Question
our tree is old and mature and very large and is in need of the lower ring of branches to be cut. The branches are heavy and laying on our arborvitae. Can we trim the branches off OR back without killing the spruce???

Answer
Pruning the branches will not harm the tree. Prune them back to the trunk about 1/4 inch from the trunk not flush. This will allow the wound to heal over better. On large trees it is best to make the first cut about a foot from the trunk on the under side then cut the branch off from the top leaving a stub about a foot long. Then you can prune off the stub and the heavy limb will not split the bark on the trunk.
Here is a web link to how to prune trees with a drawing of the large limb pruning method.
http://www.ces.ncsu.edu/depts/hort/consumer/factsheets/trees-new/text/pruning.ht...
Now is the best time to prune these trees.