Answer: I can't tell for sure from your description, but Japanese Black pines can be host to leaf miner insects which can turn the needles brown with their feeding, and a fungal disease which turns the tips of the needles brown. And, root stress can turn the entire tree brown. I would check the soil conditions and the roots, and also inspect for insect populations. Or, you can cut a branch from the tree and take it to your local cooperative extension office for inspection and positive diagnosis. Helpful folks there can suggest control options. Best wishes with your trees!
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