The Virginia Department of Forestry speaks

Editor's note: "In 2008, two locations in Fairfax County, Virginia not only revealed numerous trees infested by the Emerald Ash Borer (EAB), but it appears the infestations are at least 2-3 years old, meaning the invasive beetle has already had an opportunity to spread." In the essay below, Christopher Asaro, a Forest Health Specialist with the Virginia Department of Forestry, details his take on the ramifications of this latest infestation. You can skip down to;

• Introduction
• The spread of EAB, in this situation
• What Virginia Department of Forestry can and cannot do
• Implications for city trees
• Why diverse tree plantings could make a difference

The Emerald Ash Borer in Virginia

The emerald ash borer has once again been found in northern Virginia, and we all knew this day would come. Unlike the original infestation in 2004, however, eradication of the current infestation is unlikely. The 2004 infestation originated from a known source and was quickly identified before beetles had a chance to complete their life cycle and spread. In 2008, two locations in Fairfax County not only revealed numerous trees infested by the invasive beetle, but it appears the infestations are at least 2-3 years old, meaning EAB has already had an opportunity to spread. It is likely that many more infestations will be found in the coming months and years. Add the fact that it also present in West Virginia, Pennsylvania and Maryland and long term eradication at this point is unrealistic at best. The Virginia Department of Agriculture and Consumer Services (VDACS) will quarantine Fairfax County and all additional counties where the insect is found to prevent the spread of infested wood products that may harbor the pest. Slowing the spread of EAB via control of major pathways such as the unrestricted movement of firewood will certainly have value and should be pursued vigorously. However, eradication will not be pursued in Virginia.

The eventual spread of EAB across Virginia and into new states is all but inevitable. In reality, the battle was lost before it began. Detecting this insect early is extremely difficult due to a lack of effective monitoring tools. By the time damage is visible (larval galleries under the bark and D-shaped adult emergence holes), EAB adults have already moved on. It is estimated that EAB was present in Michigan at least 5-10 years before it was finally ‘discovered’ in 2002. By then, eradication was already too late. Most states that discovered the insect within their borders soon realized that it had been present at least a few years before. Then there is the artificial movement of the insects over hundreds of miles by campers bringing firewood with them to their destinations, often campgrounds in neighboring states. As well, firewood being sold in Virginia has been found to come from 12 different states and a few countries, including states which harbor EAB. [emphasis added by blog editor]

While laws restrict movement of infested goods out of counties under quarantine, it is likely that some non-quarantined counties in those states harbor yet undiscovered EAB infestations. Quarantine restrictions cannot be imposed until evidence of a pest is actually found. As we have seen time and time again with EAB, this is often too late to be effective. Most new infestations have appeared adjacent to campgrounds or major interstates. Virginia was no exception: the two new infestations were found just near the Dulles Access Road in Herndon and the town of Springfield just near I-95. This means they could have originated from just about anywhere.

With these facts in mind, what efforts will the Virginia Department of Forestry (VDOF) pursue to mitigate the impacts of this pest? In reality, there is not much proactive that can be done in natural forested settings. White and green ash combined represent 99.9% of the ash volume in Virginia, a little over 1.6 % by volume of the natural forested area in the Commonwealth (based on US Forest Service FIA plot data). It is a widely scattered tree, and is only found in abundance in isolated areas along river bottoms.

Practically speaking, an EAB infestation in the forest would not be amenable to control. Salvage would also be very unlikely unless high value white ash crop trees were present. From a forest management standpoint, salvage removal and encouraging the growth of other species would be the most practical, long-term strategy for dealing with this problem.

From an economic point of view, perhaps the greatest and most visible impact will be to the urban forests of Virginia. Trees killed by EAB will become hazardous and will eventually have to be removed and hopefully replaced. Ultimately, this could cost millions, perhaps even billions of dollars, depending on how much ash there is to remove. Surprisingly, much of the urban forest composition is poorly documented, even in some major cities such as Richmond. FIA plots do not include urban forests so each municipality is responsible for their own street tree inventory, and many of them have little or no data in this regard.

The VDOF is currently funding Virginia Tech to conduct city surveys throughout the Commonwealth. The goal is to get a 5% sample of street trees from major and minor municipalities in order to assess the overall abundance of ash within individual municipalities and throughout the urban forest of Virginia as a whole. The data from this sample is input into a computer software program developed by the US Forest Service called STRATUM, which converts the sample into a statistical estimate of street tree abundance. Some municipalities that already have excellent inventories available can also add their data to the survey for inclusion in the STRATUM analysis. Only by getting a full and accurate assessment of the urban tree resource can we begin to plan wide scale urban tree removal and replacement efforts and assess costs. Even those cities that are some years away from EAB problems would be wise to use this data as a planning tool. Gradual replacement of ash trees with EAB resistant species, as well as urban forest diversification to limit the impacts of other invasive pests, should be a major priority. After all, ash was one of the primary species used across the US to replace the widely planted American elm after city streetscapes were devastated by the spread of Dutch elm disease. Hopefully we will not make the same mistake a third time by diversifying our urban forests as much as possible and not putting too much emphasis on one species.