Kruger National Park in South Africa. Åse Elin Langeland

On the arid African savanna, grasses are growing faster than they were a generation ago, boosted by rising levels of carbon dioxide from the burning of fossil fuels. That is the finding of a new study that warns that faster growth could fuel larger wildfires and alter the distribution of wildlife.

Since the dawn of the industrial age, the amount of carbon dioxide in the atmosphere has grown by half, which is helping to speed photosynthesis and cause many plants to grow faster. The phenomenon, known as “carbon fertilization,” has been well documented in forests , and some experts believe it may be responsible for the greening of drylands around the globe.

It was long assumed, however, that grasses on the African savanna gain little from the extra carbon dioxide, as they already employ a highly efficient form of photosynthesis. But researchers are now finding otherwise.…