Growing Things: Maintain moisture to prevent spruce tree needle loss

Q: I was hoping you could help me. I have a row of spruce trees which are about 40 years old, and I would guess over 50 feet tall. I planted them when they were about a foot tall. I realize it is normal for them to lose needles in the interior of the tree, but over the last few years there has been an excessive amount of needle loss. In Strathcona County I have noticed this happening to other spruce trees, resulting in them dying, and I am very concerned that this will happen to mine. Can you of