Seeing signs of stress and or decline early enough can save your trees. Douglas Fir tees have a few tell-tell indicators of just how they are feeling and are easy to read.
Douglas Fir branches have a turned up tip, I always called it a smile and if they are not smiling then something is askew. Sometimes the heavy new growth will weight them down for awhile in the early summer but the rest of the year it should be a smile.
Douglas Firs will have cones on cycle of about 6-7 years apart, if you have cones more often than that it could be stress seeding, the last of their energy is spent on making seeds. It make take a year or two for ou to remember to notice it seems the cones are constant. The way I can check on a site visit is if I see brown cones from last year and then there are green cones from this year…not a good sign.
Compare the color of the foliage to other Firs in the area, Douglas Firs should be a dark green not yellow or light green.
Needle drop or needle cast us Arborists call it, heavy needles on the ground and bare looking branches, again compare to other Douglas Firs.
Hope these tips can help you feel better about knowing the trees around you, if you see any of these signs call a Certified Arborist, like me, to come have a look.