Impacts of forest management on northern forest soils

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 influence not only the amount but also the balance of remaining plant-available nutrients in the long term. Canopy removal during harvesting influences soil temperature and moisture regimes. Physical effects of ground-based skidding may include soil structural change, influencing water retention and flow, and reducing aeration and root penetration. Higher soil temperatures in the daytime and during the growing season tend to result from the forest floor 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 denitrification and the reduction of manganese, iron and sulfate. Prescribed fire results in substantial nutrient losses through volatilization (notably of N and S) and, in some cases, fly-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 influenced 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 influenced by fire 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 acidification resulting from nitrification of fertilizer N can result in leaching of some heavy metal cations. (C) 2000 Elsevier Science B.V. All rights reserved.