Population variation in cold hardiness of Pacific dogwood (Cornus nuttallii) Hrynkiewicz-Moczulski, Magdalena
Climatic variables and environmental conditions such as precipitation, sunlight, and soil are all important to the longevity of a species, but cold winter temperatures are one of the most limiting factors of species range. Pacific dogwood (Cornus nuttallii) is a beautiful tree found along most of the west coast of North America, from British Columbia to southern California. Despite its long range, previous studies have reported low local adaptation. In order to determine the population variation in cold hardiness, twigs were sampled in November 2008 and January 2009 from nine populations of Pacific dogwood planted in a common garden. Samples were analyzed for their Index of Injury at -18°C and -25°C, using the electrolyte leakage method (Hannerz et al., 1999). Statistical analyses showed that there was some population variation at -18°C in November, but no population variation at any of the other test temperatures or dates. This suggests that Pacific dogwood is not very locally adapted in its level of cold hardiness. This may be the result of high gene flow among populations due to seed dispersal by birds, as well as low genetic diversity caused by a population bottleneck during the Pleistocene glaciation. Therefore, this tree may not be well equipped to handle the environmental changes coming with climate change, but could perhaps be a candidate for facilitated migration.
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