Abstract As the climate changes, coastal temperate forests in western North America are facing more rapid and extreme temperature fluctuations. This increases drought and heat stress, but also exposes trees to unexpected cold spells, potentially leading to frost damage and reduced growth and wood quality. Coastal Douglas-fir (Pseudotsuga menziesii var. menziesii) is a keystone species in western North America and is of great economical importance. Genetic selection programs have produced fast-growing seed that is widely used in reforestation. However, it is currently unknown if these fast-growing trees are more susceptible to frost, especially under different levels of competition. Frost rings, damaged rows of cells in the cambium, are a direct marker of a tree’s frost susceptibility. This study uses frost ring data from five replicated realized gain trial sites in coastal British Columbia, each consisting of three levels of genetic gain for volume, which are tested at four planting densities. By characterizing the number of frost rings across all factorial combinations, we evaluated the effects of genetic selection and competition on frost ring occurrence during the first 10 years of growth. We observed large differences in frost ring occurrence across sites and planting densities, with microtopography playing a significant role at the subsite level. Moreover, we found a negative correlation between height, diameter, and frost ring occurrence, and a positive correlation between mortality and frost ring occurrence. Our results suggest that genetic selection for volume gain did not increase coastal Douglas-fir susceptibility to frost, but higher competition may, depending on site conditions and microtopography. Understanding site-specific climatic drivers of frost ring formation is critical in the site selection process prior to reforestation, to ensure optimal growth, quality, and survival of the stand.
Damen et al. (Tue,) studied this question.