(above)  Calf Island wall in Roaring water bay off Skibberean in Ireland.
No ferry visits this island.  I had to kayak there from Schull.

(above) - The Mourne Wall, 23 miles long.

Built around the watershed of a reservoir in Northern Ireland, between the years 1904 and 1922 to protect the water supply to Belfast, Norther Island.  Built of locally quarried granite.

Trees and Walls

Trees and walls don't generally mix.  Trees close to a wall will normally push the wall over as they grow or get rocked by the wind.  To avoid cutting down trees in or near walls which the owner doesn't want removed there are a couple of methods..  

Here's one method, spotted in the Yorkshire Dales.  In this case the waller has run the wall as close as he needed to the tree and left a gap with properly built wall ends.  I've also seen a wall built around a tree.  Either way it needs to be at least two or three feet away from the base of the tree.  Any gap which stock might escape through can simply stopped up by using a small amount of timber.  

If roots are a problem on their own then it is normal to bridge them with stone to avoid the possibility of the root or new roots lifting any foundation stones.

ber or wire fencing.