Effects of biomass removal in thinnings and compensatory fertilization on exchangeable base cation pools in acid forest soils

Abstract

The effects of whole-tree harvesting and fertilization at first thinning on the exchangeable pools of base cations in the soil were examined on four sites five years after thinning. One site with Norway spruce ( Picea abies (L.) Karst.) is located in southwestern Sweden and three other sites with Scots pine ( Pinus sylvestris L.) are located in southeastern, south-central and northern Sweden. On all sites, the stands were thinned, and the following treatments were applied in a randomized block design ( n = 3): (i) stem-only harvest, logging residues left on site; (ii) whole-tree harvesting; (iii) whole-tree harvesting combined with compensatory fertilization (N–P–K were applied one year after thinning in the form of inorganic fertilizers, and the amounts were equal to the nutrient content of the harvested logging residues); (iv) stem-only harvesting in combination with N (pine sites) or NP (spruce site) fertilization (ammonium nitrate, 150 kg N ha −1, superphosphate, 30 kg P ha −1) and (v) whole-tree harvesting and nitrogen fertilization as in treatment (iv). There were no general treatment effects revealed from analysis across all sites. Effects of harvesting intensity were detected on two sites, indicating reduced pools of exchangeable K, Mg and Ca after whole-tree harvesting. The reductions were less pronounced than the effects observed in other studies from experiments with whole-tree harvesting at clear-felling of mature forests. Effects of application of nitrogen alone were more frequently observed than effects of harvesting of logging residues. In most cases, base cation pools were lower after N treatment than after other treatments, and this effect was probably due to exchange and translocation phenomena. However, Ca pools had increased after NP treatment on the spruce site due to high content of Ca in P fertilizer. No effect of compensatory fertilization with N–P–K was detected. A comparison between exchangeable nutrient pools before thinning and five years after indicated that K was generally lost from the soil profile.