Effects of ambient climate and three different warming treatments on fruit production in an alpine meadow community

Climate change is already having a major impact on alpine and arctic regions, and inter-annual variations in temperature are likely to increase. In a four-year study focusing on fruit production by an alpine plant community in northern Sweden, we applied three different warming regimes over the years. Treatments consisted of (a) a static level of warming with open-top chambers (OTC), (b) press warming, a yearly stepwise increases in warming, and (c) pulse warming, a single-year pulse event of higher warming. We analysed the relationship between fruit production and monthly temperatures during the budding period, fruiting period, and whole fruit production period, and the effect of winter and summer precipitation on fruit production. We found a significant effect of both year and treatment on total fruit production (highest in the press and lowest in the pulse treatment) and in the evergreen shrubs Cassiope tetragona (highest fruit production in press and lowest in pulse treatment) and Dryas octopetala (highest fruit production in press and pulse treatments), with large variations between treatments and years. Year, but not treatment, had a significant effect on deciduous shrubs and graminoids, both of which increased fruit production over the years, while forbs were negatively affected by the press treatment, but not year. Fruit production was influenced by ambient temperature during previous-year budding period, current-year fruiting period and the whole fruit production period. Minimum and average temperature were more important than maximum temperature. In general, increased precipitation was negatively correlated with fruit production. Summer precipitation decreased fruit production of D. octopetala, graminoids, deciduous shrubs, and total fruit production. Winter precipitation had a negative effect on fruit production of C. tetragona, evergreen shrubs, and total fruit production, while graminoids were positive affected. Similarly, the combined precipitation (winter and summer) had negative effect on fruit production of D. octopetala, deciduous and evergreen shrubs, graminoids, and total fruit production. In contrast, fruit production of forbs was not affected by precipitation. These results indicate that the predicted increased climate variability and increase in precipitation due to climate change may affect plant reproductive output and long-term community dynamics in alpine meadow communities.