Timing is everything! Insights from Douglas-fir response to the 2021 heat dome
| Authors: | Andrea Watts, Connie Harrington, Richard Cronn |
| Year: | 2025 |
| Type: | Science Findings |
| Station: | Pacific Northwest Research Station |
| Source: | Science Findings 272. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 6 p. |
Abstract
Douglas-fir is the primary timber species in the Pacific Northwest. Successful reforestation after wildfire or harvest requires planting Douglas-fir seedlings that will thrive in that location. Different populations of the same species have slightly different growth habits. Selecting the right seed source for a site is critical to success.
The Pacific Northwest’s unprecedented heat dome in 2021 created June temperatures that were 35 to 45 °F higher than average. Connie Harrington and Rich Cronn, scientists with the U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, used this heat event to determine if extreme heat causes Douglas-fir to stop growing earlier in the season than under “normal” temperatures and if different seed sources responded differently to the extreme heat.
They found that diameter growth stopped early in 2021 compared to other years. In 2022, for example, summer temperatures stayed within the historical average and trees grew 125 to 370 percent more than in 2021.
Across all sites, location and seed source determined when trees experienced early growth or cessation. Trees on lower elevation sites grew earlier in the year and later in the fall. Seed sources from sites with continental climates (cold winters, hot summers, and little rainfall) had substantial early season growth. These findings are helping to ensure the productivity of public and private forests in the region.