dying trees
By Nickifoster
United Kingdom 
we have planted six leylandi trees in the surrounding area of a dead sycamore. The sycamore is still standing, though severely cut back. Over a period of three years the leylandi have died one by one - we have three left. Is this due to soil cionditions caused by the dead tree?
6 Oct, 2008
Answers
Do you know what the sycamore died from? Any chance it could be honey fungus?
http://www.rhs.org.uk/advice/profiles1100/honey_fungus.asp
6 Oct, 2008
sorry im not that well informed but sycamores are normaly hard as nails and conifers.if there bothe dying there mite be a deeper more worrying problem with the land.poisan or something sorry to worry you
6 Oct, 2008
I agree with Nosey potter. Chances are the sycamore is still living and fighting back.
6 Oct, 2008
i dont know for sure but most conifers have shallow roots as they are real forest trees.the sycamore if its only cut back is probably alive including its long reaching roots.as you know leylandi are or can be a problem.id say your spot on with what you say. id make sure the sycamore is dead then dress the topsoil with some manure and start again
6 Oct, 2008