Using high‐resolution imagery to map Scots pine regeneration in the Scottish uplands

1. Native woodland once covered large parts of Scotland but now only occupies about 4% of the land area. The most extensive semi-natural Scots pine (Pinus sylvestris) dominated woodland occurs around the Cairngorm Mountains in Northeast Scotland. Following over a century of minimal tree regeneration due to red-deer grazing, increased deer management has reduced deer numbers over the past few decades in some areas. This has allowed Scots pine trees to regenerate and recolonise areas within and adjacent to the existing forest. The distribution of the regenerating trees is highly variable and the patterns are not fully understood, meaning projections of future forest expansion are uncertain.

2. We used high-resolution imagery to map the location of over 90,000 regenerating Scots pine trees over a 3360 ha study area in the Cairngorms.

3. A field study showed high-resolution imagery detected about half of regenerating pine taller than the ground vegetation, varying from 85% of saplings over 2 m tall to 5% of trees under a meter tall.

4. Distance-to-seed source was the most important factor affecting tree regeneration, with a strong decline in regeneration away from seed source. Regeneration density exceeded 4 pine ha‾¹ at distances up to 375 m from a seed source, with sparse regeneration (1–3 pine ha‾¹) at greater distances.

5. Regeneration was rarer on mire vegetation, with densities 4 times lower than on Calluna heath. Regeneration density declined with elevation and increased with sparser vegetation as indicated by vegetation indices.

6. Practical implications. Our work provides new information on the spatial patterns of natural colonisation of Scots pine trees, improving the ability to predict forest expansion and helping guide woodland restoration efforts.