Why aren't there big holes around the base of every big tree?

 Because those forest giants feed on air.  The wood you fell for furniture and fire was created out of the air blowing through the leaves and needles.  C02 was harvested for its carbon. 

You'll find a hole in a tree
but not a tree in a hole.

   Water and trace elements generally come from the dirt but the thousands of pounds of fir and teak and spruce were formed from air.

So, that's why CO2 is called plant food.    It's not a vitamin, it's the number one body builder.

If you like this thought, what about how heavy is a cloud?  A cubic foot of water weighs just over 62 lbs.  So, 1 inch of rain on a square foot of pasture weighs about 6.2 lbs.   1 inch of rain on an acre is over a quarter million pounds.  Those clouds usually dump on hundred or thousands of acres and don't immediately disappear either.