I have a couple sycamore trees that I have kept under 4 feet for years. The bark is beautiful, leaf reduction is possible, and yes, they are hard to kill no matter what you do to them! I had some serious health issues a couple of years back, so I unpotted mine and put them in my flower beds to help insure they stayed healthy when I couldn't give them care. My grandson, bless his heart helped me by making needed hard cuts, and prunes where I told him. I am pretty well recovered now and can use my arm and leg again! But the trees have gone a bit crazy in my "absence. But I thought I would share. These are not, nor will they EVER be bonsai, but they WILL be, once again, my little fantasy trees! As said above, they will tolerate the hard pruning, branch threading and everything else I have to throw at it here soon, and they will be just fine! (Along with getting them in their pots again!)