We’ve all heard the horror stories of devastation wreaked by the emerald ash borer, but just what does this diminutive little insect mean to you and me? How does it affect the areas FMR is working to conserve or restore? And can firewood restrictions really make a difference?
About emerald ash borer
Emerald ash borer beetles bore into ash trees then lay their larva, which feed on the inner bark and phloem. All native species of ash are susceptible — white, black, green, and red — as well as many planted cultivars. Primary damage is caused by larvae as they feed and produce galleries within the phloem and outer sapwood. Tree mortality occurs within one to three years of initial attack
Native to eastern Asia, emerald ash borer is believed to have entered the U.S. in solid-wood packing material in the early 1990s. With no evolved defenses, North American ash are unable to resist the invasive pest, resulting in massive tree mortality. With almost one billion forestland and urban ash trees, Minnesota has the highest volume of ash trees of any state in the union according to the Minnesota Department of Agriculture. EAB has been confirmed in Minneapolis, St. Paul and a growing list of suburbs and outstate communities.
FMR manages many sites with an abundance of ash trees. Black ash seepage swamp flanks the river at Pine Bend Bluffs Scientific and Natural Area (SNA), green ash dominates floodplain forest at Hastings SNA and there’s a significant concentration of majestic green ash trees in the dry-mesic forest at Gateway North Open Space Area (formerly known as Camel’s Hump) in Cottage Grove. Ash trees are a prominent and crucial feature of the native plant communities at these and many other sites.
The extent of the damage from emerald ash borer at each of these sites will depend in part upon the proximity of the infestation center. According to the US Forest Service, reduced volumes of ash wood harvest occur in waves outward from the center of an emerald ash borer infestation. At 50-100 km distance from the center, 2 in 10 ash trees had recently died; at greater than 100 km distance however, fewer than 1 in 10 ash trees had died. Thus if we can slow the spread and number of infection centers, we can significantly reduce the borer's impact. This is the goal of quarantines, monitoring programs, and public education campaigns.
A closer look at two special places
The black ash seepage swamp at Pine Bend Bluffs SNA is relatively uncommon in the landscape and is Minnesota’s most diverse forest type. An interesting mix of upland and wetland species can be found here, including marsh marigold, fowl manna grass, skunk cabbage, and cow parsnip.
Black ash is particularly adapted to the conditions found in such seepage areas. Should they die, the only potential replacement tree would be white cedar, which, unfortunately, are notoriously difficult to grow in the wild and are not present at Pine Bend Bluffs.
According to Lee Frelich, research associate and director of The University of Minnesota Center for Forest Ecology, should EAB reach the ash in seepage swamp, there are several succession pathways:
- Other wetland trees such as silver maple and river birch could be a possibility if already present;
- Sedge meadow with mostly native species could occur;
- Reed canary grass and hybrid cattails are possible in high-nutrient areas;
- Shrubs could take over, such as natives like dogwood, alder, willow, etc, or non-native invasives such as glossy or common buckthorn.
In addition, silvicultural experts from the University of Minnesota Extension Service warn that if a wet forest site such as this loses its ash but does not have natural drainage, water table depth and flooding risk are likely to increase. And should grasses and cattails fill in the area, fire danger and intensity would also increase.
Gateway's green ash groves
Black ash is present throughout the Upper Midwest, and is often found in wet forest, floodplain and mesic systems. Its seeds are an important food for game birds, songbirds, and small mammals, and white-tailed deer and moose use its twigs and foliage. Black ash wood has limited commercial uses, but is highly valued for paneling, furniture, and specialty products.
The ash situation at Gateway North Open Space Area (GNOSA) is different. Here, ash do not dominate the community of dry-mesic oak forest where they occur. Rather, green ash (F. pennsylvanica) form groves in the wetter areas in ravines where they are highly concentrated. These "green ash groves" provide a canopy over such diverse and interesting ground flora as maidenhair and interrupted ferns, blue cohosh, and other native forbs and sedges. This assemblage of plants most surely would suffer if a wholesale and sudden loss of canopy were to occur.
In a forest near GNOSA, a couple of fairly large Dutch elm disease and oak wilt centers opened up the canopy quite suddenly. Buckthorn was able to capitalize on the situation faster than the surrounding native plants, now dense buckthorn patches fragment this forest unit. The growth of this invasive species is in line with recent research from the US Forest Service and Ohio State University indicating that non-native plant species were facilitated by increased light in the understory.
The challenge for sites with riparian forests such as GNOSA is how to manage for its ecological health in the present while bearing in mind the inevitable loss of ash canopy in the future. As restoration ecologists, we aim to stay on top of possible regeneration strategies — from planting new trees today under the old ash giants or "advance regeneration” to regeneration using gaps in the canopy or “gap phase dynamics” — while promoting enough diversity in the future canopy so there’s some level of protection if another devastating insect infestation or fungal disease occurs.
Perhaps we can slow or even reverse the decline of ash in our region by introducing natural enemies such as the small predatory stingless wasps released in St. Anthony Park, selectively protecting high value trees with systemic insecticide applications, supporting EAB monitoring programs, and promoting public education.
Be sure to take the time to review what you can do. We recommend emeraldashborer.info, the Minnesota Department of Agriculture’s EAB site, and the Star Tribune’s EAB primer, but you may also want to contact your city forester about options or plans for boulevard trees or for recommendations on how to protect special or heritage trees in your yard.
One thing we should surely do right now is get outside and enjoy and experience our ash forests while our great ash seepage swamp and green ash groves are still relatively intact. The black ash seepage swamp is located in the Pine Bend Scientific and Natural Area in
Inver Grove Heights, but maps with GPS coordinates (including coordinates of the ash swamp) can be found at MinnesotaSeasons.com. Gateway North Open Space Area is located between 70th and 80th streets and between Hwy 61 and Hardwood Ave S. in Cottage Grove. Read more…