Pine needles in mulch
The above article and the discussion mankes no mention of pine needles but certified arborists who have made this product available should insure this will not be a problem. You did not specify what the mulch would cover but it should be a useful inert ground cover or plant insulator.
Mulching serves a couple of purposes. First, it helps control weeds and second, it helps moderate soil temperature and reduces moisture loss. This insulating feature is very important in Oregon as it helps plants from freeze/thaw cycles in winter, especially if the plants have been recently transplanted and are still establishing a good root system (2-3 years). If you already have a good layer of mulch down, 3-4", then you don't need to add more but if your mulch layer is thinning or there is none then yes fall mulching is good. We recommend that you do not mulch until late November or early December as it is important for the soil to cool down so the plant shuts down for winter. Mulch should not be placed directly against stems or trunks of perennials, shrubs and trees.
Thank you for the quick response. I had to laugh...it was the arborist who suggested that I ask you. The information that you furnished is most useful.