We removed and sorted the Oi horizon to collect surface-dwelling earthworms, and used an electroshock extraction method to sample sub-surface earthworms (Satchell et al., 1955; Thielemann, 1986; Bohlen et al., 1995). Electroshocking probes were sets of eight steel rods (50 cm long × 6 mm diameter), installed in a 4 × 4 arrays at 6.25 cm apart. Eight-wire delivery cables were connected to a gasoline-powered generator (Honda EU, 2000i) at one end, and split at the other end where alligator clips were connected and attached to probes. We applied 120 V A.C. for 20 min, and collected all earthworms that surfaced. A 1 m2 buffer was placed around each subplot for subsequent sampling. Adult earthworms were identified to species, and juvenile earthworms were identified to genus according to Schwert (1990). Each specimen was measured field moist, and frozen at −80 °C until freeze-dried for archiving. Earthworm freeze-dried weights from the October 2008 collection were used to calculate a fresh-to-dry weight ratio and estimate species-specific earthworm biomass across plots for each sampling period.
