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Climate change will cause large-scale plant migration. Seedling recruitment constitutes a bottleneck in the migration process but is itself climate-dependent. We tested the effect of warming on early establishment of three Arctic pioneer species, while holding other environmental variables constant. Seeds and bulbils were sown in artificial gaps in dry Arctic tundra and subjected to a 13-day heating of the soil surface by 2–8°C, simulating temperature increases ranging from the general summer warming to heat waves projected to occur more frequently with global warming. All species showed decreased establishment with increasing soil surface temperature. The short-term heat pulse decreased establishment of Polygonum viviparum and Saxifraga cernua, whereas establishment of Cerastium alpinum decreased with temperature due to more permanent natural variation in micro-climate. The treatment effects increased by the quadrat of the temperature increase. Warming and in particular heat waves may result in declining establishment of Arctic plants in dry tundra regions. [ABSTRACT FROM AUTHOR]

Extreme temperature events are projected to increase in frequency in a future climate. As successive extremes could occur more frequently, patches of vulnerable tundra vegetation were exposed to two consecutive heat waves (HWs) of 10 d each, with a 5-d recovery period in between. Surface temperatures during the HWs were increased approximately 6 degrees C using infrared irradiation sources. In three of the four target species (Pyrola grandiflora, Polygonum viviparum and Carex bigelowii), plant conditions improved upon the first exposure. Depending on species, leaf relative growth, leaf chlorophyll content or maximal photochemical efficiency was increased. In P. grandiflora the positive effects of the heat on the photosynthetic apparatus led to augmented net photosynthesis. By contrast, Salix arctica responded mainly negatively, indicating species-specific responses. During the second HW, leaf mortality suddenly increased, indicating that the heat stress induced by the extreme events lasted too long and negatively influenced the species resistance to high temperature. After the HWs, when plants were exposed to (low) ambient temperatures again, plant performance deteriorated further, indicating possible loss of cold resistance.