Which of the following would be the best way to restore a forest to its natural state and increase the biodiversity of an area that had previously been logged for paper?

Till the area and plant agricultural crops.
Replant the area with slash pine seedlings.
Repeatedly burn the area to kill weed seedlings.
Encourage the regrowth of native plants.

Encouraging the regrowth of native plants would be the best way to restore a forest to its natural state and increase biodiversity.