© Institute of Chartered Foresters, 2019. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com. 376 Forestry An International Journal of Forest Research Forestry 2020; 93, 376–388, doi:10.1093/forestry/cpz064 Advance Access publication 2 December 2019 Early growth of different tree species on agricultural land along a latitudinal transect in Sweden Lars Rytter 1, * and Reimo Lutter 2,3 1 The Forestry Research Institute of Sweden (Skogforsk), Ekebo 2250, SE-268 90 Svalöv, Sweden 2 Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Skogsmarksgränd 17, SE-901 83 Umeå, Sweden 3 Institute of Forestry and Rural Engineering, Estonian University of Life Sciences, Kreutzwaldi 5, EE-510 06 Tartu, Estonia *Corresponding author: E-mail: Lars.Rytter@skogforsk.se Received 23 March 2019 Fast-growing tree species will be an important tool in the future production of renewables and in substituting non-renewable fossil energy sources. Sweden, like other countries around the Baltic Sea, has large areas of abandoned farmland usable for biomass production, but knowledge of growth performance of tree species candidates is insufficient. An experiment was initiated where six potentially high-producing tree species were compared. The best available plant material for each species was used on five sites over latitudes 56–64 ◦ N in Sweden. Results from the first 8–9 years are reported. Short rotation coppice willow (Salix schwerinii Wolf × S. viminalis L., clone ‘Tora’) had the fastest initial growth and production in southern Sweden. Hybrid aspen (Populus tremula L. × P. tremuloides Michx.) and poplar (Populus spp., section Tacamahaca), grown as short rotation forest, grew well over all sites and showed the highest productivity at the two northern sites. Hybrid larch (Larix ×eurolepis Henry) displayed a high potential at the two most southerly sites, whilst silver birch (Betula pendula Roth) was a medium-producing species at all sites. Norway spruce (Picea abies (L.) Karst.) started slowly, and Siberian larch (L. sukaczewii Dylis) produced poorly at the two northern sites in the initial stage. All tree species followed existing height development curves for the respective species on a high site quality level. Currently, well-growing clones of Populus spp. indicated that a wider selection of tree species can be used at high latitudes under climate change. The study showed a high growth potential for most species on former agricultural lands. However, measures to reduce climate and biological damage must be included in future efforts. Introduction In order to counteract the current climate change (IPCC, 2014), carbon-neutral energy sources allowing fossil energy substitution will be of major importance. Woody biomass is today the single largest renewable energy source in the Nordic countries (Rytter et al., 2016), and the main supply of wood-based biofuels is com- ing from wood processing and harvest residues. Predictions show that woody biomass is likely to play an even more important role in the future, not only for energy supply but also for the new bioeconomic industries (Swedish Forest Agency, 2008; Nordfjell et al., 2010; Ollikainen, 2014; Rytter et al., 2015a). To increase the availability of woody biomass, other alternative supply systems, like fast-growing tree plantations on former agricultural land, are likely to be an option (Anonymous, 2006). The potential of afforestation of abandoned agricultural land to produce woody biomass has recently been emphasized for northern Europe (e.g. Rytter et al., 2016) and on the Swedish national level. Larsson et al. (2009) reported large opportunities for increasing wood and biomass resources through intensive forestry on both former agricultural land and forest land. Recent estimates show that 1.8–2.6 million ha of abandoned agricultural land is available for afforestation with fast-growing tree species in the Nordic and Baltic countries (Rytter et al., 2016). For Sweden, the available land area is 300 000–500 000 ha (Larsson et al., 2009). Although the area of available agricultural land constitutes less than 5 percent of total productive forest area in the region (Rytter et al., 2016), it could be an important future bioenergy area as the production potential of fertile agricultural soils is significantly higher than on forest land (Rytter et al., 2016; Mola-Yudego et al., 2017). If 5 percent of the available agricultural land in Nordic and Baltic countries should be afforested, an additional 8.5 Mm 3 of woody biomass could be produced annually (Mola-Yudego et al., 2017). Additional benefits with afforestation would be climate change mitigation by CO 2 sequestration (Rytter, 2012a; Lutter et al., 2016a). Rytter (2012a), for example, estimated that afforestation of 400, 000 ha with willows and poplars in Sweden could sequester 1.5 Tg C annually in woody biomass and 0.2 Tg C in the soil. The present experience in northern Europe also indicates increased biodiversity richness after afforestation on marginal lands (Weih, 2004; Randlane et al., 2017). Downloaded from https://academic.oup.com/forestry/article/93/3/376/5649146 by guest on 06 July 2022