Testing Hopkins’ Bioclimatic Law with PhenoCam data

Andrew D. Richardson, Koen Hufkens, Xiaolu Li, Toby R. Ault

Research output: Contribution to journalArticlepeer-review

33 Scopus citations


Premise of the Study: We investigated the spatial and temporal patterns of vegetation phenology with phenometrics derived from PhenoCam imagery. Specifically, we evaluated the Bioclimatic Law proposed by Hopkins, which relates phenological transitions to latitude, longitude, and elevation. Methods: “Green-up” and “green-down” dates—representing the start and end of the annual cycles of vegetation activity—were estimated from measures of canopy greenness calculated from digital repeat photography. We used data from 65 deciduous broadleaf (DB) forest sites, 18 evergreen needleleaf (EN) forest sites, and 21 grassland (GR) sites. Results: DB green-up dates were well correlated with mean annual temperature and varied along spatial gradients consistent with the Bioclimatic Law. Interannual variation in DB phenology was most strongly associated with temperature anomalies during a relatively narrow window of time. EN phenology was not well correlated with either climatic factors or spatial gradients, but similar to DB phenology, interannual variation was most closely associated with temperature anomalies. For GR sites, mean annual precipitation explained most of the spatial variation in the duration of vegetation activity, whereas both temperature and precipitation anomalies explained interannual variation in phenology. Discussion: PhenoCam data provide an objective and consistent means by which spatial and temporal patterns in vegetation phenology can be investigated.

Original languageEnglish (US)
Article numbere01228
JournalApplications in Plant Sciences
Issue number3
StatePublished - Mar 2019


  • Bioclimatic Law
  • PhenoCam
  • digital repeat photography
  • green chromatic coordinate
  • phenology
  • temperature sensitivity

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Plant Science


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