Everything You Ever Needed to Know About Lichens
Everything you ever needed to know about lichens
Round Rock Leader
Saturday, March 5, 2005
By Emsud Horozovic, City of Round Rock Forestry Manager
What is that funny looking blue green stuff growing on my tree? You've no doubt seen them, maybe even wondered about them. Found in most regions of the globe, lichens are probably the least understood and most long-lived life-forms around, often misidentified as a mutant moss or dehydrated liverwort. Lichens are curious little creatures seen growing like leathery lace on trees and boulders. They are equally at home on rocks or fence posts or even the surface of an old shingle.
What are lichens?
Lichens are an example of a symbiotic relationship between algae and certain fungi. They are capable of producing their own food. The green and blue alga (plural form, algae) is associated with the fungus. Lichen grows at a rate of about a half-inch per century on exposed rock surfaces. Although lichens are found in most areas of Texas, they are most noticeable in areas that have extended periods of high humidity. The alga, which must stay moist and get plenty of indirect sunlight, lies encased in a tough-textured envelope or pouch created by the fungus. In exchange for this damp, protected habitat, the alga manufactures sugars via photosynthesis for the fungus, which cannot produce food on its own.
Do they only grow on trees?
You can find these unusual symbionts growing almost anywhere: encrusting the ancient granite boulders of Enchanted Rock, blanketing the arched branches of an East Texas oak, or even dangling from a South Texas mesquite in a form known as "Old Man's Beard." A hike to the upper elevations of any West Texas mountain range heralds brilliant hues of canary yellow, sage green and tangerine orange, the hallmark colors of hardy lichens, splashed across faces of volcanic ridges and cliffs.
Lichens serve very useful functions
According to scientists involved in agriculture, medicine and natural products research, lichens make a bevy of potentially beneficial compounds not manufactured by higher plants or other fungi. For example, the fungal component of one species of lichens generates usnic acid, a chemical that is very toxic to plants, viruses and bacteria, and appears to have antihistamine (anti-allergic) effects as well. These substances (produced only when the fungi is associated with its chosen alga) are excreted on the surface of a lichen's threadlike hyphae, the tiny, root-like filaments that allow it to cling to a suitable surface.
Because of this, lichen by-products are relatively easy to harvest and may show us the way for developing new herbicides (for weed control) and medical treatments of several types.
But lichens have actually been making themselves useful in the lives of people for thousands of years. Though their fibrous flesh often tastes quite bitter, lichens probably help stave off starvation when food is scarce. Artisans also covet (even today) certain types of lichens for their purple, blue, and magenta dyes, pigments readily absorbed by wool and silk. Still other species of lichens can lend a hand with brewing and perfume distillation.
Look at two practical uses of lichen. The wool for the original Harris Tweed coats was dyed using materials from lichens. The spread of radioactive materials from Chernobyl was traced using lichens because they concentrated the radioactive contaminants in their parts, and the lichens were then eaten by large animals.
Lichens contribute to creating soil and improving soil quality. Over the eons, lichens crumble rock into usable soil. If left undisturbed, they also help hold soil together, cutting down on the damaging effects of wind and water erosion. And because certain species of lichens contain a type of photosynthetic bacteria (instead of an alga) able to capture or "fix" nitrogen from the air, lichens can sometimes improve soil's nutrient content, making a site more palatable for crops.
And when it comes to flourishing in a barren, unfriendly place, virtually nothing is as tough as a lichen. In fact, if it weren't for lichens, Iceland and Greenland would have little or no vegetation at all. Caribou, reindeer and moose populations would be decimated too, since certain species of lichens, low in protein but high in carbohydrates, provide their only winter food source. Smaller animals possibly depend on lichens for their winter water supplies, while some birds and small mammals, like flying squirrels, build nests with layers of leafy, well-insulating lichen fragments.
Lichens absorb samples of almost everything in the air, soil and water around them, both good and bad. In fact, if you ever questioned the quality of air where you live and work, trust lichens; they never lie. With no protective cuticle layer, lichens sponge up stuff they need (like nutrients and water) as well as lots of chemicals they really could do without, including lead, zinc, cadmium and a host of other heavy metal air pollutants. Because lichens are so vulnerable to these toxin's deleterious effects, ecologists faithfully monitor lichen colonies in both densely populated and unpopulated areas, sounding an alarm when they discover regions completely devoid of them.
Many experts think lichens were some of the first organisms to colonize land surfaces on the young earth. The root-like organs of lichens are called rhizines. The rhizines penetrate rocks and aid decomposition. Lichens also produce acids and other chemicals that break down rocks and other materials. The materials are also used to support growth of the lichens. In a sense, the rocks are long-term or very-slow-release fertilizers. The rock decomposition minerals start the formation of soils. As lichens die they add to the organic material to the soil.
Let’s get back to trees
Let’s get back to the purpose of this article. The effect of lichens on a tree are only slightly detrimental. Although they are not parasitic, studies suggest that lichens do have a slight negative effect. The main concern is that lichens give a tree an unkempt appearance. Presence of lichens is a good indicator of a thin tree canopy. This often leads homeowners to conclude that lichens are the cause and not the effect of thin foliage. The best control for lichens is to maintain the tree in good condition. This will ensure a dense canopy which will shade the limbs and reduce photosynthesis. Without photosynthesis, lichens are not able to manufacture food needed for growth and development.
Copper containing fungicides are suggested as possible controls for lichens. Applications of Kocide DF for the control of ball moss, have been observed to control lichens for a short period of time. Currently copper fungicides are not approved for lichen control. Because of their limited affect on a plant, chemical control is not suggested.
And besides, at the slow rate of growth and longevity, they’ll be here long enough to record our past—if air and water pollution doesn’t kill them first.
Portions of this article were provided by Derrel Johnson, Janet R. Edwards, and Dr. Alex Shigo.
Forestry Manager Emsud Horozovic