Why does white foam sometimes form on trees when it rains?

Every other Friday on Morning Edition, the Outside/In team answers a question from a listener about the natural world.This week, Mihaela asks: “Every time it rains, there is a white foam forming at the base of the trees on our property… What is that?"

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Can anyone identify this foam on my Ash tree's trunk? : r

Foam is dripping from the trees after a day of rain : r/Weird

Foam is dripping from the trees after a day of rain : r/Weird

Foam is dripping from the trees after a day of rain : r/Weird

Foam is dripping from the trees after a day of rain : r/Weird

Why Are My Trees Blowing Bubbles?

Why do my pine trees foam when it's raining? - Quora

Foam is dripping from the trees after a day of rain : r/Weird

Foam is dripping from the trees after a day of rain : r/Weird