Changes in the effects of whole-tree harvesting on soil chemistry during 10 years of stand development

Whole tree harvesting depletes soil nutrients and increases soil acidification more than conventional stem harvesting. This study examined whether this effect persists through stand development and to what extent forest growth and associated nutrient accumulation in biomass determined changes in soil chemistry over time. Changes in soil chemistry and nutrient capital in the forest floor and soil were determined over a period of 10 years (i.e., 15–25 years following harvesting) in two young stands of Scots pine and two young stands of Norway spruce in different parts of Sweden. Conventional harvesting of stems (CH) in these stands was compared with harvesting of stems and branches but with needles left on site (BSH), and whole tree harvesting (WTH). The effects of WTH on calcium and manganese concentrations in the forest floor and uppermost mineral soil (0–5 cm) were found to diminish over time, mainly due to more rapidly declining concentrations of these elements in CH and to some extent in BSH plots than in WTH plots. A similar pattern was found for total calcium and manganese concentrations in the forest floor and soil to 20 cm depth. The declining calcium and manganese concentrations in the forest floor were accompanied by more rapidly increasing levels of acidity and declining base saturation and effective cation exchange capacity in the forest floor in CH and BSH plots than in WTH plots. However, differences between harvesting treatments in aluminium concentration in the forest floor and calcium concentration in the deepest part of the mineral soil (10–20 cm) persisted over time. Differences in site yield capacity and expected nutrient accumulation in biomass among sites did not explain patterns of change in total amounts of nutrients in the forest floor and soil over time and the observed changes were generally small.

► Whole tree harvesting (WTH) and forest growth affect soil acidity and nutrient levels.
► We examined whether initial effects of WTH on soil chemistry persisted over time.
► Effects on calcium and manganese in the forest floor and topsoil declined over time.
► Effects on aluminum in humus and calcium in deep mineral soil persisted over time.
► Forest growth did not affect soil nutrient storage in a predictable way.