I have sown shade tolerant grasses to mixed result. It starts out OK in the spring but as the denser canopy trees start filling out they don't grow great.
This year I'll focus my efforts on opening the canopy by cutting & girdling trees. I will plant nitrogen fixers to get things going like geoff lawton suggests. Some annuals and a fair amount of perennials too. Black locust seed is pretty cheap & with pre-soaking the germination rate is good. I'll let some seeds come from the back end of the animals or old hay.
I think the only annuals I'll plant will be forage radish/turnips to open up the hard pan.