I live in Santa Fe, NM at 6300 feet elevation. We bought our current house 5 years ago. It has several mature aspen trees. We have three aspen trees in the front yard, growing about 6 feet away from the house. Their trunks are about 6 to 8 feet away from each other. The tree in the middle is healthy, big dark green leaves, but the two on the left and right have very small, much paler green leaves. I have no idea how old these trees are. What could be causing the two outer ones to look so different from the middle one?
Aspens Trees need a slightly acidic soil to grow and thrive.
You can test the ph with a meter to see if this could be the issue.
You may also want to familiarize yourself with the growth rate and pattern of these trees, since they are very near your home.