| Summary: | Global climate models predict that the current trend of warming in the Arctic will continue over
the next century. The productivity of arctic plants is often limited by short growing seasons with relatively low temperatures such that a warmer climate could have large impacts on plants and plant communities. This study characterised alpine plant responses to changes in temperature at an alpine tundra site near Whitehorse, Yukon, Canada. I examined relationships between plant
productivity and natural temperature variations and assessed responses of plants exposed to an
experimental warming treatment. Non-destructive measurements of reproductive and growth
characteristics of four target species (Dryas octopetala, Lupinus arcticus, Polygonum viviparum,
and Salix arctica) were taken annually from 1999 to 2008. There was no significant effect of the
warming treatment (OTCs) on average daily mean temperatures as midday warming of up to 1.4
°C was largely offset by night time cooling in the OTCs. Vegetative measurements of target
species showed no significant responses to OTC treatments. However, peduncles of D.
octopetala and sections of P. viviparum inflorescences that produced bulbils were an average of 34.6 % and 64.7 % longer in OTCs than in controls, respectively. These treatment responses were likely due to plants responding to a factor other than temperature that was modified by the chamber. One vegetative and five reproductive characteristics were significantly related to annual variation in temperature. The summer of 2004 was exceptionally hot, and some species that did not respond to smaller fluctuations in temperature showed large changes in growth or reproduction in this year, perhaps indicating a non-linear response to temperature. Among the larger responses to the warm summer of 2004 was a shift in P. viviparum allocation from
predominantly asexual to sexual means of reproduction. Measurements of plant community
composition assessed at five-year intervals showed no differences in community composition
between experimental plots and controls, and changes in composition over the study period were
not uni-directional. In general, both individual plants and community composition were highly
resilient to observed variation in summer temperatures. Other factors, such as nutrient
availability, may be more important in determining plant responses to environmental change at this site than the direct effects of summer temperature variation.
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