Answer:
I only exist when you are here. Where you never were I can never be.
I run smoother than any rhyme, I love to fall but cannot climb. What am I?
Part carbon, part water, I am poison to the fishes. Many falsely claim my name, I am the pause that refreshes. What am I?
After you go through a fall, I will take over. All life will stall, or at least grow slower. What am I?
I have roots nobody sees. I am taller than trees. Up up I go but I never grow.
In birth I spring forth, in life I unfold. In death I wilt and die, but rebirth restores all.