One observation from the experiments I conducted over the past two years is that hemlocks show considerable variation in their ability to retain needles in times of stress. This picture illustrates it perfectly:
These branch cuttings were all collected the same day and handled similarly. They were cut from different trees, placed in water tubes, and kept in a shaded location. I took this picture six months later. You’ll notice, when it comes to retaining needles, the ones on the left have far more tenacity than the ones on the right. This was not what I was looking for, in fact it was a complicating factor. But I found it very interesting.
I guess in some ways people are like hemlocks. Everyone handles stress differently.