Understory

Understory Without Worms	Understory With Worms

(Images from UMN 2005)

Most native species that make up the understory do not survive after an invasion of earthworms. "In a forest that previously had 20 to 40 native species, there may now only be one or just a few remaining. In addition, there is now very little plant cover, as little as 0-20% where there had been 100%. Most of the understory is now bare soil rather than a lush carpet of green plants. (UMN 2005)"

Most exotic species, including earthworms, in Minnesota came from Europe. This means that European plants have co-evolved with earthworms and are better adapted to living with them than our native species that evolved without worms. In some forests, after the earthworms invade and the native species die, some exotic species begin to invade and start the process of taking over the understory.

Shrubs, Herbaceous plants and mosses all decrease after earthworms invade. Along with tree saplings and seedlings, these plants had been rooting almost exclusively in the forest floor. When the earthworms eat the forest floor, the plant roots are left exposed. (UMN 2005)

View effects on understory and forest soil