It's not unusual for evergreens to go through cycles of browning. You might want to call a local tree/shrub service.

It would be highly unlikely that the pine needles cause the browning of the needles of these other evergreens. Look closely to see if this is the results of some mechanical damage (something ate the bark off some of my Yew branches last winter that cause those branches to die back), lack of sunlight, lack of sufficient moisture.
It can also be just a normal thing since many of the needled evergreens do lose previous years needles after this years have grown out, so if the needles in the back are turning brown that might be normal.

the needles in the back of what?

Evergreens do shed their old needles, & many evergreens & other "needled" trees will shed needles due to heat stress in the summer;

Every July & August, my dearly beloved bald cypress trees look like they've been hit by a blowtorch, but they do recover.

You might check with your county agricultural extension office for guidance.

Best luck!

I am curious about pine needles as a mulch. There are eastern white pine groves in the area so I have access. What is the collective opinion of pine needles as a compost? Thanks ... DG

Down here in the southeast, pine straw from the Longleaf and Loblolly pines is the premium mulch.

Its light and the surface dries quickly. It smothers weeds well, but water passes through easily.

Its main drawback is that it is highly acidic.

I'm not sure if white pine needles share these qualities or not.

Here in the SE, pine straw, as it is called, is a very popular mulch. It is especially useful on hills as it will not roll down the hill as pine bark or some other mulches will. It breaks down easily and can give some acid to the soil.

Is your question regarding using the needles as a mulch or composting them? The functions are quite different :-) Pine needles or pine straw makes an excellent mulch, especially for woody plants. They are also a perfectly good addition to a compost, however they do take time to break down as their waxy surface or cuticle resists fungal or bacterial intervention. It's best to shred them or chop them up to speed up the process if you add them to the compost.

I should've elaborated, gardengal. We recently visited a nursery that was having remarkable success growing lady slippers - some native, some not. The owner attributed much of their success (keeping in mind that they're located firmly in zone 3 and have no greenhouse) to mulching. That mulch could be lifted in foot and a half or two foot "sheets" and it appeared to be mostly pine needles. I've used pink bark as a soil amendment successfully for years but I came away from that nursery thinking that I should be paying attention to what I'd just been shown. BTW, we grow slippers also.

Every needled evergreen will have the older neeles, behind the newer needles ie. in back, turn brown after the new needles have grown enough to be the primary source of nutrients by photosynthesis because those needles in back do not get enough sunlight to do that anymore and these fall off the tree and make those piles of pine needles that are under the tree.
Pine needles, no matter which evergreen the come from, will be acidic but will not significantly change your soils pH. They do not add acid to your soil.

Pine needles, no matter which evergreen the come from

I would hope it to be obvious, but pine needles come only from pines :-) Other conifer needles can be used as a mulch but pine needles are the largest, are shed relatively heavily on a routine basis and have other characteristics that make them a very desirable mulch product. They tend not to wash or blow away easily or migrate easily from planting areas to lawns like bark sometimes does. They do not mat together but remain 'fluffy', allowing excellent water penetration. And they are one of the best mulches for weed suppression......weed seeds fall through the pine straw rather than it providing a fertile seed bed such as compost or fine bark will.

If you have 'em, by all means use 'em! White pine sheds its old needles each year (most other species hold theirs 3-5 years) so if these trees are plentiful in your area, they can be a great source of a very inexpensive and superior mulch.

My Red Pines, Austrian pines, and my white Pines, as well as my spruces (which many people do call "pine" trees) and the Firs all shed last years needles when those that grew this year are able to function as they should.

Look closer - Austrian and red pines hold their needles for 4 years before shedding them. Spruces (which only folks who don't know trees call 'pines') hold their needles for 5-7 years before shedding as do firs. All conifers shed older needles but because the shedding is usually gradual it is not nearly as obvious to the casual observer as it is with white pines, which actually appear to go through a fall color change when they lose needles each year. Broadleaf evergreen shrubs also go through a similar process of shedding older, interior foliage periodically.

downeast gardener, I am also a downeast gardener. Pine needles, which I use to mulch around my house, can be found bagged up, and in abundance, at the landfills in the fall.

kimmsr, the people who call spruce trees pine trees are the same people who call apple trees peach trees.

That is quite true, but there are many people out here that do that and I seldom disabuse them of that. Implying that someone is stupid because they do not know what they are talking about is usually counterproductive.

Hello annpat! Not mentioned here is the most prolific source of conifer needle mulch (being as PC as possible here) of them all. 100% drop annually. Locally, annpat and I call it hackmatack but outside of Maine it is known as tamarack or American larch (Larix americana, I believe).

I have a pretty little hackmatack right outside my bedroom window, but if I want a needle mulch (and I do!), I get my foolish neighbor, Phil, to give me his pine needles.