I'm looking to plant some trees in the spring for a windbreak. I'm looking at White Pine or Norway Spruce. The DNR website states these trees will have a mature spread of 20-30 feet. They recommend planting trees 8 feet apart in rows 8 feet apart. That seems to be pretty crowded to me. Is that going to result in a healthy windbreak ? What are your thoughts ?

It'll take a few years to fill in, and it will be thick when they grow together, that's what you want, you can always take every other one out eventually.

Wisconsin coop ext has great info on wind breaks. I used their info and Penn State's to design my wind break. I used Norway spruce, hybrid poplar and native shrubs.

I assume you're looking at enhancing wildlife vs a wind break for soil erosion, if yes- your tree selection is a good one. For wildlife I plant 4-5 rows deep, starting the first 2 rows with shrubs that create a snow trap, rows 3-5 are white pine and white spruce, my stem count is predicated on an 8' spacing.