PS 8-75
The interactive effect of tree-ring porosity and extreme warm years on the timing of leaf emergence
Global climate change will lead to an increasing number of extreme years, in which temperatures are anomalously high. It is well known that the timing of tree phenological events (e.g., leaf emergence, flowering time) is advancing with global warming; however, it is not well known to what extent tree phenological events will be altered by more frequently occurring extreme years. In addition, the porosity of tree species is known to affect the timing of phenological events with ring-porous species showing later phenology, on average, as compared to diffuse-porous species. To date, the potential effect of tree-ring porosity on tree phenology in response to extreme years is not known. In this study, we examine the potential interactive effect of extreme years and tree-ring porosity on the timing of leaf emergence for thirteen tree species across eight years of study (2002- 2009) using the Network of Ecological and Climatological Timings Across Regions (NECTAR) Harvard Experimental Forest database.
Results/Conclusions
We find the most extreme year (2006) of the study at the Harvard Experimental Forest yielded the greatest difference in the timing of leaf emergence between ring-porous and diffuse-porous species, averaging 11 days later for ring-porous species. However, the magnitude of difference in the timing of leaf emergence between ring-porous and diffuse-porous species does not show a strong correlation with the increasing extremity of years as predicted, likely due to a narrow range of mean annual temperatures among years when data was observed (i.e., there was a lack of anomalously warm years). We also found no correlation between the extremity of years and the amount of growing degree units (GDU) accumulated at leaf emergence. We conclude that future studies are needed to further examine the effect of extreme years on the phenology of trees with respect to porosity, using the magnitude of difference between diffuse-porous and ring-porous species, especially as this proxy could help predict shifts in competitive dynamics among co-occurring tree species in the future. If large differences in the timing of phenological events do occur between ring-porous and diffuse-porous individuals during extreme years, co-occurring tree species could experience very different growing season lengths and exposure to early frost damage.