Oak Loss Increases Foliar Nitrogen, δ15N and Growth Rates of Betula lenta in a Northern Temperate Deciduous Forest
Record Type: Research Project
Project Start Date: Sept. 1, 2009
Description: Oak forests dominate much of the eastern United States, but their future is uncertain due to a number of threats and widespread failure of oak regeneration. A sudden loss of oaks (Quercus spp.) could be accompanied by major changes in forest nitrogen cycles with important implications for plant nutrient uptake and tree species composition. In this study, we measured the changes in nitrogen use and growth rates of black birch trees (Betula lenta L.) following oak girdling at the Black Rock Forest in southeastern New York, USA. Data were collected from nine experimental plots composed of three treatments: 100% oaks girdled (OG), 50% oaks girdled (O50), and control (C). Foliar nitrogen concentration and foliar 15N abundance increased significantly in the oak-girdled plots relative to the control, indicating that the loss of oaks significantly altered N cycling dynamics. As mineralization and nitrification rates increase following oak loss, black birch trees increase N absorption as indicated by higher foliar N content and increased growth rates. Foliar nitrogen concentration increased by 15.5% in the O50 and 30.6% in the OG plots relative to the control, while O50 and OG plots were enriched in 15N by 1.08‰ and 3.33‰ respectively (p < 0.0001). A 641% increase in black birch growth rates in OG plots suggests that this species is able to respond to additional N availability and/or increased light availability. The loss of oaks and subsequent increase in black birch productivity may have a lasting impact on ecosystem form and function.