What is the tree worth?

The trunk formula values a tree too big to replace with a nursery stock equivalent: take the cross-sectional area of the trunk, price it per square inch, then discount for species, condition and where it stands. Every one of those four inputs is a judgement, which is why an appraisal is signed by a person.

The four inputs, and how to rate them

InputWhat it meansHow to judge it
Unit costLocal replacement cost per square inch of trunkDerived regionally from nursery stock and installation
SpeciesSuitability and longevity in your regionA long-lived native rates high; a brittle short-lived species low
ConditionStructure, vigour, defectsThe rating a risk assessment would give it
LocationContribution to the site — shade, screening, placementA specimen shade tree rates high; a back-corner volunteer low

Sound

Unit cost is regional and is published in local appraisal guides rather than nationally. The default here is a placeholder to make the arithmetic visible — replace it with a local figure before you rely on the answer.

Why the number gets large fast

Because it is driven by trunk area, not diameter. Doubling DBH quadruples the base. A 12-inch tree and a 24-inch tree of the same species and condition are not two-to-one in value; they are closer to four-to-one. Measure yours properly with the DBH calculator — including the multi-stem rule, which materially changes the answer.

Three real uses

  • Deciding whether to save a tree

    Compare the value against a cabling install or a treatment programme. This is the most useful everyday use.

  • Understanding a municipal penalty

    Ordinances frequently assess unpermitted removal on appraised value or per inch — see the permit guide.

  • Supporting a claim

    Insurers and courts want a signed appraisal by a qualified arborist. This tool tells you whether the conversation is worth having.

For the first of those, put the number beside a cabling install and against the removal cost. Large specimen trees usually justify the support system comfortably.

Sources