Stand inventory and structure (BDq / reverse-J)

Measure trees on permanent plots and see the stand’s diameter structure against a target reverse-J, its basal area, growth, dynamics, spatial structure and volume — with a marking quota per size band.

For

Consultant foresters and field crew

Time

10 minutes to read

Where

Field app — Stand data; web — Results › Stand data

Updated

2026-10-03

When to use it

BDq / reverse-J is the stand-data method of UK and Irish CCF practice provisional: it is recommended in Great Britain and Ireland, and in the rest of Europe wherever no national tradition is built in — the structure and quota are standard; volume and carbon are provisional where they rest on form factors (below). Where a country has its own tradition, that is recommended instead and BDq stays available beside it: AFI in France, Belgium and Luxembourg, target diameter in Germany and Austria, and the control method in Switzerland.

Kit

• Diameter tape or calipers (a girth tape is fine — switch the entry to girth), a hypsometer (Vertex) for 10–12 heights, a relascope or prism for angle-count points.
• Tags and paint for permanent plots; a metal detector if centres are buried.
• The phone with the stand saved for offline use.

Plots

Lay out plots with the generator (Plan a field visit): n from your precision target, on a systematic grid or a spatially balanced sample, as concentric 500 m² or 300 m² plots or angle-count points. Big BAF points (a small count BAF and a large measure BAF) are supported.

Record in the field

1. Find the plot and fill Plot visit: centre marker found (so an empty plot still counts), the Big BAF count on Big BAF points, shrub and vegetation notes, the fixed-point photo.
2. Measure every tree ≥ 7.5 cm DBH inside the radius (or every “in” tree at an angle-count point). DBH at 1.3 m on the uphill side; girth is converted (÷ π).
3. Measure heights on 10–12 trees across the size range — they feed volume, carbon and H:D. Include the dominant trees.
4. Tag trees on permanent plots so growth is followed tree by tree. Optional: crown class, role (frame tree…), position (bearing and distance from the centre) for spatial structure, and stem quality A–D on the bottom 3 m.
5. Check the live result before leaving the plot.

Read the result

123

1. Pick the topic — the dot is its status.
2. The chart shows each visit against the target (the band is the tolerance); interventions are marked.
3. The selected visit in words, with the method and version used.

Bars well above the target curve (orange) are where the marking quota falls; classes below it are where recruitment is needed. The headline gives basal area against target and the structural deviation — Σ|actual − target| per class as a share of target basal area.

• Basal-area increment (gross, periodic) and cut ÷ increment — how much was removed against what grew (100 % = cutting the increment).
• Recruitment, mortality, harvest, passage to the next class and survivor growth — from tagged trees measured at two visits.

Spatial structure needs tree positions on fixed-area plots: species mingling (0 = pure groups, 1 = every neighbour differs), DBH differentiation and the uniform angle (regular, random or clumped), from the 4 nearest neighbours with an edge correction. The app says when there are too few positioned trees.

The projection is empirical and conditional — it carries forward how this stand’s own trees grew, died and were cut, with a 90 % interval. It is not a growth model and not a forecast of what you will do.

Volume and carbon

Each tree’s volume comes from the best source recorded, in this order: its own measured volume (a sample tree) → this stand’s VBAR for the species (volume ÷ basal area, from at least 5 sample trees) → your volume table for the species (in the objective) → a provisional form factor × height. The basis is named per species, and form-factor volume stays labelled provisional. On Big BAF points volume = mean VBAR × count basal area, with its combined error. Carbon follows volume and is a basis for reporting, not a claimed carbon-code calculation.

Ireland and the UK: the Irish and British tariff tables are not shipped yet — measure VBAR sample trees, or enter the tariff volumes you use as the species’ volume table in the objective. The UK Woodland Carbon Code’s own calculations are not reproduced.

France: set a Schaeffer tariff per species in the objective, after your volume table in the order above: R (rapide) for mixed or large-crowned stands, L (lent) for homogeneous even-aged stands, then the number (e.g. R12; * for every other species). Tariffs start at 15 cm. Or choose EMERGE total aerial volume (stem and branches, Deleuze et al. 2014); it needs sample heights, and carbon then uses no expansion factor. Both are designed for France: elsewhere the app adds a caution, so check them against a few measured trees. EMERGE stem and crown volumes are not available yet.

Outside Ireland and the UK: enter your national volume tariff or yield table per species as the volume table in the objective (or measure VBAR sample trees); no national tables are shipped.

Quality checks

• Record empty plots; tick the centre marker so the plot counts.
• Do not mix diameter and girth: use the switch, never enter a girth as a diameter.
• Heights on the dominant trees, or H:D and volume are biased.
• Keep plot references and tags the same at every visit — dynamics need re-measured trees.
• Assisted values (voice, camera, instrument) count only after you accept them; the evaluation says how many were left out.

Sources: de Liocourt (1898); Forest Research BDq calculator; Pro Silva Ireland practice; spatial indices after Gadow and Pommerening; Big BAF after Marshall, Iles & Bell (2004) and Lynch et al. (2021); ratio estimator, Cochran (1977).