Answer: "Many types of fungi form a vast network of roots or so-called mycelium. This network grows underground, absorbing all the nutrients, and at some point, they use the stored up nutrients to grow above ground to spread their spores with the wind. So if you see a bunch of mushrooms clustered together, those things are all just like the tips of a giant iceberg growing beneath the ground. This network will grow outward as long as there are more nutrients to be found. The reason that they form these circles is that the mycelium dies off once there are no more nutrients in the soil. So while it grows outward, it dies off in the center. If the conditions are just right, it’ll form a nearly perfect circle in the process." 

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