Question
I have a native tulip popular tree on my property which is approximately 12 inches in diameter and in apparent good health. It is in a grove of established populars and is growing on solid dry ground. It is leaning approximately 10 degrees toward an adjoining house whose owner says that it has a shallow root system and represents a danger to his house. The tree is surrounded by other trees and serves as a visual and privacy barrier and cuts energy costs in the summer. Is the risk of the tree falling a serious risk to necessate removal?  

Answer
10 % lean is not a real danger. Trees do not necessarily grow straight up. However, trees with a significant lean may indicate a problem. Look for cracked soil and exposed roots around the base of the tree which may indicate the tree has recently begun to lean. Leaning trees or large branches do not always indicate high potential for failure. If the lean is a recent change, the potential for failure is much higher than if the tree is a 'long-term leaner' and exhibits growth that compensates for lean (indicative of a strong root system).

High Failure Potential:

Freshly leaning tree with recent root-lifting, soil movement or mounding near base of tree.

Inadequate root support, > half of roots severed inside drip line.

Lean associated with unstable soils or cracks in the tree.

Leaning over a target with > 45?angle to the lean.

I would suggest that you call the local office of the State Forestry Agency and ask one of their Foresters to come take a look.They should be able to advise you after seeing the trees and the situation. But from what you have said I would not think the tree is a hazard.