Wednesday, 3 January 2018

Foaming Trees

We've recently experienced an extended period of dry weather followed by heavy rain over the past few days. Yesterday there were several trees in our yard which were foaming, which led to the question why? 

Some research has shown that the bark and leaves contain glycosylated alkaloids (or isoprenoids called saponins) which foam when wet. These alkaloids naturally build up during extended dry periods. They don't actually emerge from within the tree, but simply dissolve and wash off the leaves and bark during rain. When the water drips down towards the base of the tree, this primitive 'soap' then foams (due to the altered surface tension) as air is introduced. 

Tree foam happens in all types of trees and locations worldwide.

This foaming also occurs in other areas such as rocks (rock foam) and in rivers and oceans, where phosphates combine with water and air to produce foam.

Strangely enough many terrestrial orchids live at the base of local trees precisely because of the 'wetting agent' properties of the saponins that are released from the bark of trees in heavy rain.

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