What's Growing On That Tree?

摘要

I am often asked about growths on tree trunks and branches. Tree owners wonder if the growth will affect the tree's health. While many things growing on trees are benign, some can be an indication of a serious condition.Orange, black, gray, green, crusted or leafy growth on the surface of tree trunks and branches are primitive plants called lichens. These develop when microorganisms (fungi and algae) form a symbiotic association beneficial to both. The fungus provides astable body for the lichen and the algae provide sugars for energy through photosynthesis. Lichens also occur on the surface of soil, rocks and logs and can help in their decomposition. Lichens on trees grow on the dead surface cells of the bark and dono harm to the tree. In fact, lichen growth indicates good air quality, since lichens are sensitive to air pollutants. In northern Minnesota, gray-green lichens with long hairlike strands (Usnea spp.) hang from tree branches and are used as nesting material by the northern parula warbler.