There are a couple of things that could be happening to your tree. Every year, usually in the fall, pine trees shed some of their oldest needles. The needles turn yellow or brown before they drop off. This is most likely what's happening to your tree. Alternately, the tree could have a foliar disease. It's not possible to diagnose this problem without having a sample. We'd suggest that if you're seriously concerned about the health of the tree, you bring in a sample branch for our diagnosticians to look at. There is $7.00 charge for this service. Our office is located at the Boulder County Fairgrounds at 9595 Nelson Road, Longmont. Ann