Yea, totally random - on 1st playthrough abandoned at iron age, my starter island had gigantic black forest in middle and swamp in lower south. So meadows all around outskirts, giant BF middle, tip of southern area swamp. Nice all around starter island.

But on my new 2nd run just started, my starter island only has meadows and one small BF in the south, nothing else. The BF is quite small, enough so I had to replant some trees for easy access to core wood.

Still searching for swamp with my boat but keep finding islands with only meadows+BF.