Many effects of forest management on northern soil environments are characteristic of other latitudes, as well. Nutrient
removals in harvested timber are substantial, and on some sites this may in¯uence not only the amount but also the balance of
remaining plant-available nutrients in the long term. Canopy removal during harvesting in¯uences soil temperature and
moisture regimes. Physical effects of ground-based skidding may include soil structural change, in¯uencing water retention
and ¯ow, and reducing aeration and root penetration. Higher soil temperatures in the daytime and during the growing season
tend to result from the forest ¯oor displacement and other disturbances which may result from harvesting and site preparation
activities. Impairment of soil gas exchange, due to management activities, can result in increased leaching of nutrient cations
where soil pH is not very low, as a consequence of carbonic acid formation. Impaired gas exchange also results in anoxic
microenvironments and may result in denitri®cation and the reduction of manganese, iron and sulfate. Prescribed ®re results in
substantial nutrient losses through volatilization (notably of N and S) and, in some cases, ¯y-ash losses. Slashburning yields
base oxides in the ash. Hydrolysis of these oxides results in increased soil pH and both, the magnitude and the duration of the
pH change are in¯uenced by soil-buffering capacity. Many of the remaining ash nutrients are soluble, plant-available, and
highly susceptible to leaching. However, increased pH and sorption after burning may limit availability of micronutrient
metals and phosphorus in the soil. Hydrologic behavior can be in¯uenced by ®re effects on soil hydrophobicity. Urea fertilizer
use can increase soil pH in the short run and lead to increased leaching of metals and biocides associated with dispersible
organic colloids. In the longer run, the soil acidi®cation resulting from nitri®cation of fertilizer N can result in leaching of
some heavy metal cations. # 2000 Elsevier Science B.V. All rights reserved.