Three things we know about Haida Gwaii:
1. About 14,500 calendar years ago it was a temperate tundra environment, with no trees. The first trees, pine, appear about 14,000 years ago and there is progressive forest infilling thereafter, with the modern species mixture in place by about 3,000 years ago.
2. It has an impoverished suite of large land mammals – historically, these were limited to black bear, caribou, marten, ermine, a vole and a shrew. We know that 13,000 years ago there were also deer and brown bear on the islands, and quite likely other species as well.
3. It used to be much larger than in the present. With lower sea levels at the end of the last ice age, Hecate Strait was largely dry land, exposing a large, unglaciated, coastal plain that became rapidly flooded.
It seems to me that we can add a fourth thing we know: