C‑DRONE
Tiled rooftops seen from above during a drone inspection

C-DRONE GUIDE · 2 AUGUST 2026

Mapping windthrow after a storm by drone: quantifying the damage, prioritising salvage logging, price

A winter storm crosses a forest in a matter of hours and leaves behind tens, sometimes hundreds of hectares of broken or uprooted trees — windthrow, known in French forestry as "chablis". Its volume shapes everything that follows: organising salvage before the wood loses value, reopening access tracks, and above all stopping bark beetles from settling into freshly downed logs before spreading to standing stands nearby. A traditional survey, on foot and stand by stand, takes weeks across a forest of several thousand hectares, often inaccessible until the tracks reopen. The drone changes the scale of the diagnosis: a flight of a few hours is enough to map the extent of the windthrow and estimate its volume, without waiting for the ground to become passable again. Here is the method, its limits compared with a reference cubing, and the prices charged in 2026.

Published on 2 August 2026, reviewed on 6 August 2026 — regulations in force as of August 2026.

Windthrow: a race against time after the storm

A fallen tree is not a tree that waits: within the first few weeks, the wood starts losing value — blue-stain fungus in conifers, decay fungi, drying cracks — and its commercial worth erodes as time passes, even before it is hauled out. The major storms that have marked French forestry, from Lothar and Martin in December 1999 to Klaus in 2009 in the Landes de Gascogne, each felled several tens of millions of cubic metres of timber within hours — a surge so sudden it saturated the timber industry for years afterwards and forced the setup of sprinkler-irrigated storage yards to slow the wood's decay.

The second issue is health-related: freshly felled conifer logs make an ideal breeding ground for bark beetles (notably the spruce typographer), which multiply there en masse before spreading to still-standing stands at the edge of the windthrow — a risk covered in detail in our guide to bark-beetle detection by multispectral drone. The longer salvage of the downed timber is delayed, the more this secondary risk grows: knowing the extent and volume of the windthrow quickly directly shapes how fast the forest manager, the ONF or the insurer can react.

Mapping fallen trees by drone: video, photogrammetry, LiDAR

The first approach remains classic photogrammetry: an RGB flight on a parallel-strip pattern produces an orthomosaic and a canopy height model, and comparing it with a pre-storm survey brings out the gaps and the fallen crowns. The difficulty specific to windthrow is that broken crowns overlap and hide part of the trunks from directly above — an obstacle a 2022 study published in Remote Sensing by Furukawa, Morimoto, Yoshimura, Koi, Shibata and Kaneko tried to work around by comparing the static orthomosaic with a video-based approach (full motion video): filmed continuously from the drone, the video conveys movement and depth context that helps tell broken trees apart from uprooted ones, where the still image sometimes confuses the two (see the study on Google Scholar).

To get to a volume figure, onboard LiDAR takes over: a 2025 study published in the journal Drones by Badal, Cristan and Narine, of Auburn University, compared several classifiers (random forest, maximum likelihood, decision tree) for mapping catastrophic-windstorm damage on a working forest, using a LiDAR canopy height model combined with RGB imagery: the LiDAR + RGB combination processed with a random forest classifier delivered the best classification accuracy (see the study on Google Scholar). The principle matches the one detailed in our guide to forest carbon inventory by LiDAR: the same canopy-height data, used here to tell standing wood apart from downed wood rather than to estimate biomass.

Organising the salvage: regulations, prioritisation, the bark-beetle link

A storm-hit forest remains, from a regulatory standpoint, rural terrain far from any person: the flight takes place under open-category subcategory A3, subject to first checking on the Géoportail map that the area is not under a temporary restriction linked to the emergency response or a helicopter corridor mobilised for the crisis — our guide to the open versus specific drone category covers these thresholds. Residual wind after a storm passes is often still strong: the provider checks the weather window before taking off, a call detailed in our guide to drones and weather, when to cancel a flight.

On the ground, aerial mapping above all avoids exposing a forestry worker to a genuine hazard: surveying dense windthrow on foot, bristling with hung-up broken stems (snapped trunks caught by neighbouring trees) and uprooted stumps, ranks among the most accident-prone situations in the trade. The drone ranks, from a distance, which sectors are most affected and warrant a rapid response from loggers, and which ground remains safe enough for a follow-up on-foot survey — a prioritisation that follows the same logic as our guide to forestry management by drone, applied here to an emergency rather than routine monitoring. Once the timber is hauled to the roadside or the sawmill yard, the pile is cubed using the method detailed in our guide to log pile volume by drone.

Limits compared with a reference cubing, and 2026 prices

Drone mapping gives a reliable estimate of the extent and an order-of-magnitude volume, not a contractual tree-by-tree cubing: the interlocking crowns of dense windthrow make it hard to tell two neighbouring trunks apart, and trees left standing but weakened (leaning, roots loosened without being fully down) often escape automatic detection, which more easily picks out a trunk clearly on the ground. A targeted ground check on the sectors flagged as priorities is therefore still recommended before committing to a final marking-for-felling round or an insurance claim. The aerial data serves as a prioritisation map, not an expert report enforceable as such.

Orders of magnitude observed in France in 2026 (excl. VAT):

Our guide to how much a drone service costs details the parameters that make these amounts vary. This service falls under our drone surveying and photogrammetry offering; request a quote stating the affected area, the dominant species and the time elapsed since the storm.

Frequently asked questions

Does the drone replace the forester or the ground-based marking-for-felling round?

No. The drone quickly maps the extent of the windthrow and estimates its volume, which helps prioritise the sectors needing urgent attention. The salvage decision, tree-by-tree marking and contractual cubing remain the responsibility of the forest manager and the on-the-ground expert.

How soon after the storm should the drone fly?

As soon as possible once the weather has stabilised, ideally within days: the map guides the organisation of salvage logging before the wood loses value and before the risk of bark-beetle proliferation rises on freshly felled conifers.

Does residual wind after the storm rule out flying?

It can delay it by a few days: a serious remote pilot checks the weather window (wind, gusts) before taking off rather than forcing a flight in degraded conditions. A windthrown forest remains accessible to drones as soon as wind drops back below the usual operational thresholds.

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Put it into practice

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