I'm never quite sure why people think of sycamore as a weed tree. Yes they seed all over the place but either animals graze them away or if they appear in the garden and you don't want them then pull them out, otherwise they will grow into a beautiful, large, well shaped and shady tree. I'm not a tree snob - I love them. We also grow Field maple which is related to sycamore and forms a very nice small tree with a magical bark, or fills out the hedgerow beautifully. Our sheep certainly graze the field maples right back to the trunks and relish them