To successfully reproduce, trees must open their reproductive buds at the right time to coincide with others, minimize exposure to damaging frosts, and synchronize development with soil resources. Understanding the environmental cues that influence the timing of tree flowering is important for predicting how reproduction and survival of trees will change in the future. Using over 4,500 flowering observations from 12 sites across western Oregon and Washington, Forest Service scientists created a model to predict reproductive budburst for Douglas-fir. Managers of seed orchards across the two state helped validate the model, which is now accurate to within an average of five days of observed flowering dates.
Temperature during the dormant season was the strongest predictor of flowering time, with fewer hours of forcing (warm) temperatures required for flowering on sites and during years that had many hours of chilling (cold) temperatures. In addition, genotypes from warmer, drier locations flowered earlier in common gardens than genotypes from colder, wetter locations. Warmer temperatures in the future will likely result in earlier flowering on sites that currently have high chilling; however, sites that currently experience low chilling may display no change or possibly even a delay in flowering. These findings can also be used predict optimal locations for future seed orchards. To enhance the model’s usability, a Microsoft Excel workbook has been developed that draws on the model’s projections. Users supply hourly temperature data over the dormant season to predict the timing of Douglas-fir budburst in the spring. Seed orchard managers in Oregon and Washington used the workbook in winter 2017 to plan time sensitive management decisions for spring 2018.