The non-native pest emerald ash borer (EAB, Agrilus planipennis) has been spreading throughout the Great Lakes region, altering the composition, structure, and functioning of forests with ash trees (Fraxinus species), the EAB host. In western New York, EAB was first identified in 2008 and has had a substantial impact given that ash trees comprise approximately 20% of forest trees and with many stands dominated by ash. Here we examine the responses of forest seedlings to 1) simulated outbreaks of EAB, and 2) a restoration effort. In 2012, six stands were identified with at least 50% ash in the canopy. In each stand, we established a control plot with uninfested ash trees and an adjacent 400 m2 plot in which all ash trees > 2.5 cm dbh were girdled, simulating an EAB outbreak. In 2014, three seedlings of both ash and a non-ash species were identified in each control and girdled plot. We measured rates of photosynthesis under ambient conditions to compare ecophysiological responses in these two habitats. We later transplanted first year seedlings of native red maple (Acer rubrum) and silky dogwood (Cornus amomum ) into half of three girdled plots and monitored them for survival, growth, and physiology.
Results/Conclusions
The tree canopy in the girdled plots has been reduced 53% and the microclimate correspondingly warmer though with inconsistent soil moisture impacts. With the canopy reduction, understory cover increased 70%. In the girdled plots, seedling photosynthesis averaged 78% greater (5.2 mmol CO2/m2/sec) than in the control plots (2.9) with consistent patterns across ash and non-ash species though the girdled plots exhibited greater variation. Reduced light availability in the control plots was the driver of this pattern and explained 83% of the variation in photosynthesis rates. In the restoration project, over 200 seedlings of each species were transplanted. Mortality rates have been low but varied with respect to the presence of seedling tubes which reduce browsing and alter seedling microenvironment. After one season, there were no quantifiable differences in the understory in the restored versus unrestored half of the girdled plots. Given the compensatory growth in the understory of the girdled plots, the performance of seedlings will be critical in forest development but are thus far limited by recruitment and it is hoped that a minimal restoration effort as described here will hasten tree community development and combat the increased prevalence of non-native plants in the simulated EAB plots.