Dr. Alex Shigo found that trees and shrubs grew better, and healthier, in soils that were dominated by fungi and were as a result more acidic. These soils had more woody material then vegetative, or denser material then the lighter stuff from the plants we eat.
Since it takes time for this to happen in the soil the sooner you begin to make the change the better for what you want to plant. Lay your woody mulch on the soil this fall.

Any area that has been shrubby or forested will have fungally-dominated soil. My problem in gardening has generally been trying to change such soils to a balance between fungi and bacteria. A lot of mulching and little input of fertilizer or finished compost will achieve fungal dominance pretty quickly - a couple of years at most.

If you use partially composted wood chips (Bark mulch is best), you will get quicker results for introducing fungus. Our soils around here are mostly fungus-dominated, and raspberries do great. If I were to plant another bed, I probably would put down wet newspapers topped with mulch or wet leaves in the fall, and then plant the plants the following spring. Weeds are a huge headache around here!

When we bought the house, the previous owners had laid down sheets of weed barrier and laid a very thin layer of black dyed woodchip mulch. No plants or anything, just a long, wide strip of mulch in a raised retaining bed, most likely to smother a lot of weeds. Considering the shape the rest of the grounds were in, this was the most effort they put forth on the outside of the house.

So we yanked up all the weed barrier and left the woodchips sitting there. There have been some weeds come back which I have been pulling, but I figure I can choke these out with a thick barrier of shredded mulch.

So I guess I will lay the mulch this fall, dig through it to plant next spring, then top up with more mulch. Within a couple years, the soil will change to fungally dominated.

One last point to address. Should I work the wood into the top couple inches of soil?

I don't think that I would work it in. You are then producing a nitrogen shortage.

Will a nitrogen shortage in the top couple inches affect raspberry and blackberry bushes? I don't know where those roots pull nutrients from... and I guess I assumed they were deep-rooted and so wouldn't be affected. Am I wrong?

Digging in wood chips over a foot deep helped my vegetable garden tremendously this year. Just add enough nitrogen fertilizer to keep the leaves green.

See the comments of this for the results of some test beds.
http://lowcostvegetablegarden.blogspot.com/2012/07/wood-chip-bed.html

Here is a link that might be useful: Wood and chip garden bed construction

In theory digging soil amendments into the soil is supposed to get them were they are needed quicker. However, that may also create nutrient shortages, for a while, when the Soil Food Web gets busy digesting that material to make it available to plants.
In the forest and fields, where Ma Nature is in charge, these materials are not worked into the soil rapidly, as we would do, but over time by the Soil Food Web , as they have the time and energy to do that. That process appears to work quite well for the trees and wild flowers that grow everywhere.

Holy cow, emgardener.

If you have gardens growing with THAT much wood in the soil, that deep down, I guess raking woodchips into the top couple inches isn't really a problem.

We have a patch of everbearing red raspberries, and I mulch these in the fall with about 8 inches of shredded maple leaves. This helps keep the weeds down, and the leaves disappear by the following fall. The raspberries are generally healthy and productive. I have to thin them or they will get overcrowded.

Brambles have shallow roots, but prefer neutral soil (at least more neutral than blueberries, somewhere 5.5 - 6.5 is good), so I wouldn't go crazy with the woodchips. If you have some there that have been decomposing, fine, but put down some well-draining soil with compost mixed in, leaf mold will work too, but it has to be pretty good rich soil since you're not supposed to fertilize the first year. Make sure they are kept watered, but don't let them stand in puddles.

Here is a link that might be useful: Cornell Bramble page