Answer: It is natural for pines to yellow and drop their old needles, usually at the end of the growing season, just like deciduous trees drop their leaves. Did you ever take a walk in the woods and notice the thick layer of pine needles underfoot? As for your trees, if other Norways in your neighborhood did the same thing, and it wasn't an inordinate amount of needles, it's probably not a cause for concern. Without more detail, it's hard to determine what the cause is, but if you had an unusually dry summer, being stressed for water may also cause some needle drop.
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