Temporal changes of oak species in the eastern United States

Background/Question/Methods

Oak species (Quercus spp.) are important tree species in the eastern United States. Unfortunately, in the recent decades, oaks have experienced a decline in abundance because of an inability to regenerate, which is due to a combination factors such as changes in fire regimes, climate change, and spread of invasive species. Loss of oak populations can be detrimental because they provide important ecosystem services and are keystone species. Currently, it is not well understood how individual species have changed in recent years. This study used data from Forest Inventory and Analysis (FIA) National Program to examine the dynamic of nine oak species. Changes of abundance in each diameter class were analyzed by comparing inventory data collected in the 1980s and in 2011 for each state.

Results/Conclusions

In general, a decline in smaller DBH (diameter at breast height) classes (approximately <38cm) and an increase in large DBH classes (approximately > 48cm) were observed across all nine oak species. The largest DBH classes had the greatest relative changes in states located at the edge of their ranges. The results confirmed that oak species are having difficulty regenerating because the abundance of smaller DBH classes is declining. As older trees die off there will not be enough younger trees to replace the older ones. Attentions are needed to ensure adequate recruitment of small size oaks to the large size overstory.