Investigations into the impacts of climate change on tree species’ phenology have been primarily utilizing remote sensing and site-specific temporal shifts. However, patterns of tree phenology in relation to genetic heritability and environmental factors have not largely been studied. In this study, we addressed the question of how genetic heritability and environmental factors affect the timing of phenological events in a common garden study.
In the early 1960s, northern red oak (Quercus rubra) seeds were collected from 32 seed-source sites across much of its native range in the Eastern US and Canada and planted in several common garden study sites across the Midwest. We observed phenological events at the West Lafayette, Indiana study site from 2013 to 2015. We analyzed the influence of seasonal weather conditions and seed-source latitude on patterns of phenology. We utilized latitude as a surrogate for the environmental gradient of their native conditions.
Results/Conclusions
In general, phenology is strongly related to seed origin. The date of spring leaf out (the first observation of 25% leaf growth) showed a strong negative relationship with latitude, with slopes of -0.352 and -0.446 days/degree latitude for 2014 and 2015, respectively. Likewise, the date of leaf senescence (50% total leaf coloration) showed a strong negative relationship with latitude for all three years, with slopes of -1.214, -1.101, and -1.692 days/degree latitude for 2013, 2014, and 2015, respectively.
In general, shifts in temperature drive among-year variabilities in phenology. Higher mean seasonal temperature led to a more negative slope (days per degree latitude) in both spring and fall phenology. Oak trees originating from northern latitudes benefit less than those from southern latitudes from a warmer spring or extended fall growing season. While patterns in the phenology across different origin latitudes were consistent from year to year, these patterns as a whole shift depending on the inter-annual temperatures. Our results show that phenology has both genetic heritability and environmental variability. Our results can be used to assist provenance selections in adapting to climate