Vegetation succession as affected by decreasing nitrogen deposition, soil characteristics and site management: A modelling approach G.W.W. Wamelink a, *, H.F. van Dobben a,1 , F. Berendse b a Alterra, Wageningen University and Research Centre, Droevendaalsesteeg 3a, P.O. Box 47, 6700 AA Wageningen, The Netherlands b Nature Conservation and Plant Ecology Group, Wageningen University, Bornesteeg 69, NL-6708 PD Wageningen, The Netherlands 1. Introduction High atmospheric deposition of sulphur and nitrogen has had an immense impact on vegetation composition and succession in the last century, at least in large parts of Western Europe and North America (Hogg et al., 1995; Lameire et al., 2000). Well-known examples are the succession of north-west European heathland dominated by Erica tetralix or Calluna vulgaris to monospecific stands of the grass Molinia caerulea (Berendse and Aerts, 1984; Aerts et al., 1990) and the change in species composition of the understory of forests (Van Dobben et al., 1999; Lameire et al., 2000). Simulation of the nutrient cycle and the competition between plant species can help to understand the processes behind these changes, and can also provide insight into the most effective strategy to reduce human impact. An important driver for vegetation succession is the accumulation of organic matter (Olff et al., 1997; Prach et al., 2001), which has a large impact on the soil and the plant community (Berendse et al., 1987; Knops et al., 2002), and even on the abundance of animal species (Olff et al., 1997; Van der Wal et al., 2000). In Western Europe vegetation succession in ‘natural’ areas is strongly affected by management (Bakker, 1989; Buckley et al., 1997). Management intensity ranges from extensive, e.g. the regulation of grazers in forests by hunting, to intensive, e.g. the mowing of hay meadows several times a year. In areas with high levels of nitrogen deposition, vegetation management is often used to remove nitrogen from the system, and thus to counteract the Forest Ecology and Management 258 (2009) 1762–1773 ARTICLE INFO Article history: Received 7 February 2008 Received in revised form 26 May 2009 Accepted 30 May 2009 Keywords: Vegetation management Ammonium deposition Pollution Vegetation structure Nitrogen cycle ABSTRACT After many years of increasing nitrogen deposition, the deposition rates are now decreasing. A major question is whether this will result in the expected positive effects on plant species diversity. Long-term experiments that investigate the effects of decreasing deposition are not available. Model simulations may yield insight into the possible effects of decreasing nitrogen deposition on the vegetation. Therefore we developed the vegetation succession model SUMO which is closely linked to the soil model SMART2. In SUMO, the biomass development of five functional plant types is simulated as a function of nitrogen availability, light interception and management. The model simulates the change in biomass distribution over functional types during the succession from almost bare soil via grassland or heathland to various forest types.The model was validated on three sites in The Netherlands and one site in the UK. The aboveground biomass of two grassland vegetation types was well simulated, as well as the aboveground biomass of heathlands during succession of sod removal. Some of the stages of forest succession were simulated less well, but the calculated biomass in the older stages agreed with measured values.To explore the long-term effect of a decrease in nitrogen deposition, we applied the model to a heathland and a pine stand. In the heathland a major change was predicted as a result of decreasing nitrogen deposition in combination with turf stripping. The dominance of grasses changed into a dominance of dwarf shrubs, whereas at continuing high levels of nitrogen deposition grasses remained dominant. In contrast, the simulations indicated only very small effects of a decreasing N deposition in pine forests. This difference is due to the removal of excess nitrogen by management (turf stripping) in the heathland, whereas the more extensive management in the forest hardly removes any nitrogen from the system. The main conclusion from these examples is that a decrease of nitrogen deposition may retard succession, and consequently increase biodiversity in heathland but probably not in forest. The effects of declining N deposition depend on the amount of N that is removed from the system as a consequence of the various management regimes. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Fax: +31 317424988. E-mail address: wieger.wamelink@wur.nl (G.W.W. Wamelink). 1 Fax: +31 317424988. Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco 0378-1127/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2009.05.043