Think of Leylandii and thoughts of suburban hedges and disputes over encroachment come to mind. I first came across this hybrid 25 years ago in Ireland in tree form and was amazed by their presence. A Nootka cross Monterey Cypress originated locally when in 1888 at Leighton Hall near Welshpool, a gardener created this wonder that can grow very fast up to heights of 130 feet. As it is sterile a Leylandii produces no food for wildlife however it is shelter for bats and birds in its dense foliage, and as a hibernation site for many insects it is a useful addition to any biosphere. Like all conifers it tends to acidify the soil so reducing the presence of earthworms but the roots stabilize the soil.
By coincidence the builder/architect who in 1704 remodelled Treflach Hall was one Robert Thomas Leighton of The Leighton Park Estate. So these trees are quite at home here and part of the local history.