The ORBX textures might be fine for many places in the world but not so much for the northern parts of my country. I installed it briefly but found trees all over the north beyond the tree line. Places like Iqaluit on Baffin Island had trees and of course this is not reality. So I removed the textures.
Are there trees there only under Orbx and not other textures packs? I'm trying to work out what's amiss. Just replacing textures should just change the appearance of various objects that would appear there no matter what textures they were wearing. If trees appear there only under Orbx, that suggests to me that the autogen itself is being changed or overridden. Either that, or the autogen trees in Orbx are mis-assigned to an autogen value that should produce tundra or icefields or something similar.
If the trees are only there under the Orbx changes, it certainly sounds like the last of the ideas above, namely, the Orbx replacement of default autogen is wrong for tundra (or whatever landclasses Baffin Island has).
That's my uneducated suggestion, at least!