Climate change is predicted to shift habitat suitability of major tree species in forests of the northeastern United States. In Vermont (VT), the oak-hickory forest type is projected to expand into areas currently occupied by the maple-beech-birch forest type. Northern red oak (Quercus rubra L.) is currently a minor component of forest ecosystems within VT, and is found primarily in valleys and at lower elevations. The species is presumed to be temperature-limited in the region, which is in the northern part of its range. However, red oak’s importance is projected to increase in the region as temperatures rise. We investigated whether there is evidence of an increase of red oak radial growth in VT. We examined annual xylem increment growth of dominant and codominant red oak trees at nine sites throughout VT at various elevations. We used standard dendrochronology techniques and assessed at least 14 trees per site to examine synchronous growth trends across multiple stands over time (1867-2015).
Results/Conclusions
Red oak displayed an increase in xylem basal area increment growth across all sites. Growth generally increased across the sites between 1950-2015, with a decrease in the early 1970s and subsequent increases in the early 1980s. After 1950, we found no differences in the slopes of stand-level chronologies associated with age (P=0.56) or size (P=0.98) classes. Lower elevation sites showed a marginally greater increase in growth than higher elevation sites (P=0.07), suggesting that lower elevation stands may be gradually less limited by temperature than those at higher elevations. While year-to-year variation exists among sites, largely synchronous recent growth trends suggest associations with broader climate or deposition factors common across the region. To explore possible drivers of observed growth patterns, we are evaluating relationships between growth (ring width index chronologies) and environmental factors including temperature, precipitation and pollutant deposition.