Managing for a City Where Parks and Streets Are 20 Percent Ash

Caitlyn Clemmer

Managing for a City Where Parks and Streets Are 20 Percent Ash

Trees provide a myriad of environmental services to cities, parks, and to the public. Trees have been scientifically proven to improve air quality by intercepting pollutants, and the absorption of gaseous pollutants through the leaf stomata.  They can also provide shade and windbreaks to buildings, which lowers indoor heating and cooling costs, and reduces the pollutants created during energy reduction. Although the planting and managing of trees in large urban forests can be costly, they are known to improve human health, increase property values, and decrease crime rates. The benefits of trees significantly outweigh the negatives of the cost (Anulewicz et al 338).

In Milwaukee, Wisconsin, an ash tree inventory was taken and resulted in 1,450 ash trees growing in public spaces throughout the city. All of these trees are at risk of being killed from the emerald ash borer (EAB). EAB was first discovered in Wisconsin on August 1st, 2008 and since then has been spreading fast throughout the metropolitan area (“Emerald Ash Borer Resource Guide”). As of October 2015, the closest EAB outbreak was within 10 miles of the city boundaries. To replace all 1,450-ash trees that could be killed by EAB, thousands would need to be planted to replace the lost tree cover. This non-native, harmful species was initially discovered in the United States during the summer of 2002 near Detroit, Michigan ("Emerald Ash Borer Information Network"). The insect attacks in two different stages; the larval stage, which is much more destructive, feeding beneath the bark and disrupting water and nutrient flow throughout the tree, and the adult stage, which causes minor feeding damage to the tree foliage. Once an ash tree is infested, it has almost zero chance of survival (Vannatta 199). There is current research conducted by Ohio’s Park and Municipal Services, proving that it takes five to ten years to infest and kill the majority of the ash trees in a city.  It is crucial to get rid of the insect at larval stage, seeing that is does most destruction at the beginning of its growth (Anulewicz 100). Initially, the goal of the city is to manage and prepare for EAB before it takes place and infects certain areas of the city, but managing for EAB can be tricky. The complete loss of ash trees throughout the city due to EAB would have a devastating effect on home values, quality of life, and the environment if the city does not begin to act (Knight 18).

The purpose of this city management plan is to prepare for EAB, take action before EAB infestation is discovered, and to buffer its impact on public and private property throughout the community. Three silvicultural techniques will be used to proactively manage for ash trees (Sadof).

1. Protection of high quality ash trees with insecticides
2. Removal of low quantity ash trees
3. Replacement of removed public ash trees on a one-to-one basis

When using the insecticides for the first technique it will only be used on the ash trees of high quality. Meaning the overall condition, total amount of trees, and total diameter at breast height (DBH). For the second technique, the lowest quality public trees will be removed first, followed by those that are no longer assets to the community. For the third and final technique, the removed public ash trees will be replaced with appropriate plantings selected to enhance the planting site, and add to the diversity and general health of the urban forest.

Management actions for Emerald Ash Borer

Protection of high quality ash trees with insecticides

 The first technique when managing for EAB is implementing a chemical treatment program for the ash trees of high quality and exclude the trees in poor condition. The chemical treatments should begin when EAB is detected within 15 miles of the city and be consistent with currently accepted Integrated Pest Management (IPM) plans. (Management Plan City of West Paul). The pesticide that will be used is TreeAzin. TreeAzin is a botanical injectable insecticide formulated with azadirachtin (secondary metabolite present in neem seeds.), this is a newer form of herbicide created specifically for treating EAB outbreak. In the United States, TreeAzin is registered by the Environmental Protection Agency (EPA) as a bio-insecticide and is also listed by the Organic Materials Review Institute (OMRI) for organic use. This product provides up to two-year control of EAB, with this in mind we would need to spray the already treated trees every two years to keep them at optimal health (BioForest Technologies Inc.-TreeAzin).

To go about this first silvicultural technique there will be an inventory of all the ash trees in the city to decide which trees are healthy enough to undergo the treatment, and which are not. An effective insecticide will stop additional damage, but it cannot undo damage that has already occurred and it takes time for trees to recover. Most insecticides used for EAB control act systemically - the insecticide must be transported within the tree; a tree must be healthy enough to carry a systemic insecticide up the trunk and into the branches and canopy (Management Plan City of West Paul).

How exactly can you tell if the tree is healthy or not? If more than 50% of the canopy has been killed by EAB or if the canopy appears to be thin and carrying less than half as much foliage as it should, it is most likely too late to save the tree (Knight). The ability of trees to recover from low to moderate EAB injury can vary, depending on the extent of the damage and which control options are used (Vannatta 200). There has been many studies that have shown if the canopy of a tree is declining when insecticide treatments are initiated, the condition of the tree will continue to worsen during the first year of treatment. If treatment is effective, the tree canopy will usually begin to improve in the second year of treatment. This gap in the reversal of canopy decline reflects on the time needed for the tree to repair its vascular system after the EAB infestation has been reduced. If the trees are assessed properly then the healthiest trees will get the treatment, and the others will not resulting in over all good urban forest health.

 Removal of Low Quantity Ash Trees

For the next technique we need to assess and determine the degree of infestation and health of the remaining ash trees. The ones that will be removed are of weak health and will not be able to handle the chemical treatment. Once EAB has attacked and killed the tree then they will be removed. We need to keep in mind that ash wood is brittle by nature and removals will need to be done in a short period of time after tree death. Removing trees can be a very timely thing so the trees that will be removed first will be the ones in the parks and open spaces that are adjacent public areas. Ash trees that are far away from human activity are to be left to fall on their own.