Robust Model Predicts Shoot Phenology of Fraser Fir under Extreme Conditions

Abstract

Fraser fir (Abies fraseri [Pursh] Poir.) is an important Christmas tree species in the United States, and understanding its phenology is important for managing Fraser fir trees in plantations or forests. Many management decisions are informed by and dependent on shoot phenology, from late spring frost protection to shearing, and from timing pesticide sprays to managing cone production. The ability to predict important phenological stages will become increasingly important as the climate warms, as is predicted for the primary regions where Fraser fir is grown for Christmas trees. Here, we report on the development of a model of shoot phenology in Fraser fir, and present one example of how this model may be applied to the problem of managing cone production. We surveyed shoot phenology at nine Christmas tree plantations in Michigan over three years, and used the data obtained to develop a phenology model of shoot growth. Derived from the beta sigmoid function and based on growing degree days, this phenology model offers a high predictive power and is robust to extremes of temperature and precipitation. When applied to cone production, our model provides guidance for timing practices that influence cone bud formation, both for reducing nuisance cones in Christmas tree plantations and for enhancing cone production in seed orchards. In addition, the model may assist with timing other practices tied to shoot phenology. The performance of our model under extreme heat and drought conditions suggests a role for this and other phenology models in predicting and mitigating the effects of climate change on tree growth and development.

Keywords

• Fraser fir (Abies fraseri)
• phenology model
• climate change
• drought
• environmental stress
• conifer reproduction
• strobilus initiation
• cone production
• growing degree days
• differentiation