# Mapping millions of little trees across the Cairngorms with airborne LiDAR
*2026-09-24 — note*
It's been a [rough year for wildfires](https://en.wikipedia.org/wiki/2026_Cairngorms_wildfire) in the Scottish Highlands, so I'm delighted to have some good news in our [new paper](https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/1365-2664.70561) out today\!
Using airborne LiDAR, we've found that the native forests across the [Cairngorms Connect](https://cairngormsconnect.org.uk/) restoration area are steadily expanding, with millions of new young trees taking root in open ground that has been treeless for centuries.
[Tracking and modelling native woodland expansion in the Scottish Highlands using LiDAR](https://anil.recoil.org/papers/2026-cairngorms-expansion), led by Sudina Thapa and [Aland Chan](https://eo.conservation.cam.ac.uk/people/aland-chan/) in [David Coomes](https://coomeslab.org)'s group at the [Centre for Landscape Regeneration](https://www.clr.conservation.cam.ac.uk/),
is open-access, and the University has published [an explainer](https://www.cam.ac.uk/research/news/successful-woodland-expansion-in-scotlands-cairngorms-revealed-in-aerial-maps) as well.
## Oh Deer, oh deer, oh deer
Only about 4% of Scotland's [original native forest](https://en.wikipedia.org/wiki/Caledonian_Forest) is still intact, with the rest
long since cleared (usually for agriculture) and replaced by heath, bog and
grassland. [Cairngorms Connect](https://cairngormsconnect.org.uk/) is the largest contiguous nature restoration
partnership in the UK, across 60k hectares of the [Cairngorms National Park](https://en.wikipedia.org/wiki/Cairngorms_National_Park). Their
goal is to _double_ the forest extent, ideally through natural regeneration.
So what stops the forest from naturally growing into surrounding land? Deer\!
Our [adorable](https://en.wikipedia.org/wiki/Bambi) ungulate friends chew
saplings and kill them before they become mature trees. Since fences are
impractical over this large an area, the partnership has instead reduced deer
through sustained culling so seedlings which would previously have been gobbled
could instead grow into mature trees.
## Commissioning a LiDAR flight
What our paper does is to help evaluate the efficacy of the intervention. Field
surveys of saplings are obviously labour intensive if we want to cover rough
Highland terrain.
So back in 2023, we got in touch with [Fugro Geospatial](https://www.fugro.com/) to commission an airborne survey
over a big chunk of the Cairngorms Connect area. A light aircraft flew ~600m above the ground with a
[Riegl](https://www.riegl.com/) waveform laser scanner, and collected a LiDAR
point cloud for us along with 10cm resolution RGB and near-infrared aerial imagery. This dataset has
since fed into a number of projects at the CLR, from shrub ecology and carbon to
deadwood detection.
A LiDAR point cloud of individual trees in the Cairngorms, coloured by height (credit: Aland Chan)
Once the survey came through, data processing was quite a bit of computation.
The full set of imagery was around 6TB raw. The LiDAR itself was excellent, but the first
orthomosaics we received were off by 2-5m in their coordinates, which was enough
to misalign roads (and obviously trees).
While conventional photogrammetry tools can fix this via "[tie points](https://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/OWENS/LECT5/node5.html)"
across overlapping photos, this is difficult to do with trees at different angles.
We therefore went back to the original images and reconstructed the mosaics ourselves.
The analysis pipeline is subtle because saplings are about the same height as
heather and bracken. Conventional classification algorithms tend to lump small objects into the ground, so Aland built a
[processing pipeline](https://github.com/alandhyc/lidarSHM) that preserves smaller
features in the canopy height model. This was actually _too_ sensitive as it also detected
lots of bracken, so Sudina subtracted the local average height to remove it before singling out treetops and [delineated tree crowns](https://github.com/alandhyc/minitree).
We validated this against trees that were manually geolocated+measured.
Clusters of regenerating trees started to become detectable as soon as they
outgrew surrounding shrubs, with 83% detected at 1.4-1.6m and over 95% above 1.8m.
This is happily right around the 'deer chewing' line, so our method can find
the trees that have "escaped" and will likely grow into mature woodland.
## Seeing the trees for the woods
We found \>6 million individual trees in the region, of
which 2.65 million were young trees under five metres tall. The good news is that a large swathe of
previously open land now features young saplings with a good density, largely
established naturally.
> "The ability to map regenerating trees so precisely, at such a huge scale, is
> a breakthrough for monitoring nature restoration at a landscape scale. It means
> we can effectively map young trees, assess whether restoration targets are
> being met, and inform future restoration work."
> \-- [Aland Chan](https://www.cam.ac.uk/research/news/successful-woodland-expansion-in-scotlands-cairngorms-revealed-in-aerial-maps), 2026
We then fitted a model to identify the drivers of successful regeneration. Most
young trees cluster near edges of existing forest, although some plucky
pioneers are growing further away. Elevation, habitat type and deer density
also all strongly affect establishment; fewer young trees take hold in
boggy areas. Overall though, total woodland has definitely increased in areas
where deer control took place, yay\!
## What next after the fires
The Scottish Government is now funding a fresh national airborne LiDAR survey,
which is obviously excellent news as we could only rustle up funds back in 2023
for a small swathe (thanks to Tarides for that!).
On the computing side, David and I are learning from [Michael Dales](https://mynameismwd.org) [recent work](https://digitalflapjack.com/weeknotes/seeing-the-trees-from-the-forest/)
on visualising lidar to combine it with [Tessera](https://anil.recoil.org/projects/tessera).
LiDAR flights are expensive even with the government involved, so the more we can
leverage much more easily accessible satellite data, the better our tree counts will be.
Well done to Sudina, Aland and David for seeing this through over the past
three years, and many thanks to all the partners in Cairngorms Connect and the
field teams who spent many hours manually measuring saplings deep in the heather\!
Synopsis: A good news paper in the Journal of Applied Ecology, using airborne LiDAR over Cairngorms Connect to map 2.65 million young trees and finding deer management is working.
Words: 859
## Related
- [Tracking and modelling native woodland expansion in the Scottish Highlands using LiDAR](https://anil.recoil.org/papers/2026-cairngorms-expansion) (paper, 2026-09-01)
- [TESSERA, a pixelwise geospatial foundation model](https://anil.recoil.org/projects/tessera) (project, 2025-01-01)
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Canonical: https://anil.recoil.org/notes/cairngorms-woodland-expansion
Type: note
License: CC BY 4.0
Tags: conservation, nature, biodiversity, climate, landuse, scotland, spatial
