Could CO₂-induced changes to C₄ grass flammability aggravate savanna woody encroachment?

Fire plays an important role in maintaining the savanna tree-grass balance by limiting recruitment of heat-sensitive tree seedlings. However, fire behaviour may change under increasing CO2 concentrations, due to altered flammability grassy layer. Here, we determined effect predicted future and how it interacts with water-availability, on grass traits influential flammability, uncovered physiological mechanisms underpinning these responses. Using widespread C4 grass, Themeda triandra, as a model, found that improved water-use efficiency elevated (800 ppm) resulted larger (greater aboveground biomass), but wetter (higher moisture content) fuel load, cured at slower rate drought conditions. These changes were associated increased time ignition, reduced flaming times spread. We modelled national level (South Africa), finding large-scale reductions spread CO2, mitigating converse effects increases aridity, marginal fireline intensity. CO2-induced frequency, or intensity could have serious implications for vegetation dynamics, possibly exacerbating woody encroachment already seen ecosystems across world.