Tarp on ground next to tree?

I've got an area around a tree that has refused to allow the grass to grow. Today I noticed the area was very moist so I decided to take a rake and turn the soil so I could try again with some seeding.
I found a tarp on the area underneath the dead sod. The guy that installed the sod a year and a half ago told me he found a tarp and had given me the impression he would remove it prior to putting the sod on top of it. Obviously he has misled me.
Any ideas on why the former homeowner would put a tarp down over the tree roots and stuff? Makes no sense to me. The tarp covers about 25 square yards.
Thanks for any ideas you might help with.
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Might have been moldy and stretched out in the sun to bleach it out?
--

"Life should NOT be a journey to the grave with
the intention of arriving safely in an attractive
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What kind of tree is it? Maybe to catch nuts. Maybe quick clean up after the leaves fall.
--
Billy
Coloribus gustibus non disputatum (mostly)
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John wrote:

To kill grass and weeds unwanted there.
--
john mcwilliams

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We recomend just placing the mulch on top of the turf.
Mulching - http://home.ccil.org/~treeman/sub3.html and http://www.treedictionary.com/DICT2003/M/ Look up "Mulch"
Sincerely, John A. Keslick, Jr. Arborist http://home.ccil.org/~treeman and www.treedictionary.com Beware of so-called tree experts who do not understand tree biology. Storms, fires, floods, earthquakes, and volcanic eruptions keep reminding us that we are not the boss.
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