Extended Data Fig. 4: Unusually warm weather in late winter, followed by extreme cold in early April, resulted in severe frost damage in the warmest enclosures at SPRUCE in 2016.
From: Ecosystem warming extends vegetation activity but heightens vulnerability to cold temperatures
a, Time series of daily mean air temperature, comparing plot 17 (+9.0 °C warming) and plot 19 (unheated enclosure), during the winter and spring of 2016. By the time the frost event occurred (grey shading), the daily mean temperature in plot 17 had been above freezing for over a month, but had repeatedly dropped below freezing in plot 19. b, Time series of 30-min air temperature—again comparing plot 17 and plot 19—leading up to and immediately following the frost event, which occurred on the morning of 9 April and again on 12 April. The thin red lines indicate the variability (maximum and minimum) across n = 5 temperature sensors in plot 17. c, Time series of daily GCC, the green chromatic coordinate, for Picea trees in plot 17 and plot 19. Arrows denote spring green-up dates (progressively larger arrows corresponding to 10%, 25% and 50% of seasonal amplitude) estimated from GCC. The pronounced decline in GCC in plot 17 following the frost event (grey shading) is readily apparent. Trees in plot 19 retained sufficient frost hardiness that they were undamaged, despite experiencing much colder temperatures. d, Brown frost-damaged Larix foliage in plot 17. e, Picea branches in plot 17, showing loss of most foliage from previous years, with green foliage from the 2015 flush retained only at branch tips. f, Picea branches with frost-damaged foliage from previous years, but healthy green foliage from the 2016 flush.
