We want to plant some trees in our yard, but have some phone and electrical wires running along the back of our yard. How far in front or behind the wires can we plant either a River Birch or a Bald Cypress?

You should first contact the City and have the lines marked if they are underground. Usually high voltage lines are several feet in the ground and lines like cable, telephone can be anywhere from a few inches to 18 inches. Service electric to your home will be 3-4 feet or so. Even if the lines are marked, you should dig with great caution. If above ground, your choice of plants should be ones that will not interfere with the lines as the trees mature or understand that the company charged with keeping the lines clear have the right to prune accordingly. there are cultivars of River Birch that have differing mature heights and widths. While there are cultivars of Bald Cypress, I do not know of any really small statured types. Shawnee Brave is more narrow and upright, but at maturity is still 30+ feet across.

Sorry, Let me clarify the question: how far AWAY from a line of wires is it safe to plant a larger tree. Is there a guideline? "Julie" has been to our house and we have nothing underground and I want to make sure I am planting trees far enough AWAY from the wires that they won't interfere or need to be trimmed

The Potential spread listed in references is based on a mature plant taking let's say 20-25 years to attain this size. Taking that 40 feet diameter suggests 20 feet away. This may not be possible or realistic for your yard or design. 12-15 feet may be a good compromise. When branches do reach the wires and will be trimmed, they would be trimming back the ends typically and not into major branches closer to the trunk. Proper heading back cuts will minimize the visual damage to the tree.