It only happens with a couple of our trees.... Strangest thing ever and fun to see when it happens.
I've read somewhere that Tree Spit (stemflow) is really rain water which dissolves stuff from the treebark as it flows down the stem of the tree. This changes the surface tension of the water, so that when it drips down towards the base of the tree, air is introduced due to the turbulence of the water, and foam is formed because of the altered surface tension.
I believe it's not just on trees either! There's rock foam and even river foam - Sudbury River in MA has a lot of suds after a good rain.
Please visit this LINK if you would like to see only my art and not the other miscellaneous posts.
Thank you for visiting. Hope you came again!