Figure 4: Correlation coefficient (r) and slope between the three indicators and respective seasonal temperature in North America.

(a,b) GSstart and preseason (30 days before the mean date of GSstart) temperature. (c, d) GPPmax and summer temperature (mean temperature in June-July-August). (e,f) GSend and preseason (30 days before the mean date of GSend) temperature. Maps were generated using MATLAB 2016a (http://www.mathworks.com/products/matlab/).