Yeah I have seen similar in leaf litter that has gone fungal. I think you'll find the wood chips with the most roots have white mycelium on and around them. It feeds the roots from the wood and the plant feeds the fungus.
I have seen people warn not to dig chips in, but only pile them on the surface. Digging them in may cause draw down of nitrogen in the soil for bacterial decomposition, so if you dig them in, you might want to dig in some manure or other high-nitrogen material at the same time. Placing them on the soil surface does not cause a nitrogen draw down because decomposition is primarily fungal.
Were your wood chips "raminal" meaning from branches less than 3" in diameter? There was an interesting post here several weeks ago on the subject. I downloaded several pdf's that were mentioned there, and it seems that tree trunks and branches larger than 3" are mostly lignin where the molecules are strongly bound together. Raminal wood chips (RWC) are full of lesser developed lignin, sugars, proteins, minerals etc. and feed the soil in very different ways. Highly productive in agriculture when added to the top several inches of soil. I plan on experimenting with it next year, not just using it as mulch like I did this year.
I've been looking for that post but cannot find it. Perhaps it was on another site. I hope I'm not breaking any copyrights by up loading the pdf's here.
Sorry but I changed the original file names so I could better manage them in my data bases.
Correct me if I'm wrong, but from those photos, your native soil appears to be heavy clay. In that case, the good effects you got from wood chips might not be from the wood rotting, but from the fact that you had a bulky material breaking up the clay and creating air pockets.
We love wood chips! We dig them in, use them on top, layer in the bottom of beds, layers in bottom of pots, we let them rot, use them fresh - we just use wood chips anywhere and everywhere. Have never had any trouble with the garden and the rotten chips build up the soil.
I guess if there is one problem I would note, it is that even the soil in our garden paths is rich and black and the weeds like to invade the paths. We put mulch in the planting beds so that smothers the weeds there but in the paths, we have to hoe or use vinegar or the blow torch.
Eh, I'm not so sure that RCW is science. Wood chips and wood chip sized wood definitely seems to have a positive effect on soil and plant growth, though. Makes me glad that my hugel beds are primarily smaller sized stuff and lots of spikey-woody sweet gum pods.
I cannot find the good photos of our main garden beds. But, this link shows some of the wood chip use in and around the upper garden. The raised beds are almost completely wood chips put there over the course of 5 - 8 years. We might have added a bag or two of soil but for the most part it is all wood chips. Some straw is added to the top at times.