S1 File -

S1 Data and S2 Data: For both data files, the column headers are defined as follows. “OBJECTID” is a unique polygon identifier associated with the ArcGIS database. For the historical data, “densitycode” refers to the ordinal density categories, where the lowest number, 1, equals the lowest density “very thin” and so forth. “ChartNum” refers to the original chart number listed in Cameron et al 1915. For both files, “kelptype” refers to the dominant species composition, “kelpdensity” is kelp bed density in kg m-2 (see above), “aream2” is the polygon area in m2, “aream2_corr” is the discounted polygon area in m2 (according to density, see Section 1 above), and “location” is either California mainland or Channel Islands. “kelpwetmass”, “mt_C”, and “mt_CO2” are all calculated columns of each polygon’s total wet mass, dry C biomass, and CO2 equivalents; respectively, where the unit is mt = 1000 kg. For the contemporary file, “year” is the calendar year of the survey, “kelpbed” is the assigned bed number, and “class_name” is whether the surveyed kelp bed canopy was at the surface or just below (subsurface).
(ZIP)