The emerald ash borer was first seen in the United States near Detroit in 2002 and soon gained a fearsome reputation for killing every untreated ash tree it came across. Named for its brilliant hue, this insect is leaving the world less green as it spreads, and it’s spreading fast. In 2013, the insect was discovered burrowing its way into ash trees in Warner Park.
In Madison, 10,724 street trees are in treatment. Alves says that the county can plant five to 10 trees for the cost of treating one tree, so the county is pursuing an aggressive replanting policy.
Madison is also removing trees that are in danger and has increased the pace from 1,700 to 2,000 ash trees annually to be replanted with other types of tree within three seasons after removal. Almost half of all city trees being removed now are ash trees. The burden of having to remove and treat ash trees will eat up resources for other city forestry services, including annual pruning, for years to come.
Madison has seen similar tree carnage before. In the 1960s and ‘70s, Dutch Elm Disease decimated Madison’s urban canopy, leaving many streets bare. Unfortunately, when replacing Dutch elms, the city relied primarily on ash trees.
“Ash trees were a popular replacement choice,” says Alves. “A lot of street trees are riparian species, or trees that grow well near water. They are chosen because they can grow in low-oxygen soils. Ashes are hardy, cheap and easy to plant, so we planted way too many of them.”
The riparian quality that made them such obvious choices 40 years ago will have serious ramifications as they die en masse. Because they naturally grow near water, the ash population is particularly common around lakes in the Yahara corridor. That means we’ll be losing a high percentage of the canopy cover along lake shores, stream banks and rivers.
“When you lose trees from the water’s edge, you get more stream bank erosion and a lot of debris,” says Alves. “Along many of our shorelines, ash make up more than 70 percent of the trees. My main concern is as we lose those trees, you will see more erosion and more sediment in the water, which will include more phosphorus for algae to feed on. We have a lot of lakes. It is a pride of the county. This die-off will have an impact on water quality.”
Both Madison and the county are replacing ash trees with a wider variety of species. So hopefully the next time an invasive insect or disease comes through, it won’t have such devastating consequences to the overall canopy.
“One of the best things we can do is put a variety of trees in the ground for our grandchildren to appreciate,” says Alves. “Tree love is universal.”
The Madison Emerald Ash Borer Update estimates that street trees provide $11.7 million in benefits in a variety of ways, including shade that reduces cooling costs. The city’s trees intercept 115 million gallons of rainfall.
“If you lose an ash,” Alves says, “you should consider planting a replacement, but don’t plant the same tree as your neighbor. Moving forward, this is an opportunity to re-examine our policies and lay the groundwork for a healthier urban forest.”
Do you have ash trees on your property? What are you doing about it?