This is what happened to a rather nice specimen of Cedrus atlantica Glauca, the blue Atlas cedar I had by the front gate. I think the mistake was to try and restrict its growth but there was really no alternative as the tree was already pushing the telephone wires. I used to prune it myself but had left it to a professional arborist who I think just topped it instead of also thinning the growth out at the top causing it to become congested. The general consensus of opinion was that the tree had been pruned too heavily which eventually traumatised it, no evidence of any disease was found.

A sad loss.