Why do lichens grow on trees

In this way lichens are no different to many plants and in Europe the first observation of an allelopathic effect goes back to at least classical Rome, where Varro and Pliny the Elder noticed the inhibition of plant growth around walnut trees. A Finnish laboratory investigation deduced that compounds produced by several soil lichens in the genera Cladonia , Cetraria and Stereocaulon could have an inhibitory effect on pine and spruce seedlings.

As well as publishing their laboratory findings the researchers also included anecdotal evidence in the form of a photograph that showed an area once kept free of these lichens by a tethered reindeer. In that area there were now healthy saplings around a parent tree but there were no saplings in the lichen-rich area which had been beyond the reach of the reindeer. A Canadian study showed that exudates from the terrestrial lichen Cladonia stellaris inhibited spruce growth but that removal of the lichen mats had a much worse effect on spruce growth, by worsening soil temperatures and moisture levels.

This led to the conclusion that the negative effect was easily counterbalanced by the ameliorating effects that the lichen had on the soil. Lichen extracts have been tested on various vascular plants and a web and literature search revealed various further findings.

Here are a few, just to show that there is no simple answer to the question of what lichens do to vascular plants:. Often you'll see lichens growing with bryophytes, so the two are potential competitors and a variety of lichen-bryophyte interactions do occur.

Crustose lichens look like thin skins or simple washes of paint on the underlying soil, rock or wood. At first it would appear that such simple, two-dimensional growth forms could be easily overgrown by many bryophytes. In fact some crustose lichens are very effective at keeping bryophytes away, quite likely with chemical deterrents. Lichens produce a wide variety of chemical compounds, some of which have negative effects on bryophytes - acting to prevent spore germination or inhibiting protonemal or gametophytic growth.

There is a small number of lichens which are soft and gelatinous when moist, but which dry to a hard crust. When these are found growing amongst bryophytes the dry, crusty states could easily kill the embedded bryophytes by suffocation.

The lichen Baeomyces rufus can grow over bryophyte mats or cushions and kill them by depriving them of access to light.

After a few years the lichen itself dies, decays and bryophytes can re-colonize the area. However, the lichen has produced propagules from which fresh lichens can grow in the surrounding area and this cycle continues. The bad news is that if your tree is suddenly sporting a spot of lichen, your tree is probably already in decline. Lichen is rarely found on healthy, vigorous trees.

Lichen loves sunlight and moisture, so it is often found in sunny, wet spots. If your tree has had a sudden loss of leaves or a branch, that means more light can reach the surface where the lichen is. To reiterate: the lichen is in no way harming your tree, but the presence of lichen may point to an unhealthy or dying tree caused by other reasons, such as pests or disease.

Lichen often grows on trees that are already in decline, rather than on healthy trees. Surprisingly, lichen can actually be of benefit. In fact, scientists use lichen as a measure of air quality in different areas.

Lichen also converts carbon dioxide to oxygen and absorbs any pollutants that are in the area. Lichen has been used for dyes there are some very colorful types of lichen! No , lichen will not hurt your trees. Because of their structure and growth habit, lichen will grow on your tree but not into your tree. Lichen will grow on both healthy, vigorous trees and on older or declining trees. The health of a tree is not related to the appearance of lichen , although many people think lichens damage trees and associate lichen growth with a stressed or declining tree.

An older, declining tree may have a sparser crown or leaf and branch dieback, which means an increase in sunlight that reaches branch and trunk bark where lichen grows.

An older tree may also have more brittle and fissured bark which offers more places for lichen to attach to. Plus, an old tree may have stopped exfoliating its bark.

Another thing to remember is the slow rate at which lichen grows. If you absolutely must remove lichen, spray your branches with a gentle soapy solution. After wetting the lichen, you can use a natural-bristle scrub brush and gently exfoliate the lichen off.

You can wash off the residue with a stream of water from your garden hose. If your tree is in good health, you can prune off branches that have more lichen than is to your liking.

Learn more about types of pruning for your trees. This could include:. Since lichens need a lot of sunlight to thrive, a full-leafed and shady tree crown may be the best revenge. See how trees in Connecticut benefit from supplemental fertilization. In addition to it being an indicator of healthy air quality, lichen is a food source : animals, including squirrels and voles, will eat it; deer will gnaw at it in the winter, and some indigenous tribes in what is now New England would eat it as well when food was scarce.

Birds include lichen as nest-building insulation. There is also a long history of humans using lichen. For centuries, lichens have been used for textile dyes. In the U. These same extracts from lichen that have anti-bacterial properties are found today in toothpaste and deodorants. You may have lichen on you right now! However, we can evaluate and diagnose what is going on and give you a comprehensive treatment plan.

Things change quickly in CT when it comes to pests, weather events, and other things affecting your trees and landscape.