By Colleen Matula and Robert Godfrey
Wisconsin Department of Natural Resources
WISCONSIN – The moist black ash forests of the Western Great Lakes face significant challenges. The arrival of the emerald ash borer (AE), combined with various stressors related to climate change, presents unique challenges for forest managers to maintain wetland forest systems.
While black ash trees have historically been a species of low economic value in Wisconsin, they have historically provided many ecosystem benefits to rare species, hydrology, and water quality. Significantly, black ash has always had cultural significance to Native Americans. How to adapt forest management practices to protect them?
Colleen Matula, a forest ecologist and MNR silviculturist in Ashland, is leading a Great Lake Restoration Initiative (GLRI)-funded project to develop effective silvicultural strategies to maintain the resilience of black ash forests in Lake Superior basin wetlands.
The project is trying to determine which species can be successfully propagated following the loss of black ash from the landscape due to the emerald ash borer, while at the same time determining which of these species are most likely to resist the effects of climate change. . Answering these questions about maintaining forest cover and water flow despite these threats is complicated.
“We are concerned about the loss of forests and the impacts on forested wetland systems,” Matula said. “We need to know what species will tolerate these sites and if we can keep these wooded areas. Our goal is to prevent them from turning into invasive shrubs or grasses.
Humid black ash forests are complex ecosystems. Several types of habitats exist in the northern part of Wisconsin. You can find them in large, isolated wetlands and in drainage channels along streams. They cover over 700,000 acres in the state, mostly in the north. They are crucial for the recycling of water and nutrients, and their possible replacements will require careful study.
“We see these stressors coming down the pipe, and not all northern counties have the emerald ash borer that we know of, but we still need to prepare for the emerald ash borer infestation in every county and to ash losses throughout the forest,” Matula said.
The emerald ash borer is a green beetle native to northeast Asia that feeds on ash tree species. Females lay their eggs in crevices in the bark of ash trees and the larvae feed under the bark to emerge as adults after one to two years. As a flying insect, the emerald ash borer can infect any ash in its path from half a mile to 25 miles a year, depending on winter temperatures. People can also spread them unintentionally by bringing contaminated firewood from an infected area to an uninfected area.
Many northern counties are trying to figure out how to manage lowland ash forests before the emerald ash borer arrives. The impact on local sites includes flooding and soil erosion and an overall decrease in forest health. One tool that can assess productivity and quality is the Wet Forest Habitat Type Classification System (www.dnr.wisconsin.gov/topic/forestmanagement/wfhtguide). Classification can help foresters identify productivity by identifying the specific types of plants present at the site.
The Matula Project is a five-year project that began in 2019. Black Ash sites have been selected in four counties: Iron, Ashland, Douglas and Bayfield. Direct seeding and planting of various tree species took place on 100 acres of harvested and unharvested wet black ash forest. The project addresses planting efficiency, prepares sites for potential changes in water flow patterns, and increases species diversity by planting a variety of tree species. The first results and recommendations should be published by 2024.
Species replacement is a complex problem involving multiple issues, from very wet soils to drier areas with good drainage, some with poor drainage, some along watercourses and some in wet areas. One of the devices Matula uses is a sounding probe that measures the depth of organic and mineral soil layers. Wetland soils are made up of several layers. Knowing more about the depth and composition of these layers can help shed light on species tolerance and hydrology. This data can help them select the right tree species for each planting environment.
Each site may have different layers throughout the soil. For example, lowland ash areas usually have a thick layer of organic mud. With this probe we can assess the depth of the mineral soil. Some sites have a shallow organic to mineral layer and better drainage. In other places, the deep organic stratification can reach more than five feet deep. Sometimes the only species that can tolerate this site is ash because it can withstand longer periods of flooding.
Not only is the depth of organic soil important, but water flow and other features around wetlands, such as landform features, can play an important role. Some of these wetlands were once stands of hemlock or hardwood, not black ash. During heavy logging in the late 1800s, areas were flooded and did not regenerate to hemlock, so black ash took over.
Some species are sown by hand in winter because they need a cold period before germinating. In January 2021, small two-acre strips were directly seeded in the snowshoe project area. This technique could be used on a larger scale with aerial seeding. Decisions on seeding techniques are based on soil conditions and how a seed tree species germinates. Some species were planted as seedlings in the spring.
“We want to see which technique is most effective, and we’re evaluating the costs of each method, rather than just the success of the species itself,” Matula said. “Sometimes it is better for a seed to germinate in its natural environment rather than in a nursery. We test all kinds of things to see what works and what doesn’t.
Surrogate species for this study included tamarack, white birch, red maple, white pine, white cedar, black spruce, bog white oak, American elm, hackberry, yellow birch and balsam poplar. Eastern hemlock is not on the list at this time due to a lack of seed or seedling availability and germination difficulties.
Throughout the project area, deer browsing is also a concern. Foresters set up exclosures (areas where animals are kept out) and unfenced areas around different tree species to examine wildlife preferences for feeding on leaves, soft shoots or fruit of different species. They also use bud caps, a piece of paper that protects the bud of the tree, to deter deer.
“A lot of people who work in the wetlands and forest waters program are worried about ash loss because we have miles and miles of trout streams that need tree cover,” Matula explained. . “When the emerald ash borer passes, it impacts that habitat.”
Hydrology, or water flow, is another critical element with the impending demise of black ash. When the emerald ash borer passes and wipes out stands, the water table rises, creating swamp-like conditions. This can cause problems with local water flow, such as flooding of roads.
Finally, black ash provides essential cover for many wildlife species.
“There are important rare species that exist in these areas,” Matula said. “When we collected data this spring, we found several rare species of orchids. We need to keep these forested areas with appropriate species that can handle the effects of climate change. In southern Wisconsin near the Moraine of Kettle, many terrestrial invasive species appear to be invading these post-EAB invasion areas, which decrease the quality of forest areas and contribute to the loss of available habitat for wildlife and fish.