Ash Management Guide for Private Forest Landowners

Chapter 5The Native PlantCommunitiesMesic HardwoodSystemA Mesic stand inearly SpringGLOSSARYduff: The partiallydecomposed organic materialof the forest floor beneath thelitter of freshly fallen twigs,needles, and leaves.Earthworms & Ash: Making the ConnectionsPhoto: Julie MiedtkeEarthworms may be ‘tool of the trade’when it comes to fishing Minnesota’slakes. And they are considered rathergood friends in the vegetable garden.However, earthworms are an unwelcomeintruder in Minnesota’s hardwood forests.Minnesota’s mesic hardwood forestsdeveloped in the absence of nativeearthworms. These forests grew after thelast glaciers retreated. They contained athick forest floor that served, and continuesto serve as a perfect rooting mediumfor many species of forest herbs and treeseedlings.Minnesota has no native earthworms.In the 1800s European settlers arrived,bringing with them European earthwormspecies in potted plants. Europeanearthworms have been part of the habitatssurrounding human habitation eversince. The European earthworm invasionchanges the structure of forest soils. Theduff layer is consumed by the worms sothat the seedbed conditions on the forestfloor change from deep leaf litter to baremineral soil during summer. The soil isalso compacted, leading to more runoffduring heavy rainfall events; the availabilityof nitrogen and phosphorus isreduced.Earthworm invasion accentuates thealready negative impact of deer browsingon native plant and tree species. Combined,these changes make trees moresensitive to drought, make regenerationof some species like sugar maple andred oak difficult, lead to reduction in thediversity of native plants, and facilitateDo NOT release earthworms!Earthworms should be considered as a serious threat to nativeregeneration in the Mesic Hardwood Forest type. Earthworms arean unwelcome intruder in Minnesota’s hardwood forests.46