The Woodland Trust says oak trees are among the most loved trees in Britain, can live to over 1,000 years old, and have enormous value for our flora and fauna – supporting 2,300 species, with 326 species depending on the tree for survival, and 229 species rarely found on any other tree.
Specifically on their roots, the Woodland Trust says:
Oak roots are usually quite shallow, with most in the top 30cm of soil, and extend well beyond the tree's crown. The root system relies on a complex network of fungi to gather more nutrients beyond the tree's roots.
Exposed roots reflect this reality 🌳 pic.twitter.com/mjsGPpXq69
— The English Oak Project (@TheKentAcorn) December 30, 2022
But how far beyond a tree's crown do roots extend?
According to the Arboricultural Advisory and Information Service, in research undertaken for the Department of the Environment, tree root systems:
... are wide spreading, extending radially in any direction of distances often in excess of the tree’s height. Roots grow predominantly near the soil surface - over 90% of all roots, and virtually all the large structural supporting roots, are in the upper 60cm of soil. Soil disturbance within the rooting area should be avoided, as this can significantly affect tree stability and moisture uptake.
On depth:
Whilst genetic characteristics of a tree play some part in rooting pattern, soil conditions are of overriding importance. Thus, downward penetration of tree roots can be halted by excessive stoniness, ironpans, compact soil layers (especially compact clays), bedrock, poor aeration and high or perched water tables… Obstructions in the soil at shallow depths are common in the UK, and thus it is not surprising that a survey of root plates of wind thrown trees in southern England after the storms of 1987 and 1990 revealed that 44% of root plates were shallower than 1m, 95% were shallower than 2m and the deepest root plate was only 3m (cutler et al., 1990). This pattern accords well with the large amount of data available from excavations of root systems which indicate that average root depths are typically in the range of 1-2m.
On spread:
Root spread is not confined to the area delineated by a downward projection from the branch tips as has often been supposed. Excavation has revealed that roots can grow for a considerable distance beyond the branch spread; typically extending outwards for a distance equivalent to at least the tree’s height, and in some cases (particularly in infertile or compacted soils) up to 3 times tree height.
What are the implications of this? The research note puts this passage in bold:
Tree roots may extend radially a distance equivalent to at least the height of the tree and are located primarily in the upper 60cm of soil…. Thus, any soil disturbance within the rooting zone will damage tree roots and should be avoided.
Adding:
Within the rooting area the following should especially be avoided:-
- trenching, even a shallow (<150mm) trench
- soil compaction by movement of vehicles or storage of materials...
One year ago, we wrote another post about The roots of an oak tree…, saying:
Aggregate Industries’ proposed scheme to quarry Straitgate Farm would result in the loss of a large number of mature trees, according to the company’s own consultants, including two 200-year old oaks, Trees F and G.
The company's consultants had said:
Devon County Council Highways have confirmed that they would not accept a “no dig” construction, due to HGV vehicles that will be using the road to access the proposed development... [which] means that the works will potentially interfere with the root protection areas of Trees F, G and H and some of G15A as illustrated by Drawing R22/L/3-3-005 and it is likely they will be damaged by the development and need to be felled. 4.1
Days later, permission was granted to quarry Straitgate Farm, with Inspectors conditioning:
39 All existing trees, shrubs and hedgerows within the site and on its boundaries shall be retained and protected from damage during the process of extraction and subsequent restoration unless they are identified to be removed as part of the current phase or a succeeding phase of mineral working or restoration as set out in the approved plans.41 Outside the designated mineral working areas, trees shall not be felled, lopped or topped or have their roots damaged and hedgerows shall not be removed, thinned or cut back without the prior written consent of the Mineral Planning Authority.
Last year, East Devon District Council placed Tree Preservation Orders on Trees F and G saying:
The trees contribute to the amenity and character of the area and they are considered under threat from development and the impact of heavy machinery and vehicles.
How close are Aggregate Industries' construction works to trees F & G? This drawing couldn’t be clearer:
