most valuable hardwoods in the timber industry.  They are used in a lot of traditional and Native construction, among other things.  And they are an important component of their ecosystems—to the plants and animals around them.

Now, scientists are thinking of ways to help these trees.  First, they have to find habitats where yellow cedar could flourish, but where it’s not growing now.

“We think in these areas where it’s kind of rare say up in the Prince William Sound, or over by Juneau.  It looks to us as though there’s a lot of suitable habitat.  There’s a lot of places where yellow cedar could grow.  And it just simply hasn’t gotten there yet.  So we think this pattern of where it grows has to do with a long-term migration,” said Hennon.

Now, we have to go way back in time and all across Alaska.  In the Pleistocene, or the time period that lasted from about 2 million years ago to 12,000 years ago, most of the Alaskan panhandle was covered in ice.  However, there were a few ice-free areas on the outer coast around what is now Sitka, Prince of Wales, and Glacier Bay.

“They were ice-free at that period.  And we think yellow cedar kind of hung out in the Pleistocene in those areas, and that it’s still migrating toward the east, from those areas.  And it’s just a very slow, deliberate process,” said Hennon.

This is where the scientists come in.

“The kind of gratifying thing now is, now that we have that knowledge about what its vulnerability is, we’re working with Forest Service people in the regional office and on the Tongass—you have the Wrangell Ranger Districts—to begin to form some way of adapting and trying to use that knowledge we developed through research and put it into action,” said Hennon.

There is a pattern to the cedars’ mortality. The trees are dying in a band that stretches from Ketchikan up through Wrangell and Petersburg and over to Sitka.  So they’ve found a way to give these trees a little push in the right direction.

“The way I think about it is, it’s not moving it wholesale from one place to another.  Although there is, we’ve tried that.  We have a new planting of yellow cedar up by Yakutat.  It’s in a very snowy place where yellow cedar, hasn’t grown…is not growing now…hasn’t grown for thousands of years.  So that would be one case of actually moving it completely to another area,” said Hennon.

To help the populations already in the wet Southeast, they are just nudging the trees uphill.  They’re planting new cedar at higher elevations where the soil drains better and there’s more snow.

So what does the future look like for these trees? There are already some healthy patches of cedar near Cordova and one between Valdez and Whittier.  If they can get more trees growing further east, new communities of yellow cedar may thrive in the years to come.  But it will take a lot of work by scientists, the parks, the Forest Service, and many others to make it happen.

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