Addition of 4–20 t ash ha−1 to a range of forest soils increased pH (KCl) by one to three units depending on soil C content, decreased exchangeable Al and H content, increased exchange sites (variable negative charges) and increased basic-cation levels. Ash addition increased respiration rates in all soils, especially in those with higher organic matter content. Addition of ash increased N mineralization rate and nitrification in most of the soils, although the magnitude of response was not clearly related to assessed soil properties.