Earthworms may influence soil quality and productivity under various ecosystems during thawing conditions. Recently, field studies in the forest and agriculture ecosystems have examined the effect of soil physical manipulations on earthworm populations and species. The obvious effects of tillage and compaction have been documented in the forest and agriuclture ecosystems. Significant reductions of earthworms are seen in tilled plots and under severely compacted conditions. Greater populations are seen in no-tillage plots and under noncompaced conditions. However, during the natural conditions of freezing and thawing changes in earthworm populations and species may be affected. Dominant species include Aporrectodea trapezoides and Diplocardia spp. in a Mexico claypan soil. The claypan acts as a semipermeable barrier to water, nutrients, and earthworms and extends from 24-64 cm in depth. Under freezing and thawing conditions, it is important to understand the ecology of these earthworms. Generally, the populaitons are substantially reduced but speciation is relatively unchanged probably due to lateral movement away from the claypan. Additional controlled studies on the effect of thawing on species will be discussed.

D. Jordan
Soil and Atmospheric Sciences Dept.
Univ. of Missouri
Columbia, MO