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?"

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

Inside the Spittlebug's Bubble Home - The New York Times

Foaming Pine Trees & Heavy Rainfall on Christmas Day

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

Why Are My Trees Blowing Bubbles?

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

Douglas Fir Bugging You From San Juan Island

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

Soapy Trees? Sometimes Trees Need a Shower

Tree Foam

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

Foaming Pine Trees & Heavy Rainfall on Christmas Day

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

Rebecca Roy's Instagram, Twitter & Facebook on IDCrawl

Tree Soap – Sidewalk Nature