Fig. 3: Characterisation of tree mortality at the landscape scale based on structural metrics and mortality stages of individual dead trees.

The left-hand map shows three metrics of dead trees in RGB colour space (referred to as 3-prong mortality map hereafter), i.e., count of dead trees per ha (Red), percentage of brown-stage mortality per ha (Green), and median of dead tree crown sizes per ha (Blue). All three bands are normalised to values between 0 and 1 using the 2nd and 98th percentile of all hectare grids in California as the minimum and maximum values, allowing to highlight of relative highs and lows within California. Separate maps for each of the three metrics are provided in Supplementary Fig. 9. Panels a–f are examples of six generic types of tree mortality, as characterised based on dead tree count (first character: H=high, L=low), % brown-stage mortality (second character) and dead tree crown size (third character): a HLL, b HLH, c LHL, d HHL, e LLH, f LHH. Each panel consists of four items. The top left item is a sample area from the 3-prong mortality map. The top right item shows individual dead trees detected within a one-hectare grid located at the centre of the sample area. The crown area of the dead tree is shown in grey. The red dot indicates brown-stage mortality. The dotted lines represent 30 × 30 m grids. The lower left and lower right panels show the true colour NAIP images corresponding to the upper left and upper right panels. The geolocation of each sample area is indicated by a cyan circle on the 3-prong map.