Red Bark Phenomenon

In the past five years an odd phenomenon has been observed on the bark of over twenty species of trees in New England — an intense reddish-orange coloration.  It’s been determined that this is due to the presence of a microscopic green algae (Chlorophyta), tentatively identified as belonging to the genus Trentepohlia.  A branching mat of thick-walled algal cells containing a bright orange-red pigment alters the color of the bark.

Red Bark Phenomenon is especially prevalent on White Pine, Eastern Hemlock, Red Oak and American Beech trees.  Affected trees appear to be of varying ages and are often, but not exclusively,observed near bodies of water, such as swamps and rivers. Frequently (as pictured) only one side of a tree is affected.

The exact conditions that promote this growth of algae are not known, but theories include climate change in the Northeast, in particular warming seasonal temperatures, increased precipitation punctuated by droughts, and more turbulent weather.  (Photo by Adeline Casali)

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