Stand productivity following whole-tree harvesting in early thinning of Scots pine stands in Sweden Gustaf Egnell a,⇑ , Kristina Ahnlund Ulvcrona b a Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd, SE-901 83 Umeå, Sweden b Department of Forest Biomaterials and Technology, Swedish University of Agricultural Sciences, Skogsmarksgränd, SE-901 83 Umeå, Sweden article info Article history: Received 27 October 2014 Received in revised form 15 December 2014 Accepted 17 December 2014 Keywords: Full tree harvest Energy harvest Nitrogen Nutrient availability Harvest intensity Bioenergy abstract Swedish energy policy and the introduction of targets concerning the proportion of renewable energy used within Europe have increased the demand for forest biomass that can be used for energy generation. This includes industrial forest residues, residues from logging operations, and whole trees harvested dur- ing early thinnings. However, the sustainability of utilizing the nutrient-rich parts of the trees, such as needles and twigs, may be questionable. It is therefore important to assess the impact of whole-tree har- vesting (WTH) in thinnings on the growth of the remaining trees in the stand, particularly in boreal for- ests where growth is normally limited by the availability of nutrients. Here we present data on 22 years of volume growth following WTH practiced in early thinning compared with the alternative, a late pre- commercial thinning, in which all of the biomass including the stem is left on site, from four Scots pine (Pinus sylvestris L.) dominated experimental sites in Sweden. WTH caused a statistically significant 4% growth reduction over the entire duration of the experiment. Analyses of volume growth at three different points in time following the experiments’ establishment suggested that this growth reduction occurred largely during the first growth period (0–8 years), when there was a significant negative growth effect. No statistically significant treatment effect on volume growth was detected for the second and third periods. The results for the two treatments are compared and discussed in relation to previously published findings concerning stand growth following WTH during thinning. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction The Swedish government has stated that renewable sources should provide 50% of the country’s energy requirements by 2020. This is one percent greater than the legally binding target of 49% specified by the EU Res directive (European Parliament, 2009). It is likely that Sweden will meet this target thanks to its forest biomass resources and adoption of policies favoring renew- able energy sources (Ericsson et al., 2004; Björheden, 2006). Most of the residual material produced by the forest industry is currently used for energy generation. Thus, the short-term demand for more forest biomass for energy generation has to be met by increasing the level of stemwood harvesting or by harvesting more of the available tree biomass. For forestry to be sustainable, long-term annual harvest levels must not exceed annual growth. Consequently, the growing demand for biomass in Sweden has pri- marily been met by harvesting a greater proportion of the trees’ biomass than the merchantable stemwood, i.e. branches, tops, and non-industrial wood. However, because the demand for bio- mass continues to increase, resources such as stumps and small- diameter trees are now being targeted as well (Egnell and Björheden, 2013). Small-diameter trees are already marketed in Finland (Heikkila et al., 2007), but have yet to be commercialized in Sweden due to environmental concerns and high procurement costs, which limit their profitability (Bergström et al., 2012; Lattimore et al., 2009). The current recommended practice in Swedish forestry is to perform pre-commercial thinning (PCT) when the trees are small (2–4 m) in order to reduce the cost of the operation and minimize the time to first thinning (Huuskonen and Hynynen, 2006). This approach has been used for several decades. Prior to 1993, the Swedish Forestry Act required forest owners to perform PCT. After 1993, PCT became optional. As a result, Swedish forests now con- tain a greater proportion of dense young stands with mean heights http://dx.doi.org/10.1016/j.foreco.2014.12.017 0378-1127/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd, SE-901 83 Umeå, Sweden. Tel.: +46 (0)90 786 84 55; fax: +46 (0)90 786 81 63. E-mail addresses: Gustaf.Egnell@slu.se (G. Egnell), Kristina.Ulvcrona@slu.se (K.A. Ulvcrona). Forest Ecology and Management 340 (2015) 40–45 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco