The Forest Floor

Forest Floor Without Worms	Forest Floor With Worms

(Images from UMN 2005)

According to a study published by Ecosystems, "the most dramatic effect of earthworm invasion is the loss of the forest floor at an undisturbed forest site, which altered the location and nature of nutrient cycling activity in the soil profile. Invasion changed soil total carbon (C) and phosphorus (P) pools, carbon-nitrogen (C:N) ratios, the loss and distribution of different soil P fractions, and the distribution and function of roots and microbes." (Bohlen and Groffman 2004) Responses to invasion varied with site characteristics and earthworm species. The results of the study suggest that exotic earthworm invasion is a significant factor that will influence the structure and function of northern temperate forest ecosystems over the next few decades. Regional evaluations of these forests will need to consider the presence or absence of earthworms along with other important ecosystem drivers, such as pollution, climate, and underlying soil characteristics. (Bohlen and Groffman 2004)

Earthworm invasion has drastically changed the centerpiece of the hardwood forest ecosystem, the forest floor, which, for all practical purposes, is gone due to the disappearance of the O horizon. All of the processes that used to occur in the forest floor have been moved to deeper soil layers. Many of the organisms that used to live in the forest floor have lost their habitat and their food sources. Because the loose, spongy layer of litter is either gone or disappearing, organisms will either leave or die trying to find another habitat in which to live. (UMN, 2005)