Windblow — stability (H:D) and the post-storm windblow record
Read the stand’s slenderness (H:D) against exposure-adjusted thresholds before a storm, and map windblown areas and the standing edge after one — evidence for a felling licence or insurance conversation.
- For
- Consultant foresters
- Time
- 6 minutes to read
- Where
- Web — Results › Windblow & stability, and Plan & evidence › Windblow; field app — Windblow
- Updated
On this page
Before a storm: H:D stability
H:D is tree height divided by stem diameter (both in the same unit). Slender trees (high H:D) are less wind-firm, especially after thinning. The app computes it from the stand-data tally — the dominant stems’ measured heights — against thresholds of about 80 (caution) and 100 (high), adjusted for the stand’s exposure. provisional: the thresholds are defaults. Flags only — the call is yours.
- Set the stand’s exposure on the stand form (Set up a stand); it shifts both thresholds.
- Make sure the dominant trees are among the stand-data sample heights.
- Windthrown stems can also be recorded on the phone as an observation:
After a storm: record the windblow
Stand › Plan & evidence › Windblow keeps each windblown area or point with the forester’s view of the standing edge — the evidence a felling licence, a grant authority or an insurer asks for.
Republic of Ireland: DAFM’s 2025 guidance asks for windblow mapped as separate plots, the share of the area blown and a forester’s assessment of the stability of the standing trees.
- 1 Area, share, stems and H:D
- 2 Record windblow
- 3 Each area or point, with the standing edge
- The tiles — area blown, share of the stand, areas · points · stems, and the stand’s H:D result.
- Choose Record windblow.
- The list — each area or point, its size, and the standing edge.
- 1 Draw the area (or place a point)
- 2 Date, extent and stems
- 3 Your view of the standing edge
- 4 Record windblow
- Draw the area on the map (Draw polygon, click the corners, Finish polygon), or Place point for a single tree or small group.
- Date observed, extent, stems thrown.
- The standing edge — stable, some unstable trees, unstable — and what you saw (root-plate lift, lean, cracked stems, slender edge trees).
- Choose Record windblow. The area is computed on the server.
Overlapping areas or areas crossing the stand boundary are warned about.
The windblow record feeds the WIS CCF checklist (Grant evidence).
- Walking the edge of a windblown area with GPS on the phone is not on the field app’s screens yet (the app’s rules for it — fixes worse than 15 m dropped, the ring closed — are built and show as walked when used); draw areas on the web.
- It does not file a felling licence, notify the forest authority (DAFM, the Forestry Commission, Scottish Forestry…) or make an insurance claim — it supplies the evidence.
- No wind-risk model (e.g. ForestGALES): H:D thresholds only.
Sources: H:D guidance for conifer stability (Forest Research: ~80 caution, ~100 high); DAFM FAQ: Forestry windblow and storm damage 2025, v2.