I agree with the fact people interpret such adjectives themselves or won’t use them at all, since it confuses them more than it helps. Difficult to do by just words. You could in theory specify this with a density of “X to Y trees per square meter”, but nobody will use this, really.
The “light forest” is something that clearly has forest character. It’s not a meadow with a few trees, there are still too many to map them individually. That’s the best guide I could come up with, if we want to stay simple.
I’d rather go with examples/images as an aid in addition. Especially in the mountains, this will all be couchmapped by aerial fotos, since a lot of the areas are not even accessible. That’s why I think examples of aerial imagery are somewhat important as well as ground photos.