Effects of slash removal and stump harvesting on soil water chemistry in a clearcutting in SW Sweden

Abstract

Chemical properties of the soil water in a clearfelled Norway spruce forest in SW Sweden were monitored using lysimeters during a five‐year period. Measurements were made in plots treated as follows: (i) conventional harvest (CH), with slash and stumps remaining at the site, (ii) whole‐tree harvest (WHT), where only the slash was removed, and (iii) complete‐tree harvest (CTH), where both slash and stumps were harvested. Removal of slash from the clearcutting reduced concentrations of NO3 ‐, NH4 + and K+ in soil water below the rooting zone. In plots mechanically disturbed by stump harvesting, NH4 + concentrations increased strongly during the first year after felling. High levels were noted for two years, whereafter there was an additional two‐year period with elevated NO3 ‐ concentrations and reduced pH, indicating enhanced nitrification and NO3 ‐ leaching. The nitrate concentration drop coincided with a rapid expansion of the ground vegetation, mainly composed of Deschampsia flexuosa L. Trin., Carex pilulifera L. and Senecio spp. In slash‐covered plots, there was a rise in NO3 ‐concentrations about one year after felling. Within four years all major differences between treatments had disappeared. The possible use of whole‐tree harvesting for reducing NO3 ‐ losses from clearcuttings in areas receiving high atmospheric N loads is discussed.