Earthworms are an invasive species in Minnesotan Coniferous Forests. They were possibly brought over from dirt and plants brought from Europe. Earthworms cause the fallen leaves to decay faster - This wouldn't be such a bad thing, if it weren't for the fact that it's what helps many plants grow on the forest ground; It can also be a habitat for animals that live on the ground. With these leaves decaying faster, it can cause the environment in the Coniferous Forest to change drastically, reducing the size of the available habitat for ground-dwelling animals and can also kill many plant species that rely and live on it. It can also kill many young trees, causing less trees to grow and eventually thin out in an area.