Climate Change Impacts on Seedling Establishment for a Threatened Endemic Thistle, Cirsium pitcheri

A study was conducted to assess the effects of predicted climate change on seedling emergence, growth, and survival for the federally listed threatened species Cirsium pitcheri in the region proximal to Chicago, Illinois, U.S.A. Three geographically distant extant populations that could potentially serve as donors to re- introduced Illinois populations were tested to determine the influence of local adaptation on seed response to climate scenarios at two future time points. For all three populations, temperature was shown to be the most critical factor impacting future growth. All populations performed worst at the 2095 temperature for four measured growth metrics: length of longest adult leaf, number of adult leaves, dry shoot mass, and dry root mass. Growth performance at the 2095 conditions did not correlate with climate familiarity but did reflect the genetic diversity of the parent population. Predicted changes in average precipitation did not produce a significant effect on any growth metric, possibly reflecting a limitation in the study conditions. Seedling emergence and survival were tied to seed mass, a trait influenced by maternal effects and correlated with the level of inbreeding depression in the parent population. These results suggest managing populations to maintain high genetic diversity could be an important factor in tolerating temperature stress associated with climate change.