Imagine you are lost in a desert, it is insanely hot and dry and you can feel yourself dying with every step you take.
You crest a dune, and there lies a cupula ... or what appears to be a cupula.
You drag yourself closer with your last vestiges of strength, try to get inside ... leaves part and you find yourself inside a living cathedral where it is cool and moist ...
This is the Oasis Tree, an alien tree used for terraforming. Large seeds allow extreme roots to grow first, diving down deep, deep into the Earth and finding water beneath the surface.
Once this water has been found, the tree develops rapidly, developing a strong stem and drooping branches which enclose the space around itself and create a miniature habitat with ideal conditions for life to survive and develop from there.
The Oasis Tree is the beginning ...
Oasis Tree, Silvia Hartmann 2015