Orchid XP v8 wrote:
>> I would suspect that there is something in the groundwater, either 
>> something directly harmful to the tree (weedkiller) or something bad 
>> for the fungus that all tree roots rely on.  If the water tests okay 
>> then possibly the ground around the tree is getting compacted so that 
>> the roots can't get enough oxygen or water.
> 
> ...or maybe it's the fact that, you know, 80% of the tree's rootsystem 
> is under concrete now and doesn't receive any water. ;-)

The fact that the surface is covered by concrete by no means prevents 
the roots underneath from receiving water.  Groundwater will move from 
underneath open areas where rain falls to underneath paved areas where 
the rain does not touch.  The water table can and usually does remain 
underneath paved areas, and as long as the tree's tap root can reach the 
water, all is fine on that score.

> Or maybe it's the fact that the sun only shines directly on the tree's 
> leaves at noon. (I don't know how much sun oaks require.)

Oak is shade-tolerant during its early stages (they're growing quite 
well in the pine grove my father-in-law planted twenty years ago), and a 
mature oak in a forest often receives sunlight only from directly overhead.

Regards,
John

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