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SILVERTONAPPEAL.COM | WEDNESDAY, SEPTEMBER 14, 2022 | 3B The Pacific NW’s ‘Trees of Life’ are dying. Now we know why Nathan Gille Columbia Insight Their branches drop gracefully, then curve up- ward to their tips. They’re conifers, yet they don’t have coarse, rough needles. Instead, they have soft, folded, scale-like “leaves,” bright green when new, darker when old. Their trunks — cov- ered in thin reddish- brown bark — can grow to nearly 20 feet in diame- ter, though they aren’t ramrod straight like a Douglas fir, but notice- ably wider at their bot- toms, where flowing but- tress-like structures form. They grow as under- story trees for much of their lives, but they can also stretch to the forest overstory, reaching heights of up to 200 feet. They’re a key part of Pacific Northwest eco- systems, though they rarely dominate the for- est, often living alongside firs, hemlocks, alders and maples. These trees are the Pa- cific Northwest’s iconic western redcedars (Thuja plicata). To many Indigenous peoples, who used the trees for houses, clothes, weapons, tools, medi- cines, art and canoes, they’re known as The Tree of Life. They’ve been recorded to live for over 1,500 years. But these trees are now dying. For at least a decade, struggling and dead western redcedars have been reported through- out the Pacific Northwest. But the cause and ex- tent of the dieback (a condition in which a tree or plant begins to die from the tip of its leaves or roots inward) have long remained unknown. Now we have the an- swers. The dieback is wide- spread, and the cause ap- pears to be climate change. What’s more, we now know that the dieback could be the beginning of the end for the species in many parts of the Pacific Northwest. Separate studies agree Earlier this year, scien- tists from the Oregon De- partment of Forestry, the Washington Department of Natural Resources and U.S. Forest Service pub- lished the results of a two-year study on the dieback. The study concludes not only that the cedar dieback is happening throughout Oregon and Washington, but also that the dieback is not the re- sult of a biotic agent — such as a fungi or insect attack — but due to cli- mate, namely the dec- ades-long drought affect- ing Oregon and Washing- ton. Columbia Insight was given a copy of the official report for the study ahead of publication by the pro- ject’s lead scientists. The study’s results are also available online on a pub- lic website. Now a second, yet-to- be-completed study from Washington State Uni- versity is arriving at simi- lar conclusions. While the government report falls short of say- ing climate change is kill- ing western redcedars, the public website refers to the drought as “climate change-induced.” But by far the most in- teresting climate change connection in the report is a reference to previous research that predicts the range of the western red- cedar will change signifi- cantly as temperatures rise throughout this cen- tury. The website specu- lates, “We could be seeing the range of WRC [west- ern redcedar] shift or shrink due to changing Healthy western redcedars are still around, but are in decline. PHOTOS BY NATHAN GILLES / COLUMBIA INSIGHT conditions that reduce the suitability of some sites for this species.” Where they are … for now Western redcedars, and plants in general, have a growing range — sometimes called a distri- bution or climate enve- lope — that’s defined by climate conditions: how much moisture they need and what temperature range they need to grow and can tolerate. The western redcedar has a range that runs west to east from the Pa- cific Ocean to western Montana, and south to north from northern Cali- fornia at the Mendocino coast to the Southeast Alaskan panhandle. There are large breaks in the range, namely the dry regions east of the Cascade Mountains’ rain shadow, where the trees simply will not grow — though there’s a small distribution in eastern Washington where the Rocky Mountains inter- sect with the state. The elevations at which western redcedars can grow vary from sea level to 7,000 feet in the south and from sea level to 3,000 feet in the north. This range, however, is expected to change, shift- ing in some regions and shrinking in others, as the climate warms. The government re- port cites previous re- search showing that by the end of this century the western redcedar’s range is likely to disap- pear at lower elevations west of the Cascades and will disappear almost en- tirely from eastern Wash- ington, shifting north and eastward into the Rockies in Montana and Canada. In western Oregon and Washington, researchers observed dieback at low- er elevations — in Oregon in the Willamette Valley and in Washington in the urban corridor running from Olympia to Puget Sound. By contrast, in the tree’s distribution in eastern Washington, die- back was observed throughout the tree’s ele- vational range. “What we’re seeing is probably true to what most [scientific] models that have been developed [have predicted], though it’s obviously not going to be exact,” says Melissa Fischer, forest entomolo- gist and lead researcher on the dieback for the Washington State De- partment of Natural Re- sources and coauthor of the official report. Trees heading north For decades, climate scientists studying the Pacific Northwest have warned that the region will experience warmer, longer summers and more frequent and severe droughts as the region continues to warm under human-caused climate change. As a result, the ranges of many plant species are expected to shift north- ward in latitude and up- ward in elevation. However, this process won’t be a smooth move- ment north and uphill— after all, trees migrate through reproduction, one generation following another, rather than by walking. Instead, the range shifts are expected to be aided by diebacks that will occur when the cli- mate outside the trees no longer matches the bio- logical needs set by the genes inside the trees. Wildfires are also ex- pected to play a role, so that by the end of this century, the region’s co- nifer-dominate forests are expected to give way to mixed conifer and de- ciduous stands, and trees now common in Califor- nia will find their ranges shift northward to the Pa- cific Northwest. Christine Buhl, forest entomologist and lead dieback researcher at the Oregon Department of Forestry, says it’s too soon to tell whether the dieback is the start of a range shift for western redcedar, adding that the observations certainly look that way. But Buhl isn’t fond of the word “shift,” which she says doesn’t quite capture what happens when a tree’s range moves up in elevation. “What we’re observing could be a range shift,” says Buhl, “but more like- ly, from what we have found, it could be a range shrinkage.” Buhl says “shrinkage” is a more accurate way to describe the elevational data, because there is less area the further up- slope a tree’s range moves. With a rise in eleva- tion, she says, “it’s going to shrink the area avail- able to [western redce- dars].” Betsy Goodrich, a for- est pathologist stationed at the Okanogan-We- natchee National Forest, report author and lead re- searcher on the western redcedar dieback for the U.S. Forest Service, says she hasn’t looked closely enough at the model pre- dictions to have a strong opinion on whether the current western redcedar dieback could be part of a range change for the trees. However, she says it’s not a stretch to conclude that if the dieback is due to drought and more droughts are expected in the future, then the trees probably won’t reestab- lish themselves in some places. “I think it’s pretty safe to say, if you see [a loca- tion where] western red- cedar is declining that’s not going to be a good lo- cation for western redce- dar if we are expecting warmer more frequent droughts,” says Goodrich. One good rain year won’t do much Western redcedars, which aren’t as good as many other trees at slow- ing water loss during warm and dry conditions, seem to be especially vul- nerable to droughts, and the researchers’ findings point in that direction. The major climate event impacting the trees, say the research- ers, has been the drought. According to the U.S. Drought Monitor, which is cited in the report, both Oregon and Washington have been in some form of drought since the start of this century. To be sure, the two- decade period included both wet and dry periods. But lack of precipita- tion alone doesn’t define a drought. Which is why the monitor, and scien- tists generally, use more complicated metrics that track factors such as soil moisture as well as heat and drought stress on plants, all of which are af- fected by warm temper- atures. Temperatures over the two-decade period were warm, trending higher than previous decades— leading to dry soils and stressed plants. Buhl says this longer trend helps explain what’s happen- ing to western redcedars. “When the trees are damaged one year,” says Buhl, “they don’t just bounce back the next year mainly because they have lost essential tis- sues that take a long time to rebuild, and when they don’t have those [tissues] to collect moisture to translocate throughout the tree, then one year of rain isn’t going to do very much for the tree because it can’t collect [mois- ture].” In other words, the trees get caught in a Catch-22. They need tis- sue to collect water, but to grow that tissue they need water … and so on. In the field, Buhl and colleagues observed this as “yellowing,” when leaves turn yellow from lack of water, “flagging,” when brown leaves and branches occur on other- wise healthy trees, “top kill,” when a tree’s top dies because water can- not reach it and as dead trees. ‘Community science’ effort The trees also don’t seem to be getting water when they need it in late spring and early summer. “Late spring water, May-June precipitation is critical,” says Joseph Hulbert, a researcher at WSU. Hulbert leads the Western Redcedar Die- back Project, a related but largely separate effort to track the dieback. (His project shares data and compares methodology in a limited way with Buhl, Fischer and Good- rich.) Hulbert says he’s reached similar conclu- sions about both the ex- tent and cause of the die- back, saying his analysis, though still in the process of completion, strongly suggests the dieback is climate-related. “It’s one of the first species to feel the heat if you will,” says Hulbert. As of this writing, Hul- bert’s project has made over 1,700 observations, recording the location of both healthy and un- healthy trees. This has in- cluded not only observa- tions of dieback in Ore- gon and Washington, but observations of dieback in California and British Columbia. Hulbert’s project was able to do this because, in addition to more tradi- tional methods, the pro- ject is in part a “commu- nity science,” or “citizen science,” effort. This means it relies on obser- vations from members of the public to collect some of its data, in this case, people with a little train- ing in what to look for and the iNaturalist app, creat- ed by National Geograph- ic and the California Academy of Sciences. The app, which is be- ing used in other commu- nity science efforts, al- lows users to geo-locate trees, identify signs of both tree dieback and health and then send those observations to Hulbert. “We’ve revealed that this is happening all the way from northern British Columbia all the way through Oregon, probably also in California, so the whole distribution [of the species],” says Hulbert. Stressed-out trees Since a biological cause (or causes) couldn’t at first be ruled out, re- searchers from both pro- jects looked for signs of insect attacks — includ- ing from bark and wood- boring beetles, or from fungal infections — in- cluding from fungi known to cause root rot. Here Hulbert’s project took a more traditional approach, working with students from local col- leges to track biotic agents. Both sets of research- ers found signs of fungal and insect damage, but only on some not most of the trees experiencing dieback. Western redcedars contain a number of anti- pest compounds, one of the reasons the trees are prized as a building ma- terial. That the trees showed signs of biotic at- tacks at all was a bit sur- prising and is itself an ar- gument for drought-in- duced stress, according to the researchers. “They [biotic agents] are secondary,” says Goodrich. “They come in when the tree is stressed. So, it does point more to stress than a biotic dam- age agent.” According to Mathew Betts, Oregon State Uni- versity professor in the College of Forestry, who was not involved in the study, being susceptible to disease is exactly what one would expect when a species’ range is shifting due to climate change. “There are a number of stressors that can be in- duced by warming or dry- ing that could affect spe- cies’ abilities to persist,” says Betts. In fact, says Betts any- where there is a mis- match between a species’ current range and its pre- dicted future range, we can expect that species will “do pretty poorly.” This and other aspects of the report, says Betts, suggest the western red- cedar could be starting a range shift. Future research The one topic the re- searchers agree needs to be examined more thor- oughly is the rate at which the dieback is hap- pening. No one yet knows how fast the dieback is killing trees, and this, says Fischer, will be a big fac- tor in when and if the trees can migrate to their new climatic homes. “If mortality and die- back occur at a really fast rate,” says Fischer, “it’s not like the trees are go- ing to have the ability to migrate. That is a very slow process.” Hulbert says he sees “assisted migration,” or intentionally planting trees where they are pre- dicted to grow in the fu- ture, as one option. As part of a new effort called the Open Redcedar Adaptation Network, Hulbert says he hopes to experiment with western redcedar seed stock from across the Pacific North- west in order to find trees that will be the most like- ly to survive in a warmer world. So far, the project has planted trees from Ore- gon in three Washington cities: Seattle, Tacoma and Renton. But, says Hulbert, this effort is just a pilot project and was not designed to be scientifically rigorous but intended to be used as an educational tool in schools. Hulbert says he hasn’t secured the funding needed to continue this and similar efforts to build on his current re- search, but that more re- search is needed to save the western redcedar. “Probably the only hope for the redcedar is to start experimenting,” says Hulbert. Nathan Gilles is a sci- ence writer based in Van- couver, Washington. The western redcedar in his backyard is named “Au- gustus” and is doing sur- prisingly well. Columbia Insight, based in Hood River, Ore- gon, is nonprofit news site focused on environ- mental issues of the Co- lumbia River Basin.