I have a huge poplar tree that I am worried is dying.Last summer branches just fell off for 3 weeks. Big and little branches. This summer I noticed that leaves on the tallest part of the trunk are small and light and sparse. And another branch of leaves coming out of the center also has small light sparse leaves. The outer branches have fill thick green leaves. Also one of the large main branches from the trunk is slightly turning yellow...or faded.What do I do?!?!