Don't do it.
I don't know if this is just a wives tale or true, But I always heard there is something in pine needles that stop seeds from germinating. I think that's why they make great mulch.
I think just about any organic matter is good for your soil over time.

Check out the compost forum but be for warned....They are all admittedly Whackos. lol
:)Laura

I always wondered why nothing grew under the pines! I copied these-don't know if its helpful or not!

The birds would love your tree for shelter. Turn it into a buffet for them by placing fruit slices, seed cakes, and suet bags in the branches.

Cut off the boughs and use them as protective mulch around perennials and small shrubs. In the spring, use the large branches to stake peonies and other floppy flowers.

Dry the branches, crumble the needles, and mix with cinnamon sticks to create potpourri.
-B

If you have azaleas or rhododendrons, they will loooove it if you spread some pine branches under them. It's a great way to give them the acidity they need.

That's what it was -- lightbulb moment -- acidity, which I need for my azalea bush.

Pine needles make great mulch. Nothing grows under them because it falls so thickly under the trees and blocks everything. I have used it as mulch in my flower beds and it is breaking down very nicely. It does add acidity to the soil and is supposed to be an excellent mulch for azalea's and strawberries. I'm using it in my lasagna garden too.
I've been shoveling it from around a very established tree at my Mother in Laws and the bare spots are starting to grow lawn again now that I thinned it out. So it doesn't stop the soil from supporting plants.