After the Ash Trees: How One Beetle Changed a City Greenway

Surveying the Millbrook Greenway

1The Millbrook Greenway is a paved trail that follows Alder Creek for 2 km through the middle of a city. Until a few years ago, green ash trees made up most of the trees along the creek, and their leaves shaded both the trail and the water in summer. Green ash was a popular city tree because it grows fast and handles dry, packed soil. In 2020, city foresters found emerald ash borers on the greenway. This small green beetle was brought to North America from Asia by accident. Its larvae tunnel under the bark of ash trees and cut off the flow of water and sugars through the tree, and most infested ash trees die within a few years. For safety, the city cut down dead ash trees near the trail.

2Since 2021, the eco club at Lakeview Middle School has surveyed the greenway each season with city forester Abena Mensah. In winter, club members walk the trail at dawn and count woodpeckers, birds that search bark for insects, including beetle larvae. In June, they count the kinds of wildflowers blooming in 10 plots. Many of the wildflowers that grow along this trail need some direct sun to bloom well. In midsummer, they count the live ash trees and use a phone app at 20 points to measure shade, the percent of the sky blocked by leaves (Table 1).

3A temperature logger tied to a rock in a deep pool of the creek records the water temperature all year. In the fall, the club also scoops a net sample of insects from under the rocks in a fast, shallow part of the creek and counts stonefly nymphs, the young of an insect that lives in streams. Most kinds of stonefly nymphs need cool water that holds plenty of oxygen, and warm water holds less oxygen than cool water (Table 2).