Professor University of Washington Seattle, Washington, United States
Abstract: Plant phenology has been and continues to be impacted by climate change. Process-based modeling of phenology reveals biological characteristics through interpretation of model results and parameter values. We aim to implement a process-based cold hardiness model using historical Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) data, determine if model results improve with data clustering by seed source or growing location, and interpret model results into biological meaning. Cold hardiness development in conifers is primarily driven by temperature patterns, and thus is sensitive to climate change related warming. These interpretations have applications for reforestation, assisted migration, and studies of plant phenological response to climate change.
Cold hardiness data were compiled through literature review. A process-based cold hardiness model using daily temperature inputs was applied to multiple data clustering scenarios. Model results were analyzed for goodness of fit and to determine error, efficiency, and bias. A sensitivity analysis and cross validation were performed to determine parameter sensitivity, model bias, and variance.
Data clustering by seed source improved fit compared to clustering by growing location or no clustering when applied to the full dataset. Using only temperature inputs, model results had low error when data modeled were similar. Results show that for cold hardiness acclimation during autumn and early winter, a linear growing degree function with a threshold of 10°C was adequate across testing data, as was a maximum cold hardiness temperature of -3°C. Clustering data by genotype showed improved model fit than clustering by growing location.
Interpretation of model results show that both acclimation to growing sites and seed source genetics impact cold hardiness response, but clustering by seed source genetics provided the best fit. Assisted migration of temperate conifer populations should consider genetic limitations and specifics of cold hardiness phenology. As climate change continues to expose trees to novel temperature patterns, cold hardiness should be considered as a potential risk to population success. This work draws focus to the importance of understanding dormancy phenology in temperate trees under a changing climate. Applied uses of this model can mitigate cold related risks to seedlings during production and reforestation, and can be a template for predicting phenological responses in simulated future climate scenarios.
