BayCEER Workshop 2008

Longterm effects of recurrent soil freeze-thaw cycles differ strongly between vegetation types

Ongoing global warming will increase the recurrence of soil freeze-thaw cycles (FTC) in cool-temperate and other high-latitude regions, which were previously subject to prolonged periods of continuous winter soil frost. Freeze-thaw cycles (FTC) contribute to the release of nutrients in plant available form. However, knowledge on the effects of FTC on plant performance is scarce. Ultimately, the ability of plants to incorporate the released nutrients decides if the nutrient cycling remains closed or if losses from the ecosystem occur. Here, we analyze the effects of recurrent FTC on grassland and heath performance in a controlled field experiment in Central Europe (EVENT). Five FTC were created by buried heating wires in addition to three natural FTC in winter 2005/06. FTC significantly increased aboveground productivity and vegetation cover of grassland early in the first growing season. No significant reaction was found for heath within the first year after the manipulations. Without further manipulation, productivity of heath communities dropped significantly in the freeze-thaw treated plots in the second year, whereas no longer any effect was found in the grassland communities. Based on our findings, we propose that the fast and dynamic response of grassland helps to prevent nutrient leaching from the ecosystem. Heath systems appear to be more vulnerable to nutrient loss as they lack growth promotion in the first spring and suffer afterwards. The results show the high ecological importance of climate changes in winter, with the outcomes differing strongly between contrasting vegetation types.