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Grasses fuel most fires on Earth and strongly influence local fire behaviour through traits that determine how flammable they are. Therefore, grass communities that differ in their species and trait compositions give rise to significant spatial variation in savanna fire regimes across the world, which cannot be otherwise explained. Likewise, fire regimes are continuously modified by alterations to savanna grass community traits, through species introductions and climatic changes. However, current representation of grassy fuels in global fire models misses important variation and therefore limits predictive power. The inclusion of grass trait diversity in models, using remotely sensed trait proxies, for example, will greatly improve our ability to understand and project savanna fires and their roles in the Earth system. Most fires on Earth occur in savannas, but vary considerably in their extent, frequency, and intensity. These patterns cannot fully be explained by climate or land management. An important 'missing-piece' in explaining the variation in savanna fire regimes is the diversity of grasses that fuel fires and whose traits strongly influence fire behaviour. The major differences in savanna fire behaviour across continents may lie in the contrasting species and trait assemblages in savanna grass communities. Fire regimes change significantly when savanna grass communities or traits are altered by the introduction of invasive species and climatic changes. Improved representation of grass trait diversity in fire models will be essential for reliable forecasts of the behaviour and impacts of the majority of fires on Earth. [ABSTRACT FROM AUTHOR]