PS 32-21
Buying time: The potential role of biocontrol in the recovery of native vegetation after a pest invasion
Although the effects of biocontrol on a forest pest are usually measured for the affected species only, these effects can propagate through the entire community. In the case of the introduced pest Emerald Ash Borer (EAB), larger ash trees (Fraxinus spp.) are preferentially attacked by the pest, resulting in high mortality. The usually abundant ash seedling bank responds rapidly to openings in the canopy and populates the sapling layer. If these saplings are then affected by EAB, other fast-responding species, many of them weedy and invasive, can take over the ground and sapling layers and outcompete other slower growing, usually native, species. However, if EAB biocontrol agents are released, the sapling layer of ash trees may persist longer, buying time for the native community to respond to the new conditions before weedy and invasive species proliferate. We collected vegetation data on forests affected by EAB in 2013, 1) without biocontrol and 2) where two EAB biocontrol agents, Tetrastichus planipennisi and Oobius agrili, are known to be established and spreading since their first release up to seven years ago. Using release data, distance between plots, and vegetation surveys, we analyzed the effect of EAB biocontrol on the recovery of native vegetation.
Results/Conclusions
Biocontrol was found to have a significant positive effect on the presence of ash saplings. The abundance of ash saplings was associated with the percent of forested area around the stand, and it had a significant positive effect on the abundance of native seedlings. The percent cover of weedy/invasive groundcover and saplings had a negative effect on native species recruitment. Even if it does not prevent further EAB infestation, our study indicates that the release of biocontrol agents can have a beneficial indirect effect on the recovery of vegetation.