IMO, at least in my area, hedges just 'happen' once interference (mowing, grazing...) ceases. In my area I expect Crataegus, Prunus, Sambucus, Quercus, Salix, Carpinus, Cornus, Fagus, Rubus, Rosa ... and so on to start showing up soon concerning the woody or rather woody plants. Results vary and of course depend on where you are. But leaving things and not doing a thing is, probably, leading to the most natural results while being the easiest and most sustainable.
I would like to add that personally I value 'naturality' over 'biodiversity'. Many natural habitats are natural monocultures and thete is nothing wrong with nature and no need for man to make 'improvements' here. Take Fagus forests as example. Those are very common in my area and the adaptions making the genus Fagus rather successful is that a) adults shade the area heavily b) they mulch heavily suffocating and further depriving competing plants of light and c) saplings require much less light than many other trees saplings.
In any case the plants listed above might provide a good solid woody basis for a hedge in your climate if you want to speed things up or force it a certain way.