Effects of repeated whole-tree harvesting on soil properties and tree growth in a Norway spruce (Picea abies (L.) Karst.) stand

Increased demand for forest-derived biomass has resulted in changes in harvest intensities in Finland. Conventional stem-only harvest (SOH) has to some extent been replaced with whole-tree harvest (WTH). The latter involves a greater removal of nutrients from the forest ecosystem, as all the above ground biomass is exported from the site. This has raised concerns that WTH could result in large changes in the nutrient dynamics of a forest stand and could eventually lower its site productivity. The objective of this study was to assess the effects of repeated SOH and WTH on surface soil properties and stand growth in a fertile Norway spruce (Picea abies (L) Karst.) stand. The studied stand is part of a series of whole-tree thinning experiments established in Southern Finland. Ten years after the final harvest it was evident that repeated WTH had a decreasing effect on total C and N pools in the combined organic + mineral soil layer compared to the SOH treatment. The response of soil chemical properties to the treatments was more apparent in the mineral soil layer than in the organic layer. Treatment did not have a significant effect on pH or on the C/N-ratio of the soil. The results suggest that although the stand possesses significant pools of nutrients at present, WTH, if continued, could have long-term effects on site productivity. Harvesting intensity and fertilization had no effect on Norway spruce volume increment during 20 years before clear-felling. Ten years after final felling, no evidence was found that WTH had affected the growth of the new generation of planted Norway spruce seedlings. (C) 2013 Elsevier B.V. All rights reserved.