Research Shows Climate Change Effects on Local Native Trees

At the Portland Urban Forestry Division's 2019 Tree Summit on Oct. 26, city urban foresters presented findings from the recently completed Park Tree Inventory. The survey reveals stress among native western redcedars, not a surprise to those of us who've noticed the brown foliage on these trees around town. Their decline is backed up by research that was also presented at that gathering. Tree summit speakers including Aaron Ramirez, a professor of biology/environmental studies at Reed College, and Christine Buhl, a forest entomologist at the Oregon Department of Forestry, pointed to higher summer temperatures and droughts as causes for the poor condition of many western redcedars. Their browning is occurring not only in our parks but, more troubling, in our forests, where historically these trees have had ideal conditions in which to flourish. Researchers have also noticed a decline in the health of bigleaf maples. Hotter temperatures increase hydraulic function loss, said Ramirez, referring to a tree’s vascular water-carrying system. High temperatures cause air to enter the system and block water flow. “This is what kills trees when we forget to water them when we go on vacation,” he said.

Or even when we forget while home: In the past, native water-loving trees like western redcedar did not need summer watering. In today’s climate, they--and most of our other trees--do. See Ramirez's presentation here and Buhl's presentation here.