Effects of earthworm invasion on morphology, carbon, and nitrogen of a forest soil

Soil samples were collected over 14 years from a sandy loam forest soil in northern Minnesota. During the study earthworm numbers increased from zero to 592 m(-2), the forest floor weight and thickness decreased by about 85%, and the E horizon was completely replaced by an A horizon. Development of the A horizon resulted in a increase of carbon and nitrogen concentrations but no changes in soil pH or C/N ratios in the surface mineral soil. Total soil carbon to a depth of 50 cm decreased at a rate of 0.6 Mg ha(-1) year(-1) during the study. Soil humus forms were mor at the beginning of the study and mull by the end. Site productivity, as inferred from herb weight or litterfall, was not affected by the increase in earthworm numbers.