Question
my property is 4 ft below my neighbors with a retaining wall holding up his land. on top are 21 blue italian cypress trees, 35 years old and over 25 ft tall, trees are less than 12inches away from the wall. the wall is showing I belive stress cracks and bowed 1/2 inch at base of one tree. do you think the thee roots could be causing a problem to the wall?

Answer
Yes a tree 12 inches from a wall is too close and the roots over time will start to push against the wall. But being that they have been there 35 years and thew wall has not moved but 1/2 inch it sounds like the trees may have adapted their root system away from the wall. I would keep an eye on the wall and look for any cracks that might indicate the wall may break. This will not be a sudden thing so a check once a year comparing last years measurements will give you plenty of time IF the wall looks like it has a problem. It may never get any worst then it is now but is worth watching.