New pine needles are produced every spring and summer and the older, less efficient needles turn brown and drop off. New needles last for approximately 4 years, and as the tree grows the new needles are located at the branch ends.
Evergreen needles change color in the fall just like deciduous trees. Even though pine trees are classified as evergreens their needles do not last forever. Spruce trees keep their needles for approximately 5 to 7 years, which is slightly longer than other conifers. While fall drop is a normal part of the lifecycle of an evergreen, some stress factors can intensify the fall needle drop, including drought, root damage, insect damage and herbicides.