Looking to the interior of your evergreen tree, you may see yellow or brown needles for the first time. People who have grown evergreen for years have discovered that this is a normal occurrence for evergreen. After years of new growth, the evergreen will release some older needles toward the interior of the tree.
A pine tree, as one type of evergreen, will usually drop needles in the fall at the end of its second season and then repeat the process every two to three years as it grows.
So if the needles are green and supple at the end of branches, there is no reason to be concerned about the falling needles from the interior of the tree. Let the fallen needles remain on the ground beneath the tree where they can decay and subsequently provide nutrients to the tree.