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Global Forests -
Little Known or Interesting Factoids About Trees and Tree Physiology

Karen Rockoff is the primary contact 
Jim is in the hospital & will take calls through Karen.

Karen Rockoff is the only ISA certified
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                     Karen Rockoff  Arborist  - TDA Certified

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Lichens are organisms consisting of a fungus and a green or blue-green alga growing together in a mutually beneficial, symbiotic, relationship. Lichen is a combination of a fungus and a green or blue-green alga enclosed by the fungal hyphae.  The entire structure, called a thallus, is so different structurally from either of its partners that microscopic examination is necessary to distinguish the fungus and the alga. 
The fungus obtains food water and minerals from the air, the material it is growing on and from the alga, which manufactures food through photosynthesis and the alga receives some of its food and protection from the fungus. The alga provides carbohydrates and vitamins. Some blue-green algae fix nitrogen that is used by both the alga and the fungus. Nitrogen is also obtained from bird excrement, organic debris, or plant leachate.

Three forms of lichens exist, it may be flat, leafy, or branched and hairlike.- crustose (flat type of growth), foliose (leaf-like but with prostrate growth), and fruticose (bush-like and erect or hanging growth). The effect of lichens on trees is only slightly damaging.  All three forms occur on tree bark as well as on rocks, soil, and other substrates. Colors may range from white to gray, red, green, yellow, and black. Heavy lichen growth indicates poor tree growth as a result of some other cultural problem. Lichens can restrict gas exchange from the limb or twig and can restrict the amount of light received by a limb.

Materials used in the control of ball moss will kill the lichens for a short period. Regrowth usually occurs within the same year after the tree was sprayed. Chemical control of lichens is not currently recommended. This is due to two reasons, one, chemicals are currently not cleared by EPA and control has not been of long enough duration to warrant spraying. Rather, trees should be encouraged to develop a dense canopy which will shade out the lichen growth.


Although lichens grow on tree bark, they are not parasitic (disease-causing organisms), and do not harm trees. The fact that lichens grow rapidly when exposed to full sunlight may explain their profusion on dead trees. The one conclusion that may be drawn with certainty from lichens on trees is that the air nearby is relatively pure. Most lichens will not grow in a smoky or polluted atmosphere.
Photo Gallery:  Lichen on Trees - 

Sinclair, W.A., Lyon, H.H., and Johnson, W.T. 1987. Lichens, p. 506 In: Diseases of Trees and Shrubs. Comstock Publ. Assoc., Cornell U. Press, Ithaca, NY. 574 pp. Webster, John. 1980. Lecanorales, pp. 367-368 In: Introduction to Fungi. Cambridge University Press, Cambridge. 669 pp.

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