How to Run a Forest Inventory: A Practical Guide
A buyer looking at an unmeasured stand has to price the risk that it holds less than it appears to — so they price defensively. Remove that uncertainty and the offer improves.
Growers consistently find a proper inventory is recovered several times over in the improved offer. It is the cheapest fully-recoverable mistake in forestry.
What Separates an Inventory From a Guess
- Plots are placed systematically, not where it is convenient to walk.
- Every tree in the plot is measured, including the poor ones.
- The method is written down so a buyer can verify it rather than doubt it.
- Volume is reported by grade, because price is set by grade, not by total cubic metres.
Walking the block and estimating fails all four. The trees you can reach easily are not a random sample, and stands are patchy — better on the mid-slope, worse on the ridge.
Plot Design
| Type | How it works | Best for |
|---|---|---|
| Fixed-area circular | A circle of set radius; measure every tree inside | Most plantations. Simple, robust, easy to check |
| Fixed-area rectangular | A strip or square of set dimensions | Row-planted stands; easy to lay along rows |
| Variable radius (prism / relascope) | Trees counted by angle gauge; larger trees counted from further | Fast basal-area estimation; needs training |
| Complete enumeration | Measure every tree in the stand | Small or very high-value blocks only |
Common circular plot sizes are 0.01 ha (radius 5.64m), 0.02 ha (7.98m) and 0.05 ha (12.62m). Smaller plots need more of them; larger plots take longer each. For dense plantation, 0.01–0.02 ha is usually practical.
Laying plots out honestly
- Use a grid or transect with a fixed interval, and take whatever falls where it falls.
- Do not move a plot because it landed on a bad patch. That is the single most common way inventories become dishonest, and it is usually unconscious.
- Include the edges and the gaps. They are part of the stand.
- Record the plot centre with GPS so anyone can re-measure it.
How Many Plots?
Enough that the answer is stable, which depends on how variable the stand is and how much precision you need.
| Purpose | Precision needed | Sampling effort |
|---|---|---|
| Rough planning estimate | Low | Light |
| Management planning | Moderate | Moderate |
| Timber sale | High | Heavier — the buyer will scrutinise it |
| Bank security / transaction | Highest | Heaviest, and methodology stated in full |
A practical rule: keep adding plots until the running mean stops moving materially. If your estimate is still shifting after each new plot, you have not sampled enough. Uniform plantations stabilise quickly; patchy natural stands do not.
Selling, financing or valuing? That needs an inventory a buyer can check.
What to Measure in Each Plot
- Diameter at breast height (DBH) on every tree — 1.3m above ground, uphill side on a slope. Two readings at right angles, averaged.
- Height on a subsample — typically enough trees across the diameter range to build a height-diameter relationship, rather than every tree.
- Merchantable height to the minimum usable top diameter, not total height.
- Form and defect — straightness, forking, damage, disease. This is what turns volume into grade.
- Stem count, including dead and missing, so stocking is honest.
- Plot location and slope, for the record and for any re-measurement.
From Plots to Stand
- 1. Volume per tree — basal area × merchantable height × form factor, or a local volume equation if one exists for your species.
- 2. Volume per plot — sum the trees in the plot.
- 3. Volume per hectare — plot volume ÷ plot area in hectares.
- 4. Stand volume — mean per-hectare volume across all plots × net stocked area.
- 5. Break it down by grade, because that is what determines price.
Use net stocked area, not title area. Deduct firebreaks, roads, gaps and unplanted ground. Multiplying a per-hectare figure by the title acreage is a classic way to overstate a stand by 10–20%.
Reporting It Credibly
A report a buyer will accept states:
- Plot design, size and layout method, with the sampling interval
- Number of plots and total sampled area as a percentage of the stand
- What was measured and to what conventions — over bark or under bark, minimum top diameter
- Volume equation or form factor used, and its source
- Net stocked area and how it was derived
- Results by compartment and by grade, not one aggregate number
- An honest statement of precision and its limits
- Plot coordinates so the work can be checked
That last point is what makes an inventory persuasive. A number anyone can verify is worth far more than a number they have to trust.
Frequently Asked Questions
What is a forest inventory?
A systematic measurement of a forest stand using sample plots laid out to a design, from which volume, stocking and grade distribution are calculated for the whole stand.
It differs from an estimate in four ways: plots are placed systematically rather than conveniently, every tree in each plot is measured, the method is written down, and volume is reported by grade.
How many sample plots do I need?
Enough that the running mean stops moving materially as you add plots. Uniform plantations stabilise quickly; patchy stands need more.
The purpose sets the standard: a rough planning estimate needs far less than an inventory supporting a timber sale or bank security, where the buyer or lender will scrutinise the method.
What size should sample plots be?
Common circular plot sizes are 0.01 ha (5.64m radius), 0.02 ha (7.98m) and 0.05 ha (12.62m). For dense plantation, 0.01–0.02 ha is usually practical.
Smaller plots mean you need more of them; larger plots take longer each. The total sampled area matters more than the individual plot size.
Can I move a plot if it lands on a bad patch?
No — and this is the single most common way inventories become dishonest, usually without anyone intending it.
Take whatever falls where the grid puts it, including gaps and edges. Moving plots off poor ground systematically overstates the stand.
Do I measure the height of every tree?
Usually not. Measure DBH on every tree in the plot, and height on a subsample spanning the diameter range, then build a height-diameter relationship for the stand.
Measure merchantable height to the minimum usable top diameter rather than total height — the tip of the tree is not saleable.
Is an inventory worth the cost for a small block?
If you are about to sell, almost always. Buyers price unmeasured timber defensively, and growers consistently recover the inventory cost several times over in the improved offer.
If it is purely for your own planning, a lighter estimate may be enough. The standard rises sharply when someone else's money depends on the number.
A Number a Buyer Can Verify
Systematic plots, stated methodology, volume by grade and plot coordinates anyone can re-measure. That is what changes an offer.
Over a decade establishing, measuring and managing eucalyptus, pine and indigenous plantations across Uganda. Based in Wakiso, Kampala. Reviewed and updated September 6, 2026.
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