During the terrain overhaul for 25 they got removed. Maybe @wowgetoffyourcellphone knows why?
But as some players miss them, they are added back in. This also differentiates the biomes more.
See:
https://code.wildfiregames.com/D4086#181278
and
https://wildfiregames.com/forum/topic/51306-thread-for-posting-suggestions-for-alpha-26/?do=findComment&comment=446682