Juniper trees exude the allelopathic compounds from their
roots.
The other concern many have is the acidification of soil by juniper chips, this is a minor concern in reality, the needles will give more acidity than the wood chips.
I usually recommend keeping juniper wood chips to paths unless you first
compost them
enough that they begin to turn a brownish color, but that is mostly so you don't put the sap on the soil.
Junipers, like pines, have resinous sap that will burn quite well, because the sap contains the allelopathic compounds but in smaller quantites it becomes prudent to let the wood chips age at least 6 months before using them in garden areas.
It is more a play it safe thing over a must do thing though.
If you have an area you want to plant blueberries or serviceberries in, then that would be a great place to use the needles as mulch or even dig them in the top six inches of soil.
Redhawk