Answer: Mushrooms are the fruiting bodies of a fungus that grows beneath the soil. The underground portion are feeding on decaying wood such as buried lumber or possibly dead tree roots underground. Once the decayed material is thoroughly decomposed, the mushrooms will stop on their own. In the meantime, you can rake them away.
Based on your description, the mushrooms on the patio might be related to the tree that overhangs the patio. There might possibly be an unseen problem with the tree's roots dying back or having been damaged when the patio or deck was installed. If the mushrooms are occurring over a substantial area, and/or if the tree seems to be having problems/not thriving/not leafing out normally or has dead branches, you might want to consult with a professionally trained and certified arborist to make sure the tree is alright.
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