Predicted Responses of Genetically Improved Populations to Climate Changes Based on Second-Cycle Douglas-Fir Progeny Tests

The current planting of economically important timber species, such as Douglas-fir, mainly relies on genetically improved seeds from seed orchards. However, published research on the effects of climate change has largely focused on natural populations. To bridge this gap, data from 80 cooperative second-cycle coastal Douglas-fir progeny tests across eight breeding zones in western Washington and Oregon were analyzed. Climate transfer functions for age-12 growth were derived, showing significant results for the US Pacific Northwest. Region-specific transfer functions (Coast, Inland, and Cascade) displayed stronger correlations. Mean annual temperature and mean coldest month temperature were the most important climatic variables explaining growth. The study found that populations from slightly warmer areas tended to grow better but moving populations from colder to warmer areas by 2 °C (analogous to projected global warming) would result in an 8% genetic loss in age-12 height and a 25% genetic loss in age-12 volume. However, substantial diversity in climatic response was found among full-sib families within large breeding zones, suggesting that breeding and selecting suitable families for future climatic conditions within breeding zones is feasible. The study discusses potential strategies to adapt current breeding programs to address the impacts of future climate change while maintaining high population growth rates in Douglas-fir breeding programs.