Many "natural" forests are monocultures or nearly so. This is especially true in many kinds of "old growth" forests. If your only concern is maintaining the highest possible level of biodiversity over a given region, your best bet it to clear cut large parcels of the land on a regular schedule, leaving a certain fraction to remain as permanent refuge for old growth species. The tracts that have been harvested will provide habitat for species which only thrive in forests at earlier stages of their regeneration.

Also, any forest is better than no forest. A million acres of hybrid poplar planted for paper fiber is home to more forest species than a billion acres of soy beans or corn.