Table S2.
Fire season start (first quartile, Julian day), median discovery day (Julian day) and fire season length (IQR, in days) by ecoregion and averaged across the entire coterminous United States
| Ecoregion | Fire season start (Julian day) | Human advancement (d) | Median discovery day (Julian day) | Human advancement (d) | Fire season length (IQR, days) | Human expansion (d) | |||
| Human | Lightning | Human | Lightning | Human | Lightning | ||||
| Coterminous United States | 81 | 182 | 101 | 140 | 206 | 66 | 154 | 46 | 108 |
| Eastern Temperate Forests | 69 | 149 | 80 | 111 | 181 | 70 | 167 | 66 | 101 |
| Great Plains | 84 | 181 | 97 | 163 | 207 | 44 | 148 | 47 | 101 |
| North American Deserts | 129 | 187 | 58 | 178 | 207 | 29 | 92 | 40 | 52 |
| Temperate Sierras | 126 | 180 | 54 | 166 | 201 | 35 | 85 | 39 | 46 |
| Tropical Wet Forests | 64 | 153 | 89 | 107 | 175 | 68 | 98 | 52 | 46 |
| Mediterranean California | 161 | 201 | 40 | 198 | 226 | 28 | 85 | 45 | 40 |
| Northwestern Forested Mountains | 175 | 196 | 21 | 212 | 215 | 3 | 75 | 36 | 39 |
| Marine West Coast Forest | 184 | 194 | 10 | 218 | 217 | NA | 67 | 52 | 15 |
| Southern Semiarid Highlands | 124 | 173 | 49 | 151 | 192 | 41 | 55 | 41 | 14 |
| Northern Forests | 105 | 148 | 43 | 120 | 196 | 76 | 51 | 79 | NA |
Note that the national-scale tripling of fire season length by human ignitions is driven by earlier (spring) fires in eastern ecoregions coupled with later (fall) fires in western ecoregions.