Abstract
Spatial and temporal variations in soil conditions are expected to constrain earthworm-mediated benefits to crops and soil health in the Inland Pacific Northwest (IPNW). The objectives of this work were to describe the distribution and diversity of IPNW earthworms across regional and seasonal variation in soil conditions. In the springs of 2012-2013, 36 sites across the IPNW were sampled for earthworms and their density and diversity were measured. Aporrectodea trapezoides was the dominant species at all sites and a threshold for earthworm presence was observed at 330-370mm mean annual precipitation. A second study measured earthworm density and activity over 14 months at six sites in the annual cropping zone of the IPNW. Mean densities of 9 to 149 individuals m-2 over a 121-day active period were recorded. This work provides a starting point for determining the effects of earthworms on regional crop production and the potential impacts of climate change.