I also noticed that the sims autogenerated trees have greatly increased lately covering the nice new photogrammetry of my home town, Liverpool making it look like a jungle.
I ended up drawing a simple polygon exclusion zone over the photogrammetry area to disable the autogen trees. Works like a charm! Quick and quite simple to do in the scenery editor.
Still would be nice for Asobo to include an option to disable trees but this is another way to remove them locally and in areas where there is only photogrammetry.