Development of an Amynthas Agrestis (Goto and Hatai) Populationin a Sugar Maple (Acer Saccharum Marsh) Stand in the Champlain Valley, Vermont.

The invasive earthworm Amynthas agrestis is a recent arrival in Vermont sugar maple forests. The extent of its range in northern woodlands may depend on the length of the growing season, the frost hardiness of A. agrestis and the length of time for these earthworms to mature. We observed a field population of A. agrestis from April 1, 2011 to November 15 2011. The first hatchlings were observed soon after temperatures increased to 10 C in early April 2011. It took 90 days before the first mature worms were observed. The maximum population density was 167 individuals per m² observed just before the first mature worms were found. The last worms were observed in November. These were mostly large adults greater than 12 cm in length. The fresh earthworm biomass followed a concave quadratic function of growing degree days (base 10 C) but this function was modified by moisture conditions during the week preceding the sampling date. In September and October, small adults of less than 6 cm length were observed. We hypothesize that this was due to lower availability of litter resources caused by the fast consumption of litter by A. agrestis during the summer. Incidentally, no other species of earthworm was found in the A. agrestis invaded forest patch despite of the proximity of a large population of Lumbricus terrestris in an abutting area.