I think that might be unknowable. The label ‘Thornthwaite Forest’ appears on the OS OpenData StreetView dataset, but on no other OSM layer. I can’t find any reference to it on the NLS historic maps at https://maps.nls.uk/geo/explore/side-by-side/#zoom=15.4&lat=54.60623&lon=-3.24466&layers=174&right=ESRIWorld.

So the only information I can find about it is a single point label. There’s unlikely to be local knowledge about exactly which bit of the forest it is, as it’s all post-WW2 plantation forest and is far away from settlements, so nobody will have any close attachment to it.

So ttbomk it’s best left as a node.