Windbreaks: Trees Vs. Berms

I listened to the latest podcast this morning (140) and was going along with everything until the part about using a giant berm instead of trees for the windbreak. I can definitely see how a berm would be extremely effective, but I think the numbers thrown out were something like trees might be 10% effective and berms might be 90% effective. Since I have 20 acres of very windy land, this is a topic close to my heart so I wanted to follow up and get some more of the pros/cons for each. I've been planning to put in a big strip of Norway Spruce to do this job on my land. I can't really imagine how I could make a 15-20 foot earth berm without causing major problems for the rest of my site, but I could be convinced to try a hybrid approach if the trees really are that ineffective. So, here's my tentative pros/cons list.

Pro Trees:
Tall -- norway spruce grows 110-130 feet high, which seems like it would provide a much bigger wind shadow
Cheap -- total cost will probably end up being around $100
Reversible -- If I change my mind I can cut them down and go a different route
Low input -- doesn't require extensive use of heavy equipment, can be done by hand

Con Trees:
slow -- they take years to get big
vulnerable -- it'll basically be a monoculture of trees, some pest could come in and kill them all, tornado might poke holes in my plans
effectiveness? I'm looking for clarification here. In my limited experience, evergreen windbreaks seem pretty effective. Is there more to the story?

Pro Berms:
Effective -- 100% certain to block wind like crazy
Lots of opportunity for microclimates/interesting slope planting
Permanent -- it might still be there when the sun burns out.
Relatively quick -- with enough tractor power, the berms could be built in a short time compared to growing trees
Could be made with hugelkulture.

Con Berms:
Cost-- It seems like it would be incredibly expensive to either do that much earth moving or have that much material brought in
Permanent -- if you find out it was a mistake for some reason, it costs just as much or more to get rid of it
Bunkerlike -- I think it might make the place feel like some kind of walled off bunker compound
Destructive to site -- All that tractor work... it's going to have a huge impact on the land and existing plants/animals

On my site, trees seem like the clear winner (mostly on the cost angle, considering how much it costs to get a pond dug, I can't imagine what the berm would be for a 700 foot long 20 foot high berm). What do others think about the relative merits of the two?

I'm no expert, but the best luck I've had with windbreaks is piling up tree tops and limbs to make a sort of 'brush berm,' and planting trees behind those to protect them from the wind. The brush berm shrinks with time (and birds nest in them), and the trees grow to take their place with a sort of hugel-bermish thing decomposing right there to feed them.

*I haven't listened to the podcast* so I might be making a totally irrelevant argument, but...
All the info I've come across recommends filtering, rather than blocking wind to avoid turbulence. 50% blocking is the usual figure.
This link mightn't be that helpful, but it gives an idea: http://www.fao.org/docrep/T1765E/t1765e0t.htm

Leila Rich wrote:*I haven't listened to the podcast* so I might be making a totally irrelevant argument, but...
All the info I've come across recommends filtering, rather than blocking wind to avoid turbulence. 50% blocking is the usual figure.
This link mightn't be that helpful, but it gives an idea: http://www.fao.org/docrep/T1765E/t1765e0t.htm

I'm with Leila. I haven't listened to the podcast, and I believe that less than a solid wall is a good bet. too impermeable, and the wind just goes up and over and right back down again, sometimes with worse effects than nothing at all.

Leila, thanks for that link, very good info. It looks like what they're saying is that a semi-permeable windbreak will slow the wind significantly for a long distance out (10 or so times the height of the windbreak), while an impervious windbreak will slow the wind much more, but over a much shorter distance. It's also making me rethink my species choice; I don't think Norway Spruce will regrow well from stump sprouts, which would make maintenance of the windbreak problematic over the long term. The trouble is that some of our worst winds come through in the winter months, sucking the heat and moisture out of everything they touch (including my house). Anyone know of some good evergreen species that respond well to coppice management?

i'm of the thought that berms alone would cause really bad effects downwind as they don't just break up the wind but redirect it downward similiar to a solid wall.

I think the best solution could be a combination of both,however, you are right about the cost. Only build a berm if you have the equipment, materials and time, otherwise put in those fast growing trees and maybe protect them with a faster growing perennial like Jerusalem Artichokes until they get growing.

swirling winds from a berm alone could be far worse than just say the Jerusalem artichokes alone..and if you are near someone growing J A's you probalby can get some starts for free or cheap