- Long-term effects of climate change on vegetation and carbon dynamics in peat bogs - 307 Journal of Vegetation Science 19: 307-320, 2008 doi: 10.3170/2008-8-18368, published online 5 March 2008 © IAVS; Opulus Press Uppsala. Long-term effects of climate change on vegetation and carbon dynamics in peat bogs Heijmans, Monique M.P.D. 1* ; Mauquoy, Dmitri 2,3 ; van Geel, Bas 2,4 & Berendse, Frank 1,5 1 Centre for Ecosystem Studies, Wageningen University and Research Centre, Droevendaalsesteeg 3a, NL-6708 PB Wageningen, The Netherlands; 2 Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Kruislaan 318, NL-1098 SM Amsterdam, The Netherlands; 3 Present address: Geography & Environment, University of Aberdeen, Elphinstone Road, Aberdeen, AB24 3UF, Scotland, UK; E-mail d.mauquoy@abdn.ac.uk; 4 E-mail vangeel@science.uva.nl; 5 E-mail frank.berendse@wur.nl; * Corresponding author; E-mail monique.heijmans@wur.nl Abstract Questions: What are the long-term effects of climate change on the plant species composition and carbon sequestration in peat bogs? Methods: We developed a bog ecosystem model that includes vegetation, carbon, nitrogen and water dynamics. Two groups of vascular plant species and three groups of Sphagnum spe- cies compete with each other for light and nitrogen. The model was tested by comparing the outcome with long-term historic vegetation changes in peat cores from Denmark and England. A climate scenario was used to analyse the future effects of atmospheric CO 2 , temperature and precipitation. Results: The main changes in the species composition since 1766 were simulated by the model. Simulations for a future warmer, and slightly wetter, climate with doubling CO 2 con- centration suggest that little will change in species composi- tion, due to the contrasting effects of increasing temperatures (favouring vascular plants) and CO 2 (favouring Sphagnum). Further analysis of the effects of temperature showed that simulated carbon sequestration is negatively related to vas- cular plant expansion. Model results show that increasing temperatures may still increase carbon accumulation at cool, low N deposition sites, but decrease carbon accumulation at high N deposition sites. Conclusions: Our results show that the effects of tempera- ture, precipitation, N-deposition and atmospheric CO 2 are not straightforward, but interactions between these components of global change exist. These interactions are the result of changes in vegetation composition. When analysing long-term effects of global change, vegetation changes should be taken into account and predictions should not be based on temperature increase alone. Keywords: Carbon cycling; Competition; Ecosystem model; Global change; NUCOM-BOG; Ombrotrophic peatland; Palaeoecology; Species effect; Sphagnum; Vegetation com- position. Abbreviations: LVM = Lille Vildmose; NUCOM-BOG = Nutrient cycling and competition model for bog ecosystems; WLM = Walton Moss. Introduction Peat bogs are important ecosystems in relation to climate change. Peat forming ombrotrophic bogs serve as important long-term sinks for atmospheric carbon dioxide (CO 2 ). Although peatlands cover only 2-3% of the global land surface, peat accumulation over thou- sands of years has resulted in a vast store of carbon of 450·10 15 g C (Gorham 1991), which is at least 20% of the global carbon store in terrestrial ecosystems. Climatic change could bring about changes in these ecosystems that would have important repercussions for global carbon cycling. Typical bog plant communities are comprised of peat mosses (Sphagnum) and associated vascular plants. Sphagnum species are the main peat- formers, because they decompose very slowly (Clymo & Hayward 1982). Carbon sequestration is expected to increase whenever Sphagnum expands at the expense of vascular plants and vice versa. Such vegetation changes not only affect carbon cycling, but also exchanges of heat and moisture (Thompson et al. 2004). Thus, changes in vegetation composition could feed back to the climate system through alterations in carbon storage and surface energy balance (McGuire et al. 2002). Therefore, it is of the utmost importance to know how these peatlands will respond to climate change. Another reason for studying peat bogs in relation to climate change is that the peat contains a natural archive of the history of the vegetation and carbon sequestra- tion. Based on 14 C dated sequences of plant remains, reconstructions of plant species composition through time can be made. Changes in species composition that have been observed in peat cores have been related to past changes in climate (Aaby 1976; Barber 1981; van Geel et al. 1996; Mauquoy et al. 2004). Therefore peat cores contain excellent material to study the long-term effects of historic climatic changes, such as the Little Ice Age.