Effects of whole-tree harvesting on nutrient accumulation in the subsequent forest stand: An examination of 6 Swedish long-term experiments

Whole-tree harvesting (WTH) is associated with increased nutrient losses compared to stem-only harvesting (SOH), potentially depleting the soil nutrient stocks and causing reduced growth and lower nutrient accumulation in biomass of the subsequent stand. This reduction in nutrient uptake, when expressed as a reduced net base cation uptake, can act as an “uptake brake”, that may lead to lower biological soil acidification. We used six Swedish long-term field experiments with randomized block design on WTH vs SOH performed in final fellings or thinnings to examine the long-term effects on nutrient status. The nutrient stocks in soil and biomass were examined 25 – 37 years after final felling, and 13–20 years after thinning. Following final felling, the total aboveground biomass, as well as stocks of N, P, and base cations (BC) in biomass, were significantly larger in SOH than WTH, but no such treatment differences were revealed after thinning. The differences in growth, not element concentrations, were in general the most important factor affecting rates of element accumulation in biomass. The “total stocks” of BC (salt exchangeable fraction in the soils plus aboveground biomass) were significantly larger following SOH than WTH after both final felling and thinning. The same pattern was found for the soil C stocks while only final felling exhibited significantly larger soil N stocks in SOH compared with WTH. These results support the hypotheses that WTH in final felling results in reduced tree growth in the subsequent forest stand, leading to lower nutrient uptake and thereby lower acidification pressure of the new stand compared to SOH. • Long-term effects of whole-tree versus stem-only harvest were compared in 6 trials • Lower forest biomass nutrient stocks after whole-tree harvesting in final felling • Reduced growth, not concentrations, was the main reason for lower nutrient stocks • Whole-tree harvest in thinnings reduced soil exchangeable base cation stocks • The whole-tree harvest nutrient “uptake brake” cause lower acidification pressure