Sitting, watching science occur

Sometimes science happens right in front of you. Sitting at my office desk, there is a pine tree not ten feet from the window. We have been having a steady rain for ten or fifteen hours now. We are about fifteen feet above ground. I notice there is foam forming between the pine bark plates.

Click to enlarge.

There it is, the white froth in the center of the tree, just about half way up. There is even more now, in other channels, fifteen minutes after I took the picture.

What is it? I find no studies per se but the consensus from various botanical sites is that it is a little discussed but not uncommon phenomenon (I am seeing plenty of other photos.) From Steve Pettis at The Georgia Gardener.

“My guess is that the foam is caused by the formation of a crude soap on the bark. During drought there is an accumulation of salts, acids and other particles from the air that coat the bark surface (soap is essentially salts and acids). When it rains, these mix with the water and go into solution. The froth (foam) is from the agitation of the mixture when it encounters a barrier (bark plates) during its flow toward the ground. Another example of this phenomenon happens on pavement after long dry periods following a rain. Car tires churn up frothy foam on the freshly wetted streets after a long drought.”

This comports with similar observations from others.

The suds are a chemical reaction of rain with pine sap and accumulated pollutants, facilitated by the physical turbulence as the effluvia runs down the bark channels.