Sunburn in trees: causes, symptoms and protection

When we think of sunburn, we usually think of our skin. But did you know that trees can also get sunburned? Young trees, in particular, increasingly suffer from so-called bark burns during hot summers. What sounds harmless can impair a tree's health for years. With increasing heat waves and longer periods of drought, this issue is becoming ever more important in gardens and cities.

This article explains how trees get sunburned, which trees are particularly at risk, and how you can effectively protect your trees.

Content

• What is sunburn in trees?
• Why sunburn is becoming more common today
• What water and soil have to do with sunburn
• Which trees are particularly at risk?
• Recognizing sunburn: Typical symptoms
• Why damaged bark is problematic
• How can trees be protected from sunburn?
• Can a tree recover from sunburn?
• How to properly support damaged trees after sunburn
• What you shouldn't do when you have sunburn
• Can old sunburns heal?
• Sunburn or fungal infection – how can you tell the difference?

What is sunburn in trees?

Sunburn occurs when strong sunlight and high temperatures cause damage to the bark of a tree. The tissues directly beneath the bark are particularly affected. This is where the cambium, a thin growth layer responsible for the formation of new vascular tissues, is located.

If the bark is subjected to intense heat for an extended period, these sensitive areas can be damaged. As a result, the tissue dries out, the bark changes, and can later crack or peel off. The term "bark canker" aptly describes this process.

Why sunburn is becoming more common today

Many regions are now experiencing longer heat waves than they did a few decades ago. Other factors also play a role:

• higher average temperatures
• more days above 30 °C
• sealed surfaces in cities
• heated facades and streets
• prolonged periods of drought

Urban trees are particularly affected: asphalt, concrete, and building walls store heat and release it again at night, causing additional heat stress.

What water and soil have to do with sunburn

Healthy, well-watered trees usually cope well with intense sunlight. Problems arise when several stressors coincide, such as heat, drought, soil compaction, or suddenly exposed trunks. Sunburn is therefore often a sign that the tree is under overall stress. If you water your tree well and also occasionally tend to the soil, the risk of sunburn is much lower. In this article, you will learn more about... The relationship between water and soil for trees.

Which trees are particularly at risk?

Young trees

Young trees usually have thin and delicate bark. They haven't yet developed a thick outer layer that can serve as natural protection. Therefore, they are particularly sensitive to intense sunlight.

Smooth-barked tree species

Some tree species are naturally more susceptible to sunburn. These include beech, hornbeam, maple, linden, ash, and many fruit trees. Their relatively smooth bark offers less protection against intense heat.

Freestanding trees

Sometimes the problem only arises after changes to the location. For example, if a neighboring tree is felled or a dense group of trees is thinned out, a trunk may suddenly be exposed to direct sunlight. The bark is often not prepared for this.

Recognizing sunburn: Typical symptoms

The damage usually occurs on the south or southwest side of the trunk, i.e., where the sun's rays are strongest. Possible signs include:

• discolored bark areas
• light or reddish-brown spots
• sunken areas on the trunk
• bursting bark
• peeling pieces of bark
• exposed wood

Sometimes the damage only fully develops after weeks or months. Therefore, the cause is not always immediately identified.

Why damaged bark is problematic

The bark protects the tree from external influences. If it is damaged, it creates entry points for fungi, bacteria, pests, and wood-decaying organisms. The larger the damaged area, the more difficult it becomes for the tree to heal the wound.

How can trees be protected from sunburn?

Lime wash for the trunk

One proven method is a special Lime paint For trees. The light-colored surface reflects some of the sun's radiation. As a result, the bark heats up significantly less. This method has been used successfully for many years.

Reed mats and trunk protection

Reed mats, jute ribbons, or special trunk protection materials can also help. They shade the bark and reduce direct sunlight without hindering natural ventilation.

Make sure there is enough water

A well-nourished tree usually copes better with heat waves than one under drought stress. Water helps the tree maintain its natural processes. This includes transpiration through the leaves, which plays an important role in temperature regulation.

Therefore, it is particularly important to ensure an adequate water supply during prolonged periods of heat. Slow irrigation methods This ensures that the water penetrates deep into the root area and is available to the tree in the long term.

Can a tree recover from sunburn?

Many trees can heal minor damage on their own, healing with new tissue. Larger bark injuries, however, often require several years to regenerate. In some cases, the affected areas remain permanently visible. It is particularly important to avoid further stress and to ensure the tree receives adequate water during dry periods.

How to properly support damaged trees after sunburn

Even though damaged bark cannot be fully regenerated, many trees can compensate surprisingly well for sunburn damage. The key is to expose the tree to as little additional stress as possible in the months following the damage.

Therefore, pay particular attention to a consistent water supply, especially during prolonged dry periods. A layer of mulch protects the soil from further drying out and creates better conditions for earthworms, fungi, and other soil organisms. Active soil life supports the formation of new fine roots and helps the tree to efficiently absorb water and nutrients.

Additionally, biological support of the root zone can be beneficial. Vital bath It was specially developed to support weakened soils and trees after stressful situations such as heat, drought, or bark damage. The plant-based formula activates and nourishes soil life and promotes the formation of new root hairs. This allows for better absorption of water and nutrients, an important prerequisite for the regeneration of a damaged tree.

What you shouldn't do when you have sunburn

If the bark is already damaged, many people want to intervene as quickly as possible. However, not every measure helps the tree. Avoid, if possible,

• to forcibly remove loose pieces of bark,
• To close wounds with paints or varnishes,
• cut the trunk back severely
• to dig the soil deeply or
• to supply the tree with highly concentrated mineral fertilizers.

Many trees can heal minor damage on their own. It is more sensible to avoid further stress and support the tree's natural regeneration through a consistent water supply and good soil conditions.

Can old sunburns heal?

Sunburn damage rarely disappears completely. However, the tree attempts to heal the damaged area with new tissue. This process can take many years. As long as enough healthy tissue remains and no rot develops, many trees can still live for decades. It is important to provide the tree with sufficient water and maintain healthy soil.

Sunburn or fungal infection – how can you tell the difference?

Sunburn and fungal infections can look deceptively similar. Here are the most important differences:

Sunburn usually appears on the south or southwest side of the trunk and often occurs after prolonged periods of heat. Fungal diseases, on the other hand, often develop regardless of the cardinal direction and are frequently accompanied by fruiting bodies, discoloration, or rot.

If in doubt, it is advisable to observe the development of the affected area over several weeks. If the damage spreads or fungal fruiting bodies form, the tree should be examined by a specialist.