It may not be stressed, it just may have reached adulthood. Regular cone production starts at twenty five to thirty years of age. Heavy crops are produced every three to four years in your area.
Your source who said it was stressed may also be correct. These are the factors that can stress hemlocks:
- if the water table has risen and is now closer to the surface
- if the amount of organic matter in the top layer has decreased. This is most likely in urban environments and goes with soil compaction from foot traffic
- dwarf mistletoe parasitizing the tree
- drift from applications of the herbicide 2,4-D
- insect attack - most insects attack the foliage: hemlock loopers, western blackheaded budworm and the hemlock sawfly are the most commmon
So, your diagnostic tools would be a walk around the tree to assess:
- is there adequate water but not water logged soil?
- is there any insect damage observed?
- any physical damage to the bark?
- any possibility of herbicide application drifting onto foliage?
- dig a small hole at least three feet from the trunk. How much organic matter is there in the soil profile. If you have more than two inches of rich organic soil the tree should be fine if all other factors are good.
More organic matter is always better. Top dress with a half inch of rich organic matter twice yearly, spring and fall, from the trunk of the tree to the drip line. Repeat every year and you will help your tree achieve a long life of over three hundred years.