SOIL SOLUTION CONCENTRATIONS ON 3 WHITE BIRCH SITES IN CENTRAL NEWFOUNDLAND FOLLOWING DIFFERENT HARVESTING INTENSITIES

Three white birch stands of differing site quality (good, intermediate , rich) in central Newfoundland were monitored using porous cup lysime ters to study changes in nutrient concentrations (NH4-N, NO3-N, PO4-P, K, Ca, Mg, pH) in the soil solution following stem only and whole tre e harvesting. Ammonium concentrations on the good and intermediate sit es were not greatly affected by cutting, but stem only (STO) harvestin g on the rich site led to increased concentrations that persisted for 3 y. Nitrate concentrations increased more on the intermediate than on the good site, but increases were smallest on the richest site. This was attributed to a combination of uptake by more vigorous advance reg eneration (mainly alders) on the rich site, as well as wetter soil con ditions that limited nitrification. Phosphorous concentrations were no t greatly affected by harvesting. Potassium concentrations increased i mmediately after harvesting as K leached from slash on the STO treatme nts, plant remains and the forest floor, and decreased as these source s were depleted. Vegetation uptake and leaching associated with moveme nt of NO3-N were also controlling mechanisms on some sites. Calcium an d Mg concentrations were correlated, and initially increased with harv esting, but on the richest two sites decreased below control stand lev els after whole tree harvesting (WTH) at the end of 3 y. Movement of C a and Mg was associated with NO3-N on sites where there was a signific ant increase in NO3-N concentrations following harvesting. Acidity dec reased on the good site, increased after STO, but decreased after WTH on the intermediate site, and increased after both intensities of harv esting on the rich site. Nutrient concentrations in the soil solution were generally higher when slash was retained in STO treatments rather than removed in WTH treatments. This was attributed to a combination of increased mineralisation beneath the slash, increased leaching from the slash, and decreased plant uptake. In general, the soil solution data suggest that harvesting effects last for no more than 3 y for mos t nutrients on these birch sites in Newfoundland, and that whole tree harvesting generally had less impact on nutrient concentrations than s tem only harvesting. However, this does not necessarily mean that net losses from sites were less with WTH, as this does not take into accou nt nutrient fluxes or nutrient removals in slash. (C) 1998 Elsevier Sc ience Ltd.