Has anyone heard this before?

[Bakersdozen]

In regards to a nectar source, "One flowering tree is equal to an acre of flowers".

[apisbees]

That is a pretty general statement, but it doesn't take into account the bloom time. The volume of flowers that a mature tree (fruit nuts seeds) I would agree is equal to an acer of flowers. The other part that will effect whether it is a good pollen and nectar source for bees it the longevity of the bloom. The bloom on the tree may only last 2 to3 days, weeds and crops in the fields can last 2 to 3 weeks. There are so many factors that go into determining the beneficial aspect of a plant for bee forage.

[Alleyyooper]

Stands to reason a tree in bloom can provide more for the girls than a acre of flowers.
Here in Michigan when the bass wood blooms you can smell it a long way off. One tree of 18inch diameter will just be loaded with the flowers from the lowest limb to the very top and as thick as soybeans in a 15 inch row field.

An acre of flowers if you were to put them all in one group would maybe cover a couple hundred square feet if your lucky. Also as we have it right now so dry many of the flowers don't have any thing to give the bees any way.

  Al

[Bakersdozen]

Someone at my local bee club was conversing with me and made that statement.  I explained I had never heard that before, but wouldn't it be nice if it were true. 
Apis, yes there are a lot of variables.  Living in the 'burbs, thinking up instead of out is probably more practical.