Scott Swanson
Trees, especially those along some local highway stretches, have suffered from the record-setting heat Oregon has experienced this summer, experts say.
“It’s been a super hot and dry summer,” said Sweet Home District Ranger Nikki Swanson of the U.S. Forest Service. “Early-season triple digit temperatures caused stress to trees that are not used to seeing such warm temperatures at that time of the year. We have noticed heat stressed trees throughout the Sweet Home Ranger District.”
The record-setting temperatures experienced by Sweet Home and in major cities in the Willamette Valley in late June, were the highest since record-keeping began in the late 1800s.
“I’m in shock. Astounded. Sort of in disbelief, to be honest. I really wasn’t sure this was actually possible here,” Colby Neuman, a meteorologist with the National Weather Service’s Portland office, told OPB at the time.
The U.S. Army Corps of Engineers, which records weather data at Foster Dam, recorded 112 degrees on June 29, but thermometers around town displayed even higher temperatures that weekend.
Sunburn damage to conifers along Highway 20 in Cascadia, known as “sun scorch,” is particularly evident in an inordinate amount of browning needles, particularly on the faces of the trees that get the most sun exposure, said Milt Moran, president of Cascade Timber Consulting, which manages some 100,000 acres of Hill Timber land in the Sweet Home area.
“We haven’t seen it everywhere, just in certain spots,” Moran said last week. “In Cascadia, where trees really got extreme heat, you see it on the south and west sides. The north sides still look good.”
Moran said CTC also lost seedlings to the “extreme heat.”
“We’re hoping for some fall rains, good winter rains to bring it back,” he said.
Christine Buhl, an entomologist for the Oregon Department of Forestry, said the scorching occurred because “trees didn’t have time to adapt.”
“Part of the impact was it was so hot, so dry for so long,” she said. “But the other major impact was because it happened so fast. There are a lot of ways for them to transition to warmer temperatures, but this happened so fast.”
Buhl, who said she had just participated in an aerial survey to gauge damage to local forests last week, said the most damage seems to have occurred in places where trees are not used to extreme heat, particularly in coastal forests.
“We saw the highest damage in places that don’t normally have those kinds of temperatures,” she said. “The Sitka spruce along the coast are definitely not used to such hot temperatures. The pines and oaks weren’t as damaged. Douglas firs – we don’t think of them as drought intolerant, but this has been so on-going, they’re getting really stressed, too.”
The heat stress, she said, can cause collapse of vascular tissues in trees, the main transport systems of plants, which transport water and nutrition from the roots upwards through the plant.
“The heat causes things we can’t see,” Buhl said. “We may see trees dying next year from what happened this year.”
Though some call the heat damage “sun scalding,” that term, according to Wikipedia, actually refers to what happens most frequently as a result of reflected light off the snow during winter months.
The damage in such cases will appear as sunken or dead bark on the trunk of the tree, then later in the tree’s life the bark might fall away, revealing dead tissue in the tree’s cambium layer, which opens the tree to infections.
Swanson said she first started noticing the sun scorching in July.
“Each time I drive up (into the Willamette National Forest), the symptoms are worse and worse,” she said. “The damage is continuing to manifest itself.”
Moran said damage seemed to be more prevalent in areas “where there is not good air drainage, or next to highways, where the pavement’s there.”
Moran said this is the worst heat damage he’s seen in 48 years in forestry, but he’s optimistic that if the area gets adequate precipitation, most damaged trees will bounce back.
“I don’t think it will be a real setback,” he said. “Trees don’t usually retain a lot of needles for a long time. The needle burn is sort of widespread, so I’m hoping it will not slow the growth down or kill the trees.
“We’re hoping for some measurable rain.”
Buhl said that even where they’ve been burned, a lot of trees have buds that have opened, “new growth.”
“I’m hoping a lot of trees will pull out because the singeing wasn’t entirely on the crown, but there’s really no way for us to know,” she said.
Property owners can take steps to protect trees from heat, by watering them correctly and by clearing competing growth. She said ODF and the Oregon State University Extension both advise giving yard trees “a long, slow soak” once a month, but to keep it consistent.
“These trees – especially big trees – they take a lot of water,” Buhl said. “They need a lot more water than just turning on the yard sprinkler.”
She said consistency is key: “If you do it one month, then don’t do it the next month, it can send a tree right into shock.”
She recommended people visit tinyurl.com/odf-foresthealth for more information.
Also, Buhl said, fertilizing trees is not advised to try to counteract sun scorch.
“It won’t green up the red needles,” she said. “Those are lost.”
Landowners are wise to plan their landscapes, choosing appropriate species for the site and spacing them correctly and strategically.
“Clearing grasses and blackberries can be helpful,” she said. “Those compete with the tree for water.”