The answer is; have extensive root systems
Most grasses have ‘runner’ roots which are stems of the plant that grow horizontally below the soil surface. The buds on the stem are what gro to the leaves that emerge from the soil surface and we see as grass blades. Adventitious roots also grow downwards from this stem. Wildfires are not able to reach the stem and roots under the soil surface so grass can easily regrow even if the blades are destroyed.
