The influence of soil compaction and the removal of organic matter on two native earthworms and soil properties in an oak-hickory forest

Earthworms may alter the physical, chemical, and biological properties of a forest soil ecosystem. Any physical manipulation of the soil ecosystem may , in turn, affect the activities and ecology of earthworms. The effects of removing organic matter (logs and forest litter) and severely compacting th e soil on native earthworm species were measured in a central USA hardwood region (oak-hickory) forest in the Missouri Ozarks (USA). Soils in this reg ion are characterized by a cherty residuum that is primarily of the Clarksv ille series (Loamy-skeletal, mixed, mesic Typic Paledults). Earthworms were collected from 0-15 cm depth each spring and fall for 2 years by handsorti ng, and densities were determined on a per meter square basis. Two native e arthworm species, Diplocardia ornata and Diplocardia smithii, were dominant on this site. Organic matter removal decreased the average individual biom ass of both species. However, both species responded differently to soil co mpaction. Soil compaction affected D. ornata adversely and D. smithii favor ably. This suggested that the degree of soil compaction was not as restrict ive with respect to D. smithii (2 mm diameter) as to D. ornata (5 mm diamet er). Moreover, the apparently improved soil environmental conditions result ing from the remaining organic matter in compacted soil enhanced the popula tion and growth of D. smithii. Sampling position on the landscape affected D. ornata but not D. smithii. Soil microbial biomass C and soil microbial b iomass N were decreased under soil compaction when the organic matter was r emoved. Other factors influencing the ecology and activity of these two spe cies will require further study.