The subalpine fir or Abies lasiocarpa is an evergreen found slightly below the timberline in the mountainous forest regions of North America (west and southwest). It is normally not found as a specimen or ornamental tree in landscape design. If it is used it should be used in the north or at high elevations. Evergreen trees require pruning to remove diseased or damaged branches, to maintain a certain size (width) within your landscape design, and to provide clearance underneath the tree.
Remove any damaged or diseased branch or branches immediately. Make a clean cut, and do not leave a stub. Clean cuts insure that the wound heals properly. Do this as soon as you notice the damage; the tree does not have to be in its dormant state.
Use your hand shears to maintain the width of the tree (head back new growth); make your cut just in front of a lateral bud. Not only will this maintain the width of the tree, but it will also produce a denser tree. Pruning of this nature should be performed in early spring.
Decide if you want to remove any lower branches. Removing lower branches does provide clearance underneath the tree, but it also changes its appearance. It comes down to personal preference. One of the pluses of removing lower branches is that it allows for easier clean up underneath the tree, and you can also plant ground cover or grass under the tree. Do this in early spring or late fall/early winter.