The Forestry Forum
General Forestry => Ask The Forester => Topic started by: davidlarson on March 15, 2009, 04:15:25 PM
Here in the mountains of western North Carolina the eastern white pine is a dominant forest tree. Sometimes after a heavy rain (it has been raining here most of this week-end) a white bubbly foam, like soap suds, will appear at the base of some of the pines, as though it is exuding from the bark. It disappears after the rain ends, and doesn't seem to appear during drier weather. I haven't seen any obvious holes in the bark that might suggest beetle infestation, but I'm not an expert. Does anyone have any idea what this might be? Should I worry about this, or is it just a harmless natural phenomenon? Thanks for any thoughts or opinions. Sorry I don't have any pictures. Probably I should enter the 21st century and get an appropriate camera.
David Larson
I've seen it here to, but not often.
I think all it is, is the rain water running down the tree trunk, much like water running down stream in a small creek.
Here and there you'll have bubbles.
No, this is definitely a white foam-like substance. I just saw it at the base of a white pine in my yard in NH after a very heavy rain, possibly more than 1.5".
It's the same type of mechanisms at work that creates foam in a stream or lake.
http://dec.alaska.gov/water/acwa/pdfs/fy05_arri_foamfactsheet.pdf
It's generally termed stemflow. As an example, stemflow from a 30 cm diameter hickory tree amounted to as much as 113 litres during a 2.5 cm rainfall. Stemflow serves to funnel a portion of the intercepted water into to soil at the base of the tree. It can result in increased leaching and podzolization of soil under the stem. (Pritchett and Fisher 1987, Properties and Management of Forest Soils)
I would guess that the rainwater is picking up impurities off the tree trunk and reacting with such things as atmospheric nitrogen, sulfur or potassium coming through the rain causing changes in surface tension. They are part or many particles up there in the air used to make precipitation, known as "condensation nuclei" in meteorology.
Jeff's paper gives further explanation.
I think the foam in streams is part of the process of forming conglomerates, when stream flow is reduced and that foam dries with calcium left behind to bind small stones with large ones. Nature's cement. ;D