A Riddle

Acorns to oaks
Owls call me home
I divide and divide in search of light
I live in the earth, and in the sky
Cause water to run up-hill
Leave without ever arriving
And wear my rings on the inside.
A slow-motion explosion
Of green (except when I'm not)
Boats sail on me
Cities stand on me
Common and rare
Deep and shallow
Tall and short
Broad and narrow
I am part of the furniture
I am fuel, I am fire
One summer umbrella
Above all - I inspire.
What am I?