Bonsai Dryads

Dryads hatch from acorns. Some wicked folk kidnap newborn dryads, and bind the acorn in such a way that the dryad hardly grows. This means that when they reach adulthood both their human and tree forms will be tiny (about the size of a human hand) and stunted. Such creatures cannot reproduce, since there is no way to create fauns of the same size.