The dripline is the guide measurement used to prevent unnecessary damage to trees during construction works. It is defined as the outermost circumference of the tree’s canopy, from which water drips onto the ground. The ‘dripline area’ is taken to include the soil and roots that lie within that circumference.
It is crucial for the stability and health of a tree that the dripline area is ‘off limits’ from any construction activity. It may be necessary to erect a fence around the dripline or, if possible, further out around groups of trees so as to prevent their roots from being damaged by construction plant, or by works such as excavation, soil compaction or consolidation. Fences should remain in place until all construction work is complete, including the final grading and smoothing of the site.
If work inside the dripline is unavoidable, only hand tools should be used. Where possible, tunnels should be excavated beneath the root system as opposed to trenching. Other measures that can be adopted to avoid undue damage include:
- Using porous paving materials such as brick or flagstone rather than concrete or asphalt.
- Not raising the grade of the soil inside the dripline by more than a few inches.
- Not lowering the grade of the soil inside the dripline by more than 2 inches.
- Not piling soil or construction materials inside the dripline, even for a short period of time.
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