Comment on “Changes in climatic water balance drive downhill shifts in plant species’ optimum elevations”

Crimmins et al. (Reports, 21 January 2011, p. 324) reported that plant species moved downhill between 1935 and 2005. They compared plot data for two time periods, ignoring that the modern plots were farther north than the historical plots. I contend that there is no support for a general downhill shift after correcting for this geographic bias.