Attempting to establish any kind of game crop beneath the deep shade of woodland is doomed to failure. Even if the canopy is opened up to provide sufficient light competition from tree roots is a big problem. It would also be quite wrong to risk damage to the conservation value of any natural woodland ground flora that may be present in the crop establishment process.
However, game crops do have an important part to play in newly planted woodland. Where winter cover is required in the years before the trees and shrubs have become well established. Where new woodland is planted on arable sites it is often helpful to sow a game crop and then plant the trees into it. Alternatively, providing suitable small machinery is available, the crop can be sown between the tree rows, preferably by drilling rather than broadcasting.
Perennial crops such as Canary grass are useful in this situation as annuals become progressively difficult to establish as trees grow. Biennial crops such as kale are also useful, particularly as this crop will often still provide some cover after three or four years.