Forest Ecology and Management 259 (2010) 2418–2425 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco Compositional changes of forest-floor vegetation in young stands of Norway spruce as an effect of repeated fertilisation Per-Ola Hedwall a,∗ , Annika Nordin b , Jörg Brunet a , Johan Bergh a a Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, 230 53 Alnarp, Sweden b Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden article info Article history: Received 11 January 2010 Received in revised form 18 March 2010 Accepted 22 March 2010 Keywords: Bryophytes Ellenberg indicator values Ground vegetation Nitrogen Picea abies RDA Vascular plants abstract Forestry practices that aim to increase biomass production may mitigate climate change through increased carbon sequestration and the potential of substituting fossil fuels with renewable biofuels. Fertilising young stands of Norway spruce in Sweden have shown to increase tree growth by more than 200%. Fertilisation, however, also has other effects on forest ecosystems. Here, we studied the response of the species composition of forest-floor vegetation to three different frequencies of fertilisation in young stands of Norway spruce. Fertiliser was applied every year, every second year or every third year. The total amount of N ranged from 425 kg ha -1 to 625 kg ha -1 , in combination with P, K, Ca, Mg, S, Mn, Zi, B and Cu. The largest effects of the fertilisation were found among bryophytes and lichens, which lost substantial cover. Unexpectedly, Deschampsia flexuosa, commonly known to be favoured by fertilisation, was negatively affected. Species that increased in frequency were Oxalis acetosella, Brachythecium sp. and Plagiothecium sp. Decreased availability of light, as an indirect effect of fertilisation through increased tree canopy cover, was found to be the most important factor behind the change in species composition of vascular plants. The total cover of bryophytes, however, did not show any significant response to the changes in canopy cover, indicating that the effects seen in this group may be a result of more direct effects of the fertiliser. Few significant differences were found between the two most intensive fertili- sation frequencies, although fertilisation every third year was often distinguished from both the control and the other fertilised treatments. Even though the effects at the stand level were substantial, the effects on biodiversity and function of ecosystems on a landscape or regional level need further investigation. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The demands of a growing world population, the need to miti- gate climate change with increased CO 2 uptake in forests and the subsequent substitution of fossil fuels with biofuels have recently led to increased interest in enhancing forest growth through fer- tilisation (Larsson et al., 2009). In Sweden, fertilisation has been a common practice in forestry since the 1960s, and a large body of work exists on the effects of fertilisation on wood production and the environment (Nohrstedt, 2001; Högbom and Jacobsson, 2002). Several studies have focused on changes of the forest-floor vegetation after fertilisation. Commonly recorded effects on vege- tation due to increased nitrogen levels are an increased abundance of grasses, such as Deschampsia flexuosa (Kellner and Redbo- Torstensson, 1995), to the detriment of dwarf-shrubs, such as ∗ Corresponding author. Tel.: +46 40415187; fax: +46 40462325. E-mail addresses: per-ola.hedwall@ess.slu.se (P.-O. Hedwall), annika.nordin@genfys.slu.se (A. Nordin), jorg.brunet@ess.slu.se (J. Brunet), johan.bergh@ess.slu.se (J. Bergh). Vaccinium myrtillus and V. vitis-idaea (Strengbom et al., 2001, 2002; Strengbom and Nordin, 2008), although a few studies have also shown increases of dwarf-shrubs (Kellner, 1993; Mäkipää, 1994). Bottom-layer species, bryophytes and lichens, normally decrease in cover after fertilisation (Strengbom et al., 2001; Strengbom and Nordin, 2008), with species replacement only occurring among bryophytes (Dirkse and Martakis, 1992). The effects of fertilisation and clear-cutting of the forest on forest-floor vegetation resemble each other to a large extent. Clear- cutting of boreal forest often results in compositional changes in the forest-floor vegetation. While early succession species like herbs and grasses increase, species typical of the mature forest, such as Vaccinium spp. which can be considered boreal keystone species, decrease in abundance (Bergstedt and Milberg, 2001). The cover of bryophytes often decreases (Jalonen and Vanha-Majamaa, 2001) and the proportion of drought resistant species increases (Hannerz and Hånell, 1997). Even though V. myrtillus is at its lowest abun- dance following stand-replacing disturbances like clear-cut, this period has been pointed out as important for the persistence of the species. Atlegrim and Sjöberg (1996) found that V. myrtillus had as high vegetative investment in clear-cut areas, as in closed forest, 0378-1127/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2010.03.018