Is there evidence for a trade-off between cold tolerance and growth among North American willows?
It has been hypothesized that the range limits of woody plants are determined by a trade-off between freezing tolerance and growth rate, such that species with high freezing tolerance have low growth rates. However, willows (genus Salix) appear to be an exception to this pattern as they have high growth rates and high freezing tolerance. To determine whether there is evidence for this trade-off in willows, I compared the growth and freezing tolerance of twenty-eight willow species collected across North America. All species demonstrated greater freezing tolerance than expected from their geographic range, but the rate of their acclimation differed and could account for their distributions. There was also evidence that growth and plasticity varied with species ranges. These data suggest that there is a relationship between growth and cold tolerance in willows but further research is needed to determine the functional basis of this trade-off.
