When I was a kid, I first saw the fantasy maps in the Lord of the Rings, with its exquisite penmanship, and the stylized, pseudo-medieval icons symbolizing mountains, cities, forests, and so on.
To my mind, however, I had a hard time imagining this landscape. If trees on the map indicated forests, then in my head, the rest of the map would be grasslands completely devoid of tree-cover, which seemed oddly barren for what was to a good extent fantasy-northwestern Europe This seemed utterly bizarre to me. I remember asking my dad about this, and he told me that the trees on the map only referred to particularly dense woodlands, and that indeed there were probably trees all around, just less so.
I've thought about this a bit, as it's by now a tradition for many fantasy maps to dot in some woods here and there and name them, sometimes very deliberately, sometimes more for aesthetic purposes - but the question of "what about outside of the woods?" is something I always carry with me. And thus Glorantha.
This is not necessarily a question solely about to what degree Gloranthan areas that aren't explicitly covered in trees on the maps have some tree cover on the ground as well (although some discussion on that is welcome - I remember reading or watching a video that said the Bronze Age saw the largest agricultural footprint in terms of square miles in the history of Britain, for example), but it's perhaps equally a question of what makes a forest with a big F, and what are just a bunch of trees just hanging about.
Is there simply a density equation going on? Or is it mixed into mythical or political issues, such as the residence of woodland spirits, aldryami, forest-people who call that area their home. For example, maps often do not show woodlands around the Vent - yet woodlands would be necessary for large scale swidden agriculture to work, if I understand it correctly. Is Junora really that barren of dense woodlands? These are all just examples.
As I said, this is as much a topic of cartography and symbolism as it is about Gloranthan geography as-is - though it is both.
EDIT: And of course, this does vary between different kinds of maps, lest I come off as treating not only all fantasy-style maps, but also all Glorantha maps, with too broad strokes.