Approaches to managing ash trees
Most ash trees that are attacked by emerald ash borer (EAB) will die within a few years of the initial attack. The only options are to treat trees with insecticide to attempt to preserve them (either for the long term or to spread out removals), or to remove them before they become hazardous. The three basic approaches are:
- Ash tree conservation: A portion of the ash tree population is treated with insecticide, with the aim of conserving a certain percentage of the canopy, a certain number of trees, or specific trees. With this approach tree treatment criteria are selected, and candidate ash trees are ranked according to these criteria using tree inventory data. A cut off for treatment can be selected depending on the proportion of canopy to be conserved, or the number of trees budgeted for. The remaining trees are removed and replaced either before they die, or, as they become infested and die. If the plan is initiated too late in the infestation, there may be insufficient healthy ash left to meet treatment objectives.
- Do Nothing (no action): Ash trees are treated as any other tree species and are removed as they die and become hazardous. Tree replacement is conducted as per pre-existing guidelines. There is typically an exponential increase in ash tree death with time after initial EAB infestation so removal costs, though low at first, can become considerable with this strategy. Dead ash trees can become fragile and break apart quickly after death so leaving them standing can become a liability issue.
- Pre-emptive removal and replacement: In this approach all ash trees would be removed and replace with non-ash species prior to EAB arriving. This method could be cost-effective given that work is done in bulk, but the indirect costs will be high in ash-dense areas.