Although biter bases will appear when previewing a map, dense trees seems to suppress the placement of biter bases when a map is actually started/in play. Screenshots for illustration:
Preview:
Map in play:
[0.17.2] preview biter bases do not match map in play
Re: [0.17.2] preview biter bases do not match map in play
Thanks for the report: the preview is not perfect - by design - it's just an approximation of what the game thinks will be generated.
If you want to get ahold of me I'm almost always on Discord.
Re: [0.17.2] preview biter bases do not match map in play
Nonetheless, I don't think most players would expect that high tree coverage settings would suppress biter spawns. Would it be possible to have biter spawns take priority over tree spawns, or at least have the preview respect spawn priorities?