Thursday, August 5, 2010: 2:30 PM
408, David L Lawrence Convention Center
Robert P. Long, Northern Research Station, USDA Forest Service, Irvine, PA, Patrick H. Brose, USDA Forest Service Northern Research Station, Irvine, PA and Stephen B. Horsley, USDA Forest Service, Northern Research Station, Irvine, PA
Background/Question/Methods Widespread failure of oak regeneration in Pennsylvania has been linked to a number of factors including chronic deer browsing and base cation depletion caused by wet deposition inputs of strong acid anions. This study addresses the question of which factor, poor base cation nutrition or deer browsing, is limiting to northern red oak (NRO), Quercus rubra, seedling growth in Pennsylvania. Four fenced and four unfenced plots (12.2 by 8.2 m) were established at recently shelterwood harvested mixed oak stands at each of five locations across Pennsylvania. Each plot was cleared of competing vegetation and leaf litter and approximately 225 NRO acorns were planted in an interior plot (about 8 by 4 m) in May 2004. Planted acorns were covered with hardware cloth to reduce small mammal consumption. Dolomitic limestone was subsequently applied at rates of 0, 4.5, 9.0 and 13.5 Mg ha-1 in June 2004. Soil and foliar nutrients have been monitored annually through 2009. Seedling height (HT) and root collar diameter (RCD) have also been recorded annually on 50 seedlings in each plot through fall 2009. Changes in lighting were monitored annually using hemispherical photos.
Results/Conclusions
A repeated measures analysis using a restricted maximum likelihood technique showed no statistically significant (P ≤ 0.05) effects of lime treatments on HT or RCD growth of NRO seedlings through 2009. Percent open sky, usually 20 to 35%, was not a significant covariate indicating growth was not limited by light. There was a significant fence by year interaction with reduced growth for seedlings not protected from deer browsing that was variable across years. Mean RCD was 4.1 mm in unfenced plots in 2005, not significantly different from a mean RCD of 4.9 mm in fenced plots. However, by 2009 mean RCD in fenced plots was 9.3 mm compared with 7.0 mm in unfenced plots. Likewise mean HT in 2004 was 9.6 cm in unfenced plots, not significantly different from 9.9 cm in fenced plots. By 2009, mean HT was significantly greater, 34.4 cm, in fenced plots compared with 22.6 cm in unfenced plots. Significant changes in exchangeable Ca and Mg were detected in soils. Foliage samples from each plot showed significant increases in Ca and Mg concentrations starting in 2004. Deer browsing is limiting to NRO after initial seedling establishment while base cation nutrition is not limiting to NRO growth.
