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LARSEN, KLAUS S.  University of Copenhagen, Denmark.

Snow insulates the soil, reduces soil temperature fluctuations and increases minimum temperatures (Brooks et al. 1997). Therefore, the distribution of snow is perhaps the single most important factor controlling the cold season carbon dioxide emissions in high-latitude ecosystems (Walker et al. 1999). Since global warming is predicted to increase the snow-cover in some arctic regions (Kattenberg et al. 1996), we need detailed information on snow-plant-soil interactions and on effects of changes in the snow regime in order to predict possible ecosystem responses to climate changes.

I will present preliminary results from a snow-fence experiment carried out in a subarctic dwarf shrub heath and a subarctic birch forest, the two dominating vegetation types of Northern Scandinavia (Sjörs 1971). The aim of the study was to a) quantify winter/early spring carbon dioxide emissions, to b) quantify pools and flows of carbon, nitrogen and phosphorus in soil and soil microbes, and to c) investigate the short-term effects of artificially increased snow-cover.

In March, before the initiation of snowmelt, snow-fences increased the snow depths significantly in the treated plots at the heath but not at the birch. Still, ecosystem respiration was higher in fenced plots compared to controls in both ecosystem types, by 157% and 77% in the heath and birch, respectively. The latter increase was probably due to earlier snow built-up in fenced plots. During the snowmelt period in April-May, snow depths were significantly higher in fenced plots until completion of snowmelt. However, no consistent differences in either ecosystem respiration or net ecosystem exchange between fenced and control plots were found during this period. Gross ecosystem production rates in subnivean vegetation were much higher than expected and were for the April-May period on average 39% lower in fenced plots than in controls due to increased snow-cover in fenced plots. Microbial biomass C, N and P were generally high in subnivean soils and decreased only as snowmelt was ending. Soil inorganic nitrogen and phosphorus concentrations were low throughout the experimental period, indicating a plant sink for nutrients concurrent with release from the microbial biomass.

Brooks, P. D., Schmidt, S. K., and Williams, M. W., 1997, Winter production of CO2 and N2O from alpine tundra – Environmental controls and relationship to inter-system C and N fluxes: Oecologia, v. 110, p. 403-413.

Kattenberg, A., Giorgi, F., Grassl, H., Meehl, G. A., Mitchell, F. B., Stouffer, R. J., Tokioka, T., Weaver, A. J., and Wigley, T. M. L., 1996, Climate models – Projections of future climate: Climate change 1995. The science of climate change, eds. J. T. Houghton et al., Cambridge University Press, Cambridge, p. 285-357.

Sjörs, H., 1971, Ekologisk botanik: Almqvist & Wiksell, Stockholm.

Walker, M. D., Walker, D. A., Welker, J. M., Arft, A. M., Bardsley, T., Brooks, P. D., Fahnestock, J. T., Jones, M. H., Losleben, M., Parsons, A. N., Seastedt, T. R., and Turner, P. L., 1999, Long-term experimental manipulation of winter snow regime and summer temperature in arctic and alpine tundra: Hydrological processes, v. 13, p. 2315-2330.

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