Good morning everyone.
First post from a newbie here but I have been flight simming since 1982 (ZX Spectrum of course!)
I have exactly the same issues as the OP and a couple of other Brits here - our upland moors and mountains have sprouted random trees.
Having read your thoughts, I went with the buyable DLC that is BIJAN's FOUR SEASON pack; I went for flights over my own area in the west Pennines, then Kinder, around the Lake District. It seems to have done a lot for the landscape and scenery, the colours are spot on for yellowed and brown grasses, and best of all - barely any trees on the fells above a certain height/altitude so I am so far happy to say the application does what it says on the tin. I'll have a play with it - I have read there is an option for British Gorse bushes somewhere - but the only negative I seem to have found so far is that on Kinder, the rock outcrops have all been re-imagined as little houses.... oh well!