Question
I have a 30 foot fir tree that I have recently put some dirt around the base in an effort to re-landscape.  I was then told by someone else after the fact that this will kill the tree in a couple of years as the tree cannot breathe.  The dirt was made in a mound no more than a foot around the existing base of the tree.  Does this in fact Kill the tree over time and what is the tolerance of a fir at the base?

Answer
Yes soil added around a tree trunk can damage the tree by compressing the soil and the air pockets are destroyed. It will first show up as branch dieback and it could over time kill the tree. I would remove the soil from the tree down to where the trunk starts to flare out.