Emerald Ash Borer
During the summer of 2009 Wachtel Tree Science, Inc. conducted an ash tree inventory and identified 2,335 ash trees along streets and an additional 261 ash trees on public lands (parks and Pleasant View Golf course). This translates to roughly 28% of the city street trees being ash – well above the desired urban forestry guideline of 20% for any genus and 10% for any one tree species.
Middleton's EAB Response
Unfortunately, there is no “preferred” response to EAB, we have to look for ways to make lemonade from the lemons we are given. With this in mind, the goal of the city’s EAB program is:
“To minimize the economic and social impact of EAB and the loss of ash trees to the health of Middleton’s urban forest by utilizing the most current information to distribute costs associated with EAB over a manageable time period.”
The choice here in Middleton fits Middleton. What other communities are doing in response to EAB, fits those communities.
Removal of ash trees
The City has been conducting the removal of ash trees on public property since 2010. Replanting with a high diversity of tree species follows whenever possible. This allows existing city staff to handle over 50% of the removals and replanting in the city – greatly reducing the costs associated with contracting the workout.
From 2010 to 2014 removals have all been preemptive; removals have been based on yearly health assessments, road reconstruction projects, storm damage, and ash tree densities. Ash trees with the lowest health had to be removed first, followed by ash trees with high amounts of deadwood, and other structural defects, and ash trees compromised by utility pruning.
Ash trees that have been causing sidewalk issues, curb heaving, or other defects have often been removed as part of road reconstruction projects. This has allowed for the removal and replacement costs to be covered by the road project.
Areas of high ash density have also been targeted. For example, Spring Hill Drive (between Lynn Street and Companion Lane) had 32 ash trees in 2009; a very high density. Two or three of these have been removed each year and spread out over the length of the road, thus avoiding a clear-cut scenario. This will spread out removals over a longer time frame than would likely occur if the city were to wait until EAB arrives. The longer removal period will also lessen the visual impact of removals and spread out removal costs over time. Replacement of trees will also result in a more diversified age structure, meaning that the difference in ages (and size) between trees will result in a healthier urban forest.
Since 2014, removals have been based on positive identification of EAB in each tree. The goal is to remove infected trees as soon as they are identified to help keep the beetle population as low as possible, thus slowing the spread of EAB.
Late winter of 2016 has shown a dramatic increase in EAB throughout Middleton. This is seen through woodpecker activity as they actively feed on EAB larvae.
Why not treat ash trees?
This is a lengthy topic and filled with passion. Rightly so, trees offer many benefits to us and wildlife. Choosing to remove trees is never an easy topic when standing right in front of one. However, there is a different set of criteria for deciding whether or not to treat ash for you as a homeowner as opposed to a municipal manager. The following are the reasons for the current approach being taken in Middleton. But first;
Current treatment options
Chemical treatments fall into two categories: the method called "root drench" which is mixing the chemical with water and pouring the solution around the base of the tree; and direct injection which is the injection of a chemical into the base of the tree (similar to treatments made now for Dutch elm disease and oak wilt).
The root drench method is relatively inexpensive, can be administered by a homeowner but has to be done every year, is best used for small diameter trees (8"-10" maximum in the opinion of the City's Forestry staff). This method also takes at least 2 months before the tree is protected. It also has many variables to consider: the soil can't be too wet, but it can't be too dry; don't do it on an overcast day; the soil has to be warm enough - apply too early in spring and it won't work...
The injection method is more expensive, and can only be applied by licensed individuals or companies, but does last for 2-3 years and is better suited for larger ash trees. Uptake and protection of a tree can occur in as little as 2-3 weeks if applied correctly. It is STRONGLY encouraged that injections be made during the summer months (June-August).
Independent of the method chosen, both will have to be conducted for the remaining life of the tree, no one can honestly tell you for how long into the future you will have to treat for EAB. Also while these treatments offer protection, they are not 100% effective.
Treatment of street and park tree ash
The majority of the ash trees in Middleton are under 14" in diameter at breast height, roughly the size of a frozen pizza you buy at the store. This is an important point. Treatment prices roughly cost $6-$10 per inch diameter (2016 rates). For that 14" tree, one treatment would then cost between $84-$140. That same 14" tree can be removed by city staff (no cost) and stump ground out, new tree purchased and planted for around $350 (2016 rates). From a cost standpoint, removal and replacement of ash smaller than 14" makes more sense. I can guarantee that the new tree will not succumb to EAB, the same cannot be said for treating the tree for the rest of its life. Also, as a municipal manager, I want to use tax money in the most appropriate manner. For these size trees and smaller ones, that would be removed and replaced.
Larger trees are a different story. Ash under power is not good, utility pruning is not healthy for the tree and creates a liability over time. These should be removed regardless. Areas of high density also should have a certain number of ash removed to promote diversity and allow for new trees to grow. Once those newly planted trees are larger, discussion of removing the remaining ash could be discussed. From here treatment may be a possibility, although at this time (Spring 2016) Middleton is not treating any publicly owned ash trees. Ultimately the decision to treat or not is up to the common council and approval of funding.
Replanting of trees
While the removal of the ash tree population is unfortunate, this is an opportunity to diversify Middleton's urban forest. The City strives to replant every tree if possible. Cases that prevent trees from being replanted are ordinance restrictions regarding intersections and signage, no planting within 10 feet of underground water/sewer lines, or within 15 feet of a driveway.
Urban forestry principles promote diversity. This is calculated by the percent of any given tree type. The goal is to not have more than 20% for any one tree genus and 10% for any species. This means that all maple trees (or oak, locust, linden, etc.) will not exceed 20% of the total street tree population. The removal of ash and diverse replacement gets us closer to the goal. A high level of diversity also provides a level of future security due to the fact that if a new threat to trees is discovered (be it insect or disease) there will no longer be a large number of any one tree species present on our streets.
So what will Middleton replant with?
Our most current tree inventory shows that maple trees are over the recommended 20% and honeylocust trees are close to that as well. Does that mean no more planting of these two genus? Not necessarily. Consideration will be given to the surrounding tree species of the area, and if for example, there are no maple trees nearby, a new maple tree may be appropriate. At the same time, the City would like to add diversity and even try some new species that are underrepresented or not present at all in the city now. Think of it as a "salt n' pepper" approach; use of a number of known species that will work as street trees with a few experimental ones scattered where appropriate and fitting to the site.