Beech with directional crown symptoms before a driveway excavation inside the root zone

• Zone size. The widely used convention is 1 foot of protected radius per inch of trunk diameter, i.e. 12 times DBH, with a minimum radius and adjustment for species, soil and existing roots. For 70 cm DBH: 70 x 0.12 = 8.4 m radius from the trunk centre.
• Where the work falls. The excavation at 3 m is well inside that radius. A 25 cm cut removes the uppermost soil layer, which is where the bulk of the fine roots and the structurally important lateral roots sit. Compaction by vehicles and a plate compactor compounds it: the roots that survive the cut are then suffocated.
• Area affected. The owner's figure of about 40% of the root zone is well past the roughly 25% encroachment that is usually treated as the limit before significant impact is expected, and past it on the side where the crown is already thin.
• Directional match. Crown symptoms on the west, bark discoloration on the west, excavation on the west. That correspondence is the strongest single clue in the case: either the site has already been disturbed, or the tree is already expressing a root problem on that side, or both.
• Conclusion. The design as drawn is not compatible with retaining this tree in a condition the owner would recognise as healthy. The zone calculation is the argument, not an opinion about beech.

These are two different questions and the report should keep them apart.

• Today. The crown is thinning and extension growth is short on one side, which is a decline symptom, not proof of imminent failure. Beech is not a species that commonly drops limbs or fails suddenly from partial root loss without visible trunk or root-plate signs. With solid-sounding wood at 1 m, no lean, no conks and no cracking, the current likelihood of failure is at most possible, and probably lower. The house is a significant target, so the current risk is not negligible, but it does not justify emergency action.
• Over the next 5 to 10 years. The excavation kills roots; killed roots decay; decayed roots stop anchoring. Add a driveway that concentrates water and traffic near the trunk, and the trajectory is a slow increase in the chance of whole-tree or large-limb failure during saturated, windy conditions. That is the risk the owner is actually buying, and it arrives after the contractor has been paid.
• The honest framing for the client. Today's rating is moderate at most; the rating in ten years, with the driveway in place as drawn, could be high, and it will be inherited along with the house. The decision is not whether the tree is safe now but whether the design that creates the future risk should be approved.

I would not approve the design as proposed. Options in order of preference:

1. Redesign the alignment so the excavated area stays outside the 8.4 m zone. On many lots a shifted driveway, a narrower surface or a different access point achieves this.
2. Avoid the cut. Use a no-dig construction: permeable paving or a geoweb on a granular base laid at existing grade, or a raised timber deck spanning the roots. Compaction and grade change, not paving as such, are the main killers.
3. If some encroachment is unavoidable, keep it under roughly 25% of the zone, require a written tree protection plan, install fencing at the zone boundary before machinery arrives, ban storage of materials and washout within the zone, and require that any root pruning be done by an arborist with sharp tools and clean cuts, with roots under about 3 cm left intact where possible.

Monitoring. An annual inspection with photographs from fixed points, checking crown density, extension growth, and any lean, cracking or conk formation, gives early warning of decline. It does not make the tree safer; it only tells you sooner that it is going. If the owner will not change the design and will not accept a declining tree next to the house, removing the tree before construction is the cleaner decision, and the client should see the cost comparison in writing.