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Human vs. lightning fire niche relative to NPP and lightning density, with greatest resulting fire density represented by dark red. (A) Lightning fires occur in areas with high lightning-strike density. (B) Human fires expand the fire niche to include areas with low lightning-strike density as well as areas with high NPP. Graphs on the bottom and far right show histograms of NPP and lightning strikes, respectively, for human- and lightning-started fires.
