Infestations on trees, which species and how does a tree defend itself?

 

Tree damage: causes, consequences and defense mechanisms

 

Trees are crucial components of our ecosystems and provide a wide range of ecosystem services, but like all living organisms, trees are subject to various degradations that can threaten their health and survival.

These attacks can be caused by biotic factors, such as fungi, insects and other pathogens, or by abiotic factors, such as extreme weather conditions, pollution and mechanical damage.

In this article, we explore the different types of tree infestations, how these infestations work to attack or colonize trees, and the defense mechanisms that trees have developed to defend against such threats.

 

Types of damage to trees

Infestations by biotic factors

 

Biotic infestations include fungi, bacteria, viruses, insects and other plants (such as parasitic plants). These organisms can attack trees, causing disease or physical damage that can affect the health of the tree.

 

Fungal infestations

Fungi can infect various parts of the tree, including roots, trunks, branches and leaves. Examples include root rot, caused by fungi such as Armillaria, and leaf spot diseases.

 

Examples of some fungal infections

True honey fungus infestation (Armillaria mellea)

Fungi that infect the tree through the roots or damage at the base of the trunk and attack the cambium and cause it to die. Which leads to weakening and ultimately death of the tree.

Powdery mildew (Podosphaera spp., Uncinula spp.)

A superficial fungus that covers leaves with a white, mealy powder, which reduces photosynthesis.

Sphaeropsis sapinea

Is a fungal infection that causes young shoots to die, with symptoms such as browning (discoloration) and growth disorders of the needles and shoots.

Elm disease (Ophiostoma ulmi, Ophiostoma novo-ulmi)

A fungal disease that attacks the vascular system of elm trees, resulting in wilting and death of the tree.

Sweet chestnut canker (Cryphonectria parasitica)

Causes cankers on the trunk and branches of chestnut trees, which can ultimately lead to the death of the tree.

 

 

Insect eating

Insects can attack trees by boring into wood, eating leaves, or sucking sap. Certain beetles, such as the bark beetle, and caterpillars of various butterfly species are common culprits.

 

Examples of feeding infestations

Bark beetles (Scolytinae spp.)

Insects that dig galleries between the bark and the wood, where the cambium of the tree. In this way, the tree can become ringbarked, which affects the health of the tree and ultimately, in the event of complete ringbarking or excessive weakening, leading to death.

Oak processionary caterpillar (Thaumetopoea processionea)

The caterpillars of this moth mainly feed on the young leaves of native oaks, such as the pedunculate oak, which can lead to (partial) defoliation of the tree.

Oak splendor beetle (Agrilus biguttatus)

A beetle whose larvae attack the bark and sapwood of oaks by feeding on them, especially in weak oaks, often resulting in the death of the tree.

Aphids

Suck sap from the leaves and excrete a sticky substance (honeydew), which can lead to sooty mold on the leaves. And in the case of extreme damage, this can lead to the death of, for example, young plants or trees.

Gall mosquitoes

Insects that cause the formation of galls on leaves and branches, which can lead to reduced growth and vitality of the tree. As well as reduced aesthetic value.

 

 

Damages due to abiotic influences on trees

 

Abiotic factors are non-living factors that can cause stress or damage to trees.

These include extreme temperatures, drought, flooding, air pollution, soil pollution, and mechanical damage (for example by mowing, pruning or storms).

Examples of abiotic factors that influence infections

Drought

Prolonged periods without sufficient rainfall can lead to water stress, which limits growth and makes trees more susceptible to other damage. If the drought is too extreme and too long, cavitation occurs in the wood and the tree can suddenly die.

Wind damage

Strong winds can break branches, uproot the tree or damage the crown structure.

Salt damage

Using road salt near trees salinizes the soil, which leads to osmotic stress, where osmosis reverses and the soil withdraws water from the tree, causing it to dry out. Salt also damages the roots themselves, causing them to no longer perform their physiological functions.

Frost damage

Late frosts in spring can damage young shoots and blossoms, affecting growth and fruit set. In extreme cases, frost cracks can even occur in mature trees, which undermine the mechanical strength of the trunk.

Air pollution

Gases such as ozone, ammonia and sulfur dioxide can cause leaf damage and reduce the tree's photosynthetic efficiency. The deposition of these substances in the soil also deteriorates soil quality and soil life. This causes the tree to become stressed.

Note that the annual nitrogen deposition from the air on one hectare of land is already too much to speak of a naturally balanced soil. And this puts pressure on ectomycorrhiza-forming symbionts and thus entire forest resources.

 

 

How biotic pests attack or colonize trees

 

Fungal infestations

Fungi often enter through wounds or weak spots in the tree and spread through the vascular system, leading to disruption of water and nutrient transport.

 

Insect eating

Insects can cause physical damage by

• drilling in
• and eating living wood
• or consuming leaf tissue,

which reduces or stops the water and nutrient transport on the one hand and the photosynthetic capacity of the tree on the other.

 

 

Defense mechanisms of trees

 

 

Against fungal attacks

 

One of the most important defense mechanisms of trees against fungal attacks is the CODIT principle (Compartmentalization Of Decay In Trees).

When a tree is injured, it creates barriers to seal off the affected area (timber) and limit the spread of pathogens.

 

 

Against gluttony

 

Against insect damage and other feeding damage, trees can use physical barriers (such as thick bark) and chemical defenses (such as toxic compounds or repellents) to repel insects and herbivores.

 

 

Susceptibility to tree attacks

 

Trees become more susceptible to attack due to a combination of stressors, which can reduce their defensive capacity. Stressors include poor growing site conditions, extreme weather conditions, air and soil pollution, and inappropriate management (such as excessive pruning) and soil compaction causing oxygen depletion.

And weakened trees simply produce fewer toxic compounds or antibodies. This gives the insect colony more opportunity and allows it to multiply better.

For example, spruce spruce damage has been on the rise because the Norway spruce in our region does not have enough rainwater to remain in good condition. Due to the weakened condition, they produce less resin. The spruce tree can then freely drill holes in the bark of the Norway spruce. Without getting a load of syrup (resin) on him and without getting stuck. And even the lavens that were placed under the bark can afterwards freely leave the tree (to the next one), because neither the boreholes were filled with resin, nor could the resin dry out and form a hard barrier, so they remained trapped.

 

 

Conclusion

The ability of trees to defend themselves against attacks is crucial for their survival and the maintenance of healthy forests and urban green spaces. By better understanding the interactions between trees and their predators, managers and caretakers can develop more effective strategies for maintaining tree health and biodiversity.

 

 

If you would like to know more about whether your tree is affected, what the consequences are, and what actions or measures need to be taken, please Contact us about you tree to be inspected.