Did they leave any of it as a remnant or remove it down to the stump and roots?The only reason I ask is that it would have been a wonderful and more than appropriate gesture to have hired a sculptor to carve an ent with a face modelled on the late Tolkien out of what I see in your photograph. Crowd funding it would have been pretty easy and fast given the affection that so many readers have for his works. Even using the stump as the plinth for such a sculpture would be a wonderful reminder of the great writer and his affection for the tree and the place.
@Nicholas - I don't know the answer - but it is a 'serious' Botanical garden, and I rather doubt they would make the stump a sculpture (although that is a pretty good idea!): the tree was not marked with a plaque or anything when I had previously been there, people only knew about it by word of mouth.