Can Lumbricus terrestris be released in forest soils degraded by compaction? Preliminary results from laboratory and field experiments

Abstract

Compaction is an important and increasing threat for forest soils. In addition to preventive approaches, remediation solutions are needed. Among them, the release of anecic earthworms is thought to be a promising approach. However, most previous attempts in compacted forest soils failed to retrieve the introduced earthworms. To gain more insight on the feasibility of releasing Lumbricus terrestris adults, we performed both a laboratory and a field study. Under laboratory conditions, the L. terrestris behavior was assessed in repacked soil cores with increasing soil bulk density (1.3, 1.4, 1.5 and 1.6 g cm−3 for a silt-loam soil). We found that burrowing (burrow volume, diameter and maximal burrow depth) as well as casting and feeding behavior were significantly reduced (−95%, −50% and −65%, respectively) at the highest bulk density compared to the lowest. For the field study, we released L. terrestris in a 10-year old experimental forest site in which two factors were studied: soil compaction and liming. To prevent them from escaping, the earthworms were caged in PVC cylinders in compacted (or not) and limed (or not) plots. After six months, we assessed the burrowing behavior and litter consumption of the earthworms. L. terrestris showed a good survival rate (>52%), as assessed by surface activity, in all situations. Liming had no detectable effect whereas the increase in bulk density in compacted plots (from 1.29 to 1.36 g cm−3) led to a significant decrease in the burrow volume. This suggests that, when forced to do so, L. terrestris is able settle in compacted and acidic soils and then perform its functional role (burrow creation and litter burial).