 Particularly problematic local trees include the sycamore, lime, sweet and horse chestnut, ash, and poplar, which regrow or coppice after cutting back, and have large, flat leaves, which stick to the line and cause severe slippery rail.Other types of tree that cause problems are quick-growing, pioneering trees, or those producing a substantial amount of leaves.Poplars are particularly troubling because they tend to shed limbs.