Figure S1 Illustrative diagram showing how the LAI threshold-based DOY indices are computed from the simulated LAIs (panels a-g), MODIS LAI (h), and GLASS LAI (i). The diagram presents daily LAI in the year 2010, the LAI thresholds, and LAI threshold-based day of year (DOY) at 38.5°N, 82.5°W. We define the annual dynamical range of LAI as the difference between the annual minimum (min LAI) and maximum LAI (max LAI). We then calculate spring onset indicators based on the day of year LAI passes the 25%, 50%, and 75% thresholds of its annual dynamical range.