Hello Mr. ______,
Thanks for your inquiry about lichens on trees in Oregon. Lichens are among the most beautiful and valuable gifts of our climate and vegetation to those of us lucky enough to live in Oregon. As you've seen, they grow on trees; they also inhabit rocks and soils, and a few grow on less expected substrates, such as mosses.
Lichens have no specialized structures for absorbing substances from their environment. They have rhizines, which are little projections from their bases that adhere to surfaces on which they grow. Rhizines do not conduct water, minerals, or food substances. They just grow into tiny cracks in the bark, rock, or soil surface enough to anchor the lichen body. On the other hand, the roots of vascular plants actually conduct water through tubes formed by plant cells. In lichens and bryophytes, however, water movement occurs through cell-to-cell absorption only.
Lichens are formed by two organisms - a fungus and an alga. The fungus provides the shape, and a lichen species' name is the name of the fungus that shapes it. The algal cells grow in a layer near the top of the fungal structure. They photosynthesize - they manufacture food - for both the fungus and themselves.
Ecosystems are served by lichens in several ways. Bryophytes, which are mosses and similar-looking small green plants (liverworts and hornworts) perform many of the same functions. One important function is water absorption. During a rainstorm, lichens and bryophytes soak up a lot of water. Forest mosses can absorb at least three times their body weight in water. Far more water is retained in a system that includes lichens and bryophytes than in a similar system without them. Water is released slowly by the soaked-up lichens and bryophytes, rendering the ecosystem (forest, grassland, shrubland, temporary or permanent water body) humid for a long time after rain has stopped. Nutrients are retained and slowly released in this way as well. The alternative to this retention and slow release is fast runoff and thus loss of water and nutrients during precipitation events.
Lichens and bryophytes provide habitat for a large and intricate community of algae and invertebrate animals. These small organisms all take in water and nutrients in the courses of their life cycles. They, too, assist in holding water and nutrients for a longer period than if they were absent. They also break down complex molecules into small molecules during their various means of obtaining energy to fuel their metabolic processes. Plants require simple nutrient molecules for their metabolic processes. Because of nutrient cycling and breakdown by lichen- and bryophyte-dwelling organisms, more usable nutrient molecules are available to plants than would be available if the bark, soil, and rocks were barren.
A byproduct of the existence of lichen and bryophyte algae-invertebrate communities is that food for other animals is more plentiful than if these organisms were absent. For example, many bark-foraging birds, such as juncos, woodpeckers, nuthatches, and bushtits, eat arthropods that inhabit lichens and bryophytes or else arthropods that feed on other arthropods that inhabit them. In my own yard, I've noticed that these bark-foraging birds tend to spend more time foraging on trunks and branches covered with lichens and bryophytes than on bare bark.
OK, back to the organisms you've seen on trees in Oregon and on your own spruce: Some kinds of trees in western Oregon are good substrates for lichens, and they can have a pretty dense lichen growth on them. Your description makes me think of Oregon white oak, the common oak in this area. These oaks are good, strong trees built of dense, entwined wood cells. They can support a lot of weight beyond their own, so lichen and bryophyte growth is fine, even though it looks like a lot. Big-leaf maples would be in the same situation - they are strong and dense (although the cells aren't quite as intertwined as those of oaks) and can support lots of weight. The native trees and the native lichens and bryophytes have the advantage of having evolved together over the past several million years, so that trees with bark that lichens can hold on to will have evolved strength enough to support them (if they weren't that strong already). I suppose some non-native trees - ornamentals in urban plantings - could have some problems and break under the load, but compared to the weight of branches themselves, I don't think the lichens and bryophytes weigh that much, even when wet.
Conifer species usually have fewer lichen and bryophytes species growing on their bark. Conifer bark tends to chip off in little plates, whereas broadleaf tree bark often builds up into a thick layer. There ARE exceptions - cherry (we have two native species, and at least one non-native also grows in forests here.) has smooth bark that renews its outer layer periodically by peeling, and madrone (native), which also repeatedly exfoliates bark layers. Thus, these last two examples are two that are hardwoods but don't support large lichen and bryophyte communities, because they're too slippery.
Spruce trees usually do not have a lot of lichens growing on their bark; it's typical conifer bark that peels off in little scales. (I'm not intimately familiar with Colorado blue spruce, but I'm pretty sure it's much like the Engelmann spruce that grows right outside my back door.)
It is possible that you are seeing growths that are not lichens. For example, a virus infection will have symptoms much different than fluffy lichen or moss material on the outside of the plant. Virus symptoms are things like stunting, deformation, concentric ring-shaped spots, mottling, and yellowing. It is also possible that you are seeing crustose lichens -- these look as if they were painted onto the bark. They don't hurt the tree either.
To get a specialist to pass judgement on your problem, more information would be needed. For example, it would be good to know where you are located, for help in thinking about the abundance of lichen growth you could expect on your tree, and to know more about the appearance of the stuff you are removing from the bark. Better yet, you might try showing a sample to a county extension agent -- they should be able to help, or at least refer you to someone who can.
Best wishes,
Kathy M.