title: Herbarium records are reliable sources of phenological change driven by climate and provide novel insights into species' phenological cueing mechanisms.
abstract: OBJECTIVE
  Climate change has resulted in major changes in the phenology of some species but not others. Long-term field observational records provide the best assessment of these changes, but geographic and taxonomic biases limit their utility. Plant specimens in herbaria have been hypothesized to provide a wealth of additional data for studying phenological responses to climatic change. However, no study to our knowledge has comprehensively addressed whether herbarium data are accurate measures of phenological response and thus applicable to addressing such questions.
  
  
  METHODS
  We compared flowering phenology determined from field observations (years 1852-1858, 1875, 1878-1908, 2003-2006, 2011-2013) and herbarium records (1852-2013) of 20 species from New England, United States.
  
  
  RESULTS
  Earliest flowering date estimated from herbarium records faithfully reflected field observations of first flowering date and substantially increased the sampling range across climatic conditions. Additionally, although most species demonstrated a response to interannual temperature variation, long-term temporal changes in phenological response were not detectable.
  
  
  CONCLUSIONS
  Our findings support the use of herbarium records for understanding plant phenological responses to changes in temperature, and also importantly establish a new use of herbarium collections: inferring primary phenological cueing mechanisms of individual species (e.g., temperature, winter chilling, photoperiod). These latter data are lacking from most investigations of phenological change, but are vital for understanding differential responses of individual species to ongoing climate change.
authors.affiliation: Department of Organismic and Evolutionary Biology and Harvard University Herbaria, Harvard University, Cambridge, Massachusetts, USA cdavis@oeb.harvard.edu.
authors.forename: Charles C
authors.initials: CC
authors.lastname: Davis
authors.affiliation: Department of Organismic and Evolutionary Biology and Harvard University Herbaria, Harvard University, Cambridge, Massachusetts, USA Harvard University Center for the Environment, Harvard University, Cambridge, Massachusetts, USA.
authors.forename: Charles G
authors.initials: CG
authors.lastname: Willis
authors.affiliation: Massachusetts Natural Heritage and Endangered Species Program, Division of Fisheries & Wildlife, Massachusetts, USA Department of Biology, Framingham State University, Framingham, Massachusetts, USA.
authors.forename: Bryan
authors.initials: B
authors.lastname: Connolly
authors.affiliation: Department of Organismic and Evolutionary Biology and Harvard University Herbaria, Harvard University, Cambridge, Massachusetts, USA.
authors.forename: Courtland
authors.initials: C
authors.lastname: Kelly
authors.affiliation: Harvard Forest, Harvard University, Petersham, Massachusetts, USA.
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Ellison
mesh_terms: D057231:Climate Change; D035264:Flowers / Q000254:growth & development*; D008404:Massachusetts; D063245:Plant Development; D012621:Seasons; D013045:Species Specificity; D013696:Temperature; D013997:Time Factors
keywords: climate change; climate variability; herbarium specimens; museum collections; phenology