Emerald Ash Borer
Potential Impact

Emerald ash borer was found in Wisconsin’s Ozaukee County in early August, 2008. The good news is that this is a slow moving pest, when people do not help it out by moving it into new areas on infested items such as firewood and nursery stock. The bad news is, all of Wisconsin’s native ash species are susceptible to attack and destruction by emerald ash borer, including white (Fraxinus americana), green (F. pennsylvanica), black (F. nigra) and blue (F. quadrangulata) ash. Wisconsin's ash resource is vast both in our forestlands and the urban landscape at 727 million and 5.2 million trees, respectively.

Destruction by this pest has been limited to urban areas and roadsides in other states. Emerald ash borer has not been observed over long periods in a forested setting. Therefore, it is difficult to estimate the potential ecological and economic impacts of this pest on our forestlands, not only in Wisconsin, but throughout the entire North American range of ash.

What should forestland owners and managers be doing to prepare their ash resource for the arrival of emerald ash borer? A committee of Wisconsin Department of Natural Resources staff and other scientists has written guidelines to help forest landowners minimize potential damages. It is important that landowners evaluate the potential impacts of emerald ash borer and take action if needed. Removing all ash prior to emerald ash borer establishment in the local area is not recommended. Please see the guidelines reference below for more detailed information.

• Preparing Wisconsin's Forests for the Emerald Ash Borer - Management Guidelines for Forested Lands [PDF, 1.6MB]

The Ash Resource in Our Forestlands

An estimated 727 million ash trees occur in Wisconsin's forestlands as a component of northern hardwood, oak-hickory and bottomland hardwood forests. Ash trees provide numerous ecological benefits: Abundant seed crops provide food for birds and small mammals; black ash twigs and leaves provide browse for deer and moose; and trunk cavities provide nesting for birds such as the wood duck. Ash is also valuable to Native Americans for its excellent basket-making quality and cultural importance.

Ash species make up 6.8 percent of Wisconsin's forests by number (all live trees one-inch in diameter or larger). Black ash is the most common species, comprising 3.8 percent of all tree species, while green and white ash are 1.6 and 1.4 percent of all tree species, respectively. Blue ash is far less abundant and its amount is negligible. More detailed information on each ash species follows.

Size classes are defined as Seedling = <1"dbh (diameter at breast height) and >1' tall; Sapling = 1-5" dbh; Pole = 5-11"; Sawtimber = >11" dbh.

Ash Species

White ash

White ash (Fraxinus americana) grows throughout Wisconsin on a variety of sites, but it's most frequently found on fertile, well-drained upland sites in both the northern and central hardwood forests. White ash typically grows as an associate in other forest cover types, and only rarely as a dominant. With its white, strong, and straight-grained wood, it is the most commercially important ash species in Wisconsin. Other valued commercial properties include high elasticity and shock resistance, and low shrinkage.

Green ash

Green ash (F. pennsylvanica var. lanceolata) occurs throughout the state but is most common in southern Wisconsin. It may form pure stands or grow in association with black ash, red maple, silver maple, swamp white oak, and elm. It grows as an associate in upland hardwood stands but is most common in and around stream banks, floodplains, and swamps. Green ash wood is not as straight-grained as white ash, and thus not as commercially desirable.

Black ash

Black ash (F. nigra) is fairly well distributed over the entire state but is most common in northern Wisconsin. It most commonly occurs in wet sites such as riparian areas and swamps, and in forest cover types such as bottomland hardwoods, swamp hardwoods, and swamp conifers. At present, black ash's commercial importance is limited. However, it was historically valued by Native Americans due to its ability to split along growth rings, resulting in thin strips for making baskets, chair seats and barrels.

Blue ash

Blue ash (F. quadrangulata) occurs in southern Wisconsin (Waukesha County), but is not overly abundant. Blue ash is considered threatened in Wisconsin and is on the edge of its North American range here. It has inner bark that was used as a blue dye by Native Americans, giving the species its common name. The species prefers rich limestone hills, but grows well on fertile bottomlands. Owing to its small size and scattered distribution, blue ash is not commercially important.

Note: Mountain ash (Sorbus spp.) is not a true ash species; therefore it is not susceptible to emerald ash borer infestation.