The largest ecosystem on land is grassland with seasonal rainfall (dry part of the year). For this kind of environment to thrive, it needs large numbers of grazing animals because the grasses have evolved to need the trampling, the clearing out, the urine and defecation. Without that animal impact, grasslands turn into deserts.
The huge wild herds with their accompanying deadly predators are gone from most grasslands now. The land has been divided up into separate ownership. So now what can we do to prevent widespread desertification and the resulting immense release of CO2 into the atmosphere?