Aside from being aesthetically pleasing and unique, using actual tree rounds as speaker enclosures is beneficial to the overall speaker design because it results in an almost seam-free cabinet, thick and acoustically dead enclosure material, and non-parallel internal sides which help to reduce unwanted frequency amplification and reverberation.
This Instructable describes the unique process of how I built these specific tree speakers, and is not meant to be a complete and comprehensive guide to speaker building. For that, please see my Instructable on How to Build Custom Speakers, which the DIY speaker builder working on his or her own project will find much more helpful.
I think that the appropriate question to ask here is not "why build speakers out of a tree", but rather, "why not"?
Step 1: Story
The giant tree's death was unfortunate and sad, but the loss of the tree ultimately led to the birth of something else: The Elm Tree Project. The joint venture between Brown University and The Rhode Island School of Design produced a set of classes, exhibitions and specially designed studios, all built specifically to explore and produce various forms of art that could be made from the deceased tree.
I was lucky enough to be a part of this unique program during my time at school, and have finally gotten around to documenting some of the work that I produced during my involvement with The Elm Tree Project on Instructables.