What kind of climate is there in Yliakum?
Since it has been said that is is too small for ordinary rain to gather it must be quite weird.
It may be also possible that some water leaks from the surface and appears as rain in Yliakum but that does not sound very safe, especially for thick rain.
On the other hand, the temperate climate similar to that in Europe or that in the middle of North America is heavily dependent on rain. Should you get no rain, grass would grow only a few meters distance from water and trees perhaps a few more meters further.
coldYliakum could be relatively dark, cold, and wet place if the Crystal was not too bright. We might not notice as the characters would be adapted for that.
Since the Crystal radiates more infrared than light it is more likely to be so.
In this case, we would probably get many ferns and fungi, possibly huge, and some plants with large dark leaves.
This would also get rid of the weird looking trees as they can be turned into decent ferns or replaced by mushrooms.
There would be no rain, but not much vaporization either. Everything would be wet and qiute cold all the time.
Though it is certainly possible, it probably would not be the world of choice for Enkidukai and other races that like warm and dry places to live in.
hotAnother possibility would be to make the highest level very warm with tropical climate.
There would be enough vaporization from the ground and the water that comes through the walls that clouds would shape even in the limited space. And rain once or twice a day depending on the time of the year.
Again, a banana tree or a cocoa tree sounds easier to model than an oak (and is very near to what we already got

)
The colder lower levels could be something like temperate climate with the reain falling there as well.
There is even a nice way for regularing the level of the sea (if it is not going to be done in a magical way). As the water flows in and raises to the sixth level it will pour into large and shallow swamps that warm up and evaporate quickly.
Either way, the climate would be very wet. Anything organic would rot quite quickly and iron would get eaten by rust.