How often are you watering the tree?

Water would be the issue, for the Laurels especially. Birch are very well known for their thirsty roots, and the number of years you are talking about have given the tree more than enough time to develop a root system that is capable of draining any water that that area is given through natural or hand watering. Birch are also well known for their shedding of old branches, particularly thin lower branches. They should be pruned out (for the looks of the tree in this instance, more than others) as it is the natural habit of the tree.
If you plan to replant under the tree your best bet would be to attempt to plant in the holes that the dead laurels create because digging new ones could be next to impossible. Additional (and frequent) watering will be necessary to keep new plantings alive under an established birch, long-term.