Understanding tree roots: structure, functions and importance for healthy trees

When people look at a tree, they usually only see what's above ground: the trunk, the branches, and the crown. But an important part of a tree's life remains hidden: underground lies a complex root system that supplies the tree with water and nutrients and anchors it in the soil. 

This article explains how tree roots are structured, what tasks they perform, and how you can use this knowledge to best support your tree. 

Key facts at a glance

• Tree roots supply the tree with water and nutrients.
• Most active fine roots are located in the upper 30 to 60 centimeters of the soil.
• A tree's root system can be significantly wider than its crown.
• Fine roots handle most of the water absorption.
  
• Soil compaction, drought and lack of oxygen can severely damage roots.
  
• A healthy soil life supports root development.
• Regular, slow watering helps trees build a stable root system.

Why tree roots are so important

Without a functioning root system, a tree can neither absorb enough water nor access the nutrients needed for growth, leaf formation and metabolism.

Furthermore, many trees store energy reserves in their roots. These reserves help the tree, for example, with bud break in spring or with regeneration after drought stress and damage. The health of a tree therefore depends directly on the health of its roots.

What are the functions of tree roots?

Water absorption

An important function of the roots is to absorb water from the soil. This water is transported via vascular tissue to the leaves. 
There, it is needed for photosynthesis and simultaneously evaporates from the leaf surfaces. This evaporation process creates a natural suction that constantly draws new water from the soil.

Nutrient absorption

In addition to water, roots absorb numerous nutrients. These include nitrogen, phosphorus, potassium, magnesium, calcium, and trace elements. 
These substances are essential for growth, cell formation and metabolic processes.

anchoring in the ground

The root system provides stability. It anchors the tree in the ground and protects it from being blown over by wind and storms.

Storage of reserve substances

Many tree species store sugars and other reserve substances in their roots. These stores serve as an energy reserve for times of low photosynthetic activity.

Cooperation with soil organisms

Roots are in constant exchange with billions of microorganisms. Their collaboration with [various microorganisms] is particularly well-known. Mycorrhizal fungi, which support the tree in absorbing water and nutrients.

Structure of a root system

A root system consists of different areas that perform different tasks.

• Main roots: Main roots form the basic framework of the root system. They primarily provide stability and transport water and nutrients to larger root areas.
• Lateral roots: Numerous lateral roots branch off from the main roots. They access additional soil areas and increase stability.
• Fine roots: Fine roots are particularly thin roots with a short lifespan. They are responsible for the majority of water and nutrient uptake. They are constantly being formed and also regularly die off. This creates a dynamic network that continuously adapts to the conditions in the soil.
• Root hairs: Microscopic root hairs are located on the fine roots. They greatly increase the absorption surface area and are crucial for the tree's supply of nutrients.

Shallow-rooted, deep-rooted and heart-rooted plants

Here is an overview of the different root systems in trees:

Shallow-rooted plants: 

Shallow-rooted trees develop their roots predominantly in the upper soil layers. Typical examples are spruce, birch, and willow. These trees are often more sensitive to drought and soil compaction.

Deep roots

Deep-rooted trees develop strong vertical roots that penetrate deep into the soil. Examples of deep-rooted trees include oak, pine, and walnut. These trees can access water reserves in deeper soil layers.

Heart root

Trees with a shallow root system combine both strategies. Their roots grow both deep and wide. Examples of shallow-rooted trees include linden, beech, and maple.

Root depth of a tree: Where are most of the roots located?

Many people imagine a tree's root system as a reflection of its crown. They assume that the roots reach a depth similar to the tree's height.

In reality, things are usually quite different. Most active fine roots are located in the top 30 to 60 centimeters of soil. There, they find sufficient oxygen, moisture, and organic matter. In deeper soil layers, the oxygen content is often lower. Therefore, the vital fine roots are predominantly concentrated in the upper soil layer.

In practical terms, this means that the most sensitive parts of a tree are often located directly beneath the turf. It is precisely there that drought, soil compaction, traffic, or intensive use have a particularly strong impact on the roots.

How far do tree roots reach?

Depending on the tree species and location, roots can grow far beyond the drip line of the crown. Often, the root system extends to one and a half to three times the crown diameter. This allows the tree to access additional sources of water and nutrients. For irrigation, this means that water is not only needed directly at the trunk. The outer areas of the root zone also play an important role.

Where does a tree absorb water?

Many people believe that water is primarily absorbed through the large roots. In fact, this task is mainly performed by the fine roots and root hairs.

The thick roots primarily serve for transport and stabilization. Actual water absorption occurs through millions of tiny structures in the soil. Therefore, a tree can suffer from water stress despite strong main roots if its fine roots are damaged.

What factors influence root growth?

• Soil type: Loose soils promote root development. Compacted soils hinder growth.
• Water availability: Both drought and waterlogging can impair root growth.
• Oxygen: Roots need oxygen to live. If the soil is permanently compacted or waterlogged, oxygen deficiency can occur.
• Temperature: Extreme heat or severe frost puts a strain on the roots.
• Soil life: Earthworms, microorganisms and fungi improve soil structure and promote root development.

Common damage to tree roots

soil compaction

Soil compaction is one of the most common causes of root damage. It is caused, for example, by:

• Vehicles
• construction sites
• frequent entry
• heavy machinery

Compacted soils They contain less oxygen and hinder root growth.

Dryness

Prolonged periods of drought can damage or kill fine roots.

waterlogging

Permanently wet soils displace oxygen from the soil and put a strain on the roots.

Damage caused by construction work

Roots are often damaged during digging, paving, or laying pipes.

Watering correctly: How does water effectively reach the root area?

Since most active fine roots are located in the upper soil layers, water should penetrate this area as slowly and evenly as possible. Brief, shallow watering is often ineffective. Some of the water evaporates, and some runs off the surface. A much better approach is... slow and penetrating irrigation.

This allows the water to seep deep into the root zone and be stored there. At the same time, the tree is stimulated to develop deeper roots and access larger areas of soil. Young trees, in particular, benefit from a continuous water supply in the first few years after planting.

Soil life, mycorrhiza and roots

Roots never work alone. They are part of a complex network of microorganisms, fungi, and soil animals. A particularly important role is played by the... mycorrhizaIn this process, soil fungi enter into a natural symbiosis with the roots. 
The fungal threads significantly increase the absorption area of ​​the roots and support the tree in its supply of water and nutrients.

Additionally, earthworms and other soil organisms promote the formation of a loose, well-aerated soil structure.

Mulch, compost and organic soil improvers such as Worm compost can help to strengthen this soil life in the long term.