The presence of lichens on healthy trees should be welcomed as likely positive indicators of lower levels of air pollution and a reasonably good quality of atmospheric conditions in the neighborhood. The three main body groupings are crustose (crust-like,), foliose (leaf-like, seen above), and fruticose (tube or beard-like strands). As bark ages, it changes in chemistry, texture, and ability to retain water, thereby influencing the type of lichen capable of living there. While they grow very slowly, i.e. These often inconspicuous, hardy, and adaptive plantlike organisms are composed of two fungi and a green alga. The lichens are not the cause for the condition of the stressed tree. Most lichen species grow best where there is sufficient light and moisture within a moderate temperature zone. Heavy infestations of lichens are most common on shrubs and trees in declining or poor health due to other factors. ALABAMA READY - Resources for Dealing with Hurricanes, Planting and Establishing Woody Landscape Plants, Lichens on Woody Trees and Shrubs, ANR-0857, Alabama Lichen identification most often is determined by the descriptive appearance, size, shape and color of the lichen body and the reproductive characteristics. Lichens may reproduce in a sexual, asexual, or vegetative manner. Tree lichens appear on many trees. Cooperative Extension System. Groerig, David J., Jim A. Chatfield, Sarah D. Ellis, Dr. Landon H. Rhodes, and Dr. Michael J. Boehm, (2009) "Lichens." The various chemicals produced by lichens are also identifying markers. Following recommended establishment, watering, and fertility practices will promote the development of a thick leaf canopy, which will inhibit lichen growth on twigs and limbs. So, no need to worry about lichen harming your tree, but you should reach out to a professional arborist if you have other concerns about tree health. The bark of a healthy tree continues to expand and slough off with the growth of the tree. Lichens are beautiful, especially when you view a lichen-drenched Douglas-fir or a colorful crust-covered cliff, and up close when viewed under a hand-lens or microscope. For more information, contact your county Extension office. School of Environmental and Biological Sciences, New Jersey Agricultural Experiment Station, Office of Continuing Professional Education, Tree, Shrub, and Flower Growing Publications, ohioline.osu.edu/hyg-fact/3000/pdf/HYG_3312_09.pdf, Report Accessibility Barrier or Provide Feedback Form, Rutgers, The State University of New Jersey, Executive Dean of Agriculture and Natural Resources, George H. Daniel, Rutgers Master Gardener, Somerset County, Nicholas Polanin, Agriculture and Natural Resources Agent, Somerset County.