Case study: LiDAR inventory of a Christmas tree plantation

The mandate

Site

a Christmas tree plantation in Quebec’s Eastern Townships, about 41 hectares, with blocks of mixed ages — from young seedlings to trees ready to cut.

Objective

count every tree, measure its height and produce a clear portrait of the plantation by height class.

Constraint

the blocks are bordered by woodlots, hedges and scrub that must be distinguished automatically from planted firs.

Our approach

1. 1

   Aerial survey

   We flew 6 automated missions with a DJI Zenmuse L1 LiDAR sensor. LiDAR measures terrain with laser pulses. It captures both ground and vegetation, and the built-in camera colourizes each point. In total, more than 1.2 billion points were collected.

2. 2

   Fusion and quality control

   The 6 point clouds were merged and aligned. We checked vertical agreement on reference surfaces such as roads, to within a few centimetres.

3. 3

   Terrain and height model

   True ground is extracted under the vegetation. Each tree’s height is then measured above the ground — not above an approximate relief.

4. 4

   Automatic detection

   Each fir is located as a local peak in the height model. A regularity filter keeps only trees aligned in plantation rows. Scrub, shrubs and spontaneous vegetation are rejected automatically, without drawing zones by hand.

5. 5

   Indicators

   For each tree we compute position, height and, for established specimens, crown width. Crown colour is also compared with surrounding grass, to flag trees that deserve a field visit (pale top: yellowing, dead tree or weed pressure).

Results

Breakdown by height

• under 0.5 m26,474 trees
• 0.5 to 1 m4,442
• 1 to 1.5 m2,766
• 1.5 to 2 m2,278
• over 2 m2,999

At a glance, the grower sees that the plantation is mostly young. They know how many trees will reach sale size in the coming seasons — and where they are.

What the grower receives

• An inventory by block: tree counts by height class, to plan harvest and sales.
• A GIS file with one point per tree: usable in QGIS, Google Earth or on a phone in the field.
• Terrain and height models at 20 cm: useful for spotting wet areas, drainage issues and uneven growth.
• A list of trees to check first.
• An interactive map to view and share easily.

What’s next? Year-over-year monitoring

The real value comes with a second survey. Comparing two seasons measures each tree’s actual growth, flags areas that plateau and tracks replants. The inventory then becomes a management tool.