The cause is likely root disturbance & damage along with soil compaction from heaving equipment being moved over the ground during construction. When soil gets compacted, the oxygen from the soil is lessened because it is literally being squeezed out. This lack of oxygen can cause stress to the tree & often time death.
Many times, the full effect of construction work can last anywhere from 5-7 years. Because of this, it is important when planning any construction near trees that the critical root zone of the tree is considered. If you are going to be operating very heavy equipment near a tree, it is best to determine ahead of time if you think the tree can be saved or if it will become a causality of construction. There are other factors to consider, but the critical root zone is basically the drip line of the tree. No construction activity should occur within that drip line of the tree canopy. If you remain unsure, please call Hansen's for a certified arborist to take a look at the trees at your desired location.