What Is Growing on My Tree's Bark? Gerrein Green Arborist

What Is Growing on My Tree’s Bark?

As winter sets in and trees lose their leaves, homeowners often start to notice irregularities on tree bark that might not have been as visible before. Questions like, “What are those frilly, blue-green, mossy-looking growths on my tree? Are they harming it?” are common during this time of year. If you’ve spotted something unusual growing on your tree, chances are you’re looking at lichens. While lichens may seem concerning, they are not harmful to your tree and are actually fascinating organisms with a unique role in nature. Let’s explore what lichens are, why they appear on trees, and whether or not you need to do anything about them.

What Are Lichens?

What Is Growing on My Tree’s Bark? Lichens are often mistaken for moss or other harmful organisms, but in reality, they are entirely different. Although they’re sometimes referred to as “non-vascular plants,” lichens are not plants at all. Instead, they are a symbiotic partnership between two separate organisms: a fungus and an alga (or sometimes cyanobacteria). Each organism benefits from the other in this mutually supportive relationship.

The Alga (or Cyanobacteria): This component of the lichen produces food through photosynthesis, much like plants do. The alga provides the energy needed for the lichen to survive.
The Fungus: The fungus offers structural support and protection, creating a safe environment for the alga. This partnership allows lichens to grow in a wide variety of environments, from tree bark to rocks, and even on soil.

This collaborative relationship makes lichens unique and complex. They are somewhat similar to air plants (epiphytes) that thrive in the humid climates of southern states like Florida, but lichens are even more remarkable in their ability to adapt and survive in diverse conditions.

Are Lichens Harmful to Trees?

What Is Growing on My Tree’s Bark? The short answer is no, lichens are not harmful to trees. They are not parasitic or pathogenic, meaning they don’t feed on the tree or cause it any direct harm. However, lichens are often found on trees that are already in poor condition, which can lead to the misconception that they are responsible for the tree’s decline. Here’s the truth about their relationship with trees:

Lichens Prefer Sunlight: Since lichens rely on photosynthesis to produce food, they thrive in areas with good sunlight. Trees with sparse canopies, which allow more sunlight to reach the trunk and branches, are more likely to have lichens growing on them. Sparse canopies are often a sign that a tree is under stress or in decline, which is why lichens are frequently associated with struggling trees.
Slow Growth Encourages Lichen Growth: Trees that are growing slowly due to environmental stress, disease, or other factors tend to accumulate more lichens on their bark. Healthy trees with normal or moderate growth rates typically shed lichens naturally as their bark expands and renews.
Lichens Are Not Parasites: Unlike harmful organisms such as fungi that cause diseases, lichens do not penetrate the tree’s vascular system or steal its nutrients. They simply use the tree’s surface as a substrate, or a place to live.

Why Are Lichens More Noticeable in Winter?

What Is Growing on My Tree’s Bark? During the winter months, deciduous trees lose their leaves, exposing the bark and making lichens more visible. This is often when homeowners first notice these growths and become concerned. However, lichens are present year-round and are not exclusive to the winter season.

Should You Remove Lichens?

It’s important to note that lichens should not be physically removed from the bark. Attempting to scrape off lichens can damage the tree’s protective bark and vascular system, potentially causing more harm than good. Instead, focus on addressing any underlying issues that might be causing your tree to decline, such as:

Biotic Factors: Insects or diseases could be affecting the tree’s health.
Abiotic Factors: Environmental stresses like poor soil, drought, or improper planting conditions might be contributing to slow growth.

If you’re concerned about the health of your tree, a professional tree health assessment can help identify the root cause of the problem and recommend appropriate treatments.

The Role of Lichens in the Ecosystem

Far from being harmful, lichens play a valuable role in the environment. Here are some reasons why lichens are important:

Air Quality Indicators: Lichens absorb everything in their environment, including pollutants. Because of this, they are often used as bioindicators to monitor air quality. The presence (or absence) of certain types of lichens can provide insights into pollution levels in the area.
Survival in Harsh Environments: Lichens are incredibly resilient and can survive in conditions where most other organisms cannot. They can endure dry climates, sunny locations, and even nutrient-poor substrates like bare rocks.
Photosynthesis and Oxygen Production: Like plants, lichens contribute to the ecosystem by converting carbon dioxide into oxygen through photosynthesis.
Biodiversity: Lichens support biodiversity by providing habitats and food sources for various insects and microorganisms.

Why Do Declining Trees Have More Lichens?

What Is Growing on My Tree’s Bark? As mentioned earlier, lichens tend to grow more abundantly on trees with sparse canopies or slow growth rates. This doesn’t mean that lichens are the cause of the tree’s decline. Instead, they are taking advantage of the conditions created by the tree’s weakened state. To address these issues, consider consulting an arborist who can evaluate the tree and recommend solutions, such as:

Pruning: Removing dead or damaged branches can improve the tree’s overall health.
Soil Amendments: Providing supplemental nutrients can help the tree recover from stress.
Pest and Disease Management: Identifying and treating any biotic factors affecting the tree can prevent further decline.

Learn More About Lichens

For those who want to dive deeper into the fascinating world of lichens, there are several excellent resources available:

University of Kentucky’s Lichen Guide: This guide provides detailed information and photos of various types of lichens. Visit: ppfs-gen-20.pdf (uky.edu).
U.S. Forest Service on Lichens: Explore more interesting facts about lichens and their ecological importance on the U.S. Forest Service website: Lichens – US Forest Service.

Trust Gerrein Green for Tree Health Assessments

If you’re unsure about what’s growing on your tree or concerned about its health, Gerrein Green is here to help. Our team of highly trained professionals includes the only licensed Board Certified Master Arborist in Northern Kentucky and Cincinnati’s East Side. We specialize in tree health assessments, pruning, and care to ensure your trees thrive year-round.

At Gerrein Green, we understand that every tree is unique. That’s why we evaluate each situation systematically, offering honest pricing and safe, effective methods based on years of expertise. Whether your tree needs treatment, pruning, or removal, you can trust us to deliver exceptional service with your satisfaction as our top priority.