Density and distribution of Dendrobaena octaedra (Lumbricidae) in aspen and pine forests in the Canadian Rocky Mountains (Alberta)

Dendrobaena octaedra (Savigny) and to a lesser extent Dendrodrilus rubidus (Savigny) recently colonized an aspen (Populus tremuloides Michx.) and pine (Pinus contorta Loud.) forest in the Rocky Mountains of southwest Alberta (Canada). Soil sampling along transects from a road into aspen and pine forests in 1992 showed that earthworm numbers decreased with distance from the road in both forests. A maximum of 3218 and 627 ind. m−2 were found in the aspen (August) and pine forest (June), respectively. Earthworm density in the aspen forest increased from May until August reaching a maximum of 2621 ind. m−2 and then decreased. Juveniles dominated and only a few adult specimens were present. Cocoon density varied between 2536 and 3699 m−2. Within the soil profile cocoons were almost exclusively located in H material. The vertical distribution of D. octaedra varied between sampling dates. From May to July earthworms preferentially colonized H material whereas in August and September most earthworms were found in F material. The data indicate that only few earthworms survive the harsh winter conditions. The rate of survival of cocoons was relatively high (average 48%), but viability depended on cocoon size.