Designed to thrive in vacuum
or minimal atmosphere conditions, Yggdrasil bushes (or Yggys as they
called
colloquially) may be planted on any suitable body with at least 1/100G
surface
gravity. During its growth phase, the Yggdrasil bush mines minerals,
atmospheric
gases and water out of the soil and stores them within its trunk. If
insufficient volatiles are available on the parent body, they may be
imported
for the use of the bushes. Using a portion of the stored gases, it
ejects a set
of seed packets from itself once every few weeks. Each bush broadcasts
its
position using
bioluminescent
cells on its trunk and leaves. When a sufficient number of bushes have
accumulated their bioluminescent signals naturally form a primitive
local
network. The direction and trajectories of future seed packets are
determined
using data shared by this network in order to maximize plant growth and
area
coverage for the forest as a whole.
When upward growth is complete, each bush begins to extend the growth
of its
canopy of leaves. Canopy growth continues until each bush has
thoroughly
intertwined its canopy with that of its neighbours. At this point the
joined
canopies fuse together into a tough, plastic-like sheath capable of
holding
integrity against standard atmospheric pressure. Completion of the
canopy
across the entire planetary surface triggers a reflex within the
bushes,
causing them to release the atmospheric gases and water stored during
the
growth phase. This release not only creates a livable space under the
canopy
but also frees up the storage spaces inside the trunks for habitation.
As a
result Yggdrasil bushes can provide for much more living volume than a
normal
dyson tree but you have to wait until its final phase of growth to move
in.
In the final phase of their growth, the Yggdrasil bushes alter their
biochemistry to maintain and support the newly created atmosphere.
Symbiotic
soil gardening organisms and other basic elements are budded off of the
bush
root system generating a self-sustaining ecosystem. Starting from a
single seed, a complex of Yggdrasil bushes can convert a smaller world
entirely into a living habitat in as little as twenty years but of
course the larger the world is the longer it will take.
This speed is achievable because the Yggdrasil bush is a variant of the
dyson
tree with a shorter and narrower trunk. However while the
bush
itself only grows to approximately a kilometre in height its need for
at least
1/100G surface gravity means the objects they are planted on already
have a
greater diameter than a full grown dyson tree. This is in no way the
only
variant of the dyson tree and there are various other possibilities
with the
use of this versatile
neogenic
plant. Options include using a variant of the dyson tree (with its
larger
hollow trunk for habitation) to cover a moon or planetoid in a huge
forest and
have its canopy also merging together to hold in an atmosphere. There
are also
variants of the Yggdrasil bushes that can be more easily seeded on
smaller ice
moons and
halo
objects.
They escape the surface gravity restrictions by not ejecting seeds for
new
growth and instead send out surface roots to cover the object.
This is not to say the seed
ejection system is not still in place, only that it is used in a
different way.
Each bush still broadcasts its position using bioluminescent cells on
its trunk
and leaves but in this variant it is the surface roots that receive the
signals. When a surface root grows beyond it's host body's horizon, and
can
thusly no longer receive those signals a response is triggered to grow
a new
trunk. Also, on these lower gravity objects the seed ejection organ
functions
as a seed-launching organ - allowing the bush to colonize new host
objects.
One popular variant of the
smaller object bush is the Fucus vesiculosus - Bladderwrack - a
modification that can develop in Gas Giant rings, with a small
(100-200 meter)
bladder full of breathable air, sometimes with edible fruit and nuts
growing on
the inside. The bladders are loosely connected, with insulated flexible
corridors
between the bladders, and all the ice and rock of the rings
incorporated into
the spaceweed to avoid collision damage. The merging of the surface
roots
instead of the canopy forms the bladder and whenever another ring
object
brushes against one of the bush's branches it captures it by developing
a new
root system at the point of contact. Living space becomes available as
the
roots mine out these objects. With these versatile neogenic plants
there is no
real need for terraforming large worlds. Not when you can easily bush
up the
icy asteroids - assuming you can gene out the low gravity space
sickness
effects reliably.
Dyson trees and Yggdrasil
bushes are not the only ways to roof over a planetoid and others have
come up
with close parallels. The
Softbots
developed the faster growing
Canopy
Plant
for
terraforming
larger worlds, the radiation resistant
Space
Canopy
for roofing over smaller airless worlds and the
Greenbubble,
which is very close to the Bladderwrack in function.
Aleph
Michio Ee adapted the Bluesky
worldhouse to
be photosynthetic, making the Greensky worldhouse. These involve an
adaptation of the Yggdrasil bush with taller, more widely spaced
trunks. This generally allows enough open space to fly a light aircraft
beneath the canopy without hitting the tree
trunks. This is made possible by using air pressure to support the
completed
roof and temporary support pillars (often designed to look like giant
trees
themselves) during the growth stage.
