Now for I go any further I want to make a couple statements. One architecture is not my strong point. Two trees are also not area I feel I do my best work in. Therefore combining buildings and trees into one subject really pushes the limits of my drawing skills, but pushing oneself is the only way you grow.
In the past I have posted several drawings and sketches related to landmarks I have seen in my Equestria dreamscape. link link link link
Since the first place Petina and I stayed at upon arriving in Ponyville was the town library I decided to do a B/W study of it.
I have not gotten a clear story about the origin of the library yet. Even Twilight seems to be uncertain about the facts surrounding it. Some ponies say that the tree was grown specifically to become the library. Others say the tree was already there and simply adapted to the task. Sometime I should ask either Celestia or Granny Smith for their take on it.
One thing that is for certain is that the tree has some very strong earth magic connected to it. Although it is technically a deciduous tree it seems to keep most of its foliage year round. Even during the cold freeze that occur every year in the winter.
Another unusual aspect about the tree is that there is a small spring directly under it that provides water for both the tree and the occupants of the library. Also an ingenious, or insane, pony figured out how to connect it to the town sewer and gas lines some time in the last decade or so.
Finally the tree seems to be bigger on the inside than its outside dimensions allow for. Also it must have some of the deepest roots around since the is a basement under the library and the tree seems to none the worse for it?