Saturday, July 15, 2017

The Root System of a Tree

Tree roots are often regarded as vexatious – blocking drains, buckling footpaths and roads, etc. However, they do have some redeeming features.

The well known issue of road/gutter buckling
Tree roots help support the tree. They provide the tree with its nutrients from the soil, lower the water table and absorb run-off, prevent erosion and they work in a symbiotic relationship with other plants and fungi to produce a healthy ecosystem. Large roots act as storage for nutrients for when conditions are unfavourable.

A network of fine hairs that grow near the tip of the root absorb water. Although short-lived – they may only last a week or so – these fine hairs are the most important part, capturing water and nutrients from the soil and passing them into the tree via the roots.

The root tip itself is made up of some extra hard cells that are designed to do the tunnelling through the ground, then wear away and be replaced by a new set of cells, thus increasing the length of the root.

Some root systems can be extensive, covering hundreds of square metres and most root growth occurs close to the surface. This makes most tree roots susceptible to temperature changes, soil compaction and drought. (Most scholarly articles on the subject declare that soil compaction is the chief contributor to the poor health of a tree).

The shallow root section of a 30m eucalypt
Although some trees develop a tap root that goes deep into the ground, our native eucalypts generally have a shallow root system and this can make them vulnerable to blowing over in strong winds, especially when the ground is soft. Clusters or groups of eucalypts are usually more stable than lone trees as their mutually entwined root systems sometimes help support the group. The roots of some species will sometimes naturally graft with the roots of a neighbouring tree.

Strength, (stability), in numbers
The root system of many/all(?) eucalypts have swellings near the root crown, just above and below ground level called lignotubers. Lignotubers contain dormant buds that sprout if the tree is damaged by grazing or fire etc, so enabling the tree to survive.

The root zones of trees are rather special places and deserve to be treated with care and respect if we want healthy trees to be part of our urban environment.

PS: There might be numerous possible solutions to the age-old problem of tree roots and footpaths – anti-trip hinges between footpath segments, rubber and plastic footpaths, porous concrete and asphalt footpaths, interlocking pavers and bricks, suspended footpaths, gravel, structural soil, mulch, … (link).

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