What's wrong with these trees?

That isn’t just how they shed? :P

By far, the most likely explanation for this browning is that the conditions are not allowing the plant to get enough moisture. Conifers are generally hungry and thirsty. Browning often occurs when the roots are not taking up enough water, and when the plant is exposed to cold drying winds – stopping the plant taking in moisture through it’s greenery. Remember that the natural habitat of conifers is very mild damp woodlands, where protection is in vast numbers, and the climate allows for plenty of moisture.
Have a go at resolving this issue first, although you will find that it will be a good year or so before it recovers.

There are other problems that could cause this – but with the info given, I’d probably go with that.

but it could be due to “Conifer Die Back” . Not likely unless you’ve trimmed them to much.

@Xilas Not doubting your advice on this tree, but many conifers live in dry areas. That’s why they can survive higher in the mountains than deciduous trees.

I lost a lot of pines one year due to bag worms. I can’t remember how the trees started to go but I remember seeing the bags all over the trees. I had to have them sprayed 3 or 4 years in a row to take care of the problem.

Do you see any sign of critters on them?

It can also be lack of sunlight. If you are losing the needles near the trunk, but not toward the tips of the branches, this is normal for some conifers (such as Austrian Pine Trees). As they grow, their branches stop sunlight from getting to the center, and the needles are no longer needed there.

Everything said so far is correct, and could be the cause of your problem. The way that the browning seems localized to just a few areas makes me think it is some type of pest. Problems with water or sunlight should show up all over the tree (and still may if this is just the start), but for now it seems to be only affecting a few spots. I’m not sure what pests there are where you live (Beetles, Bag worms, etc.), but that is what I would advise you to investigate.

I would have an arborist come out and take a look. There are several fungal infections that conifers can get that are specific to the type of tree. An arborist can both give a diagnosis and a possible solution.

Could be Bark Beetles I have seen this alot in local mountains in SoCal.

Where do you live? How old is the tree approximately? How long has it been in the ground? Where is it planted (i.e. near a house, in the middle of lawn, in between two houses, etc.)? Where did you get the tree? Are there any signs of insects entering the trunk and/or limbs, for example, holes from a boring insect or recent accumulations of pitch/sap on the outside of the tree. If a tree is attacked by insects, it will try to defend itself, which is sometimes expressed externally through “pitching out”. Insects can sense a stressed tree (which in nature is often times caused by a lack of resources, usually due to increased competition for these resources). What other vegetation is planted around the tree? Not cleaning up the leaves of deciduous trees sufficiently in previous years can increase the likelihood of fungal development. If you know the species of the tree, check the sunset hardiness zone. Maybe the climate is just not right for the tree. The sunset western garden book can provide a lot of valuable infomation on the requirements of a species of plant. Maybe this is typical of this species of tree. Or bring some samples and/or pictures to your local nursery, which will probably be cheaper than consulting an arborist.

If it’s a common problem, your local agricultural extension or city/county gov’t would probably recognize it in an instant.

It’s either shifting soil problems from either too much, or not enough water or you might need a fungicide, it’s hard to tell from those pictures and I don’t know where you live.