Interesting - for some reason the term "Scottish" had gone out of my head.
We have had two or three discussions about this recently. Chambers reflects usage, which is not necessarily CORRECT usage. There was a confusing clue in last week's RT (I think) which relied on the Chambers definition of "creek" as "bay".
The Chambers entry on "Scotch" does hint that it is incorrect to apply it to anything other than whisky and mist - though I had forgotten "Scotch eggs". "Scotch Pine" is a good example - it is there in Chambers, but "Scots Pine" is the correct term.