In one particular part of the young coniferous plantation, Scots Pine trees are growing in a peculiar manner. This is a shot of an affected tree:
Note the 'pom pom' effect on the branches.
Here's a close-up of an affected shoot:
The damage appears to be caused by clusters of needles dying and dropping off:
This shot shows that multiple areas of single plants are simultaneously affected:
I was told that the effect can be caused by the European Pine Sawfly, but my research shows that this sawfly damages needles in a completely different way: by eating them down to the branch. So it looks like I'm back to square one on this one.