This is a most fascinating verse because it so clearly comes as part of a discussion of the Lehites. The specific reference in the allegory is to the Lord clearing ground for the transplanted branches. Botanically, this certainly refers to the removal from the area of the plants that would compete with the branches for nourishment.
Translated into history from the veiled terms of allegory, this is the only absolute reference to a population existing in the New World prior to thee arrival of the Lehites. Just as Israel entered its promised land, and needed to "unencumber" their ground, so is it implied that the Lord has done the same for the Lehites. Of course we have no indication of how this clearing occurred, but every other part of the allegory of the Lehite "branch" has had reference to a discernible historical fact, there is no reason to presume that this particular reference does not, particularly since there is no literary argument that requires this verse above and beyond the reporting of the fate of the Lehite branch.
The irony is that the clear statement that others would be in the land when the Lehites arrived (and would be "cleared" so as to make place for the Lehites) comes in ancient prophecy rather than current records. Zenos tells us, but Nephi does not (explicitly).
Another possible reading of this verse is that all previous peoples will have died out, and that the reference is to the Jaredites. However, the Jaredites lasted until after the landing of the Lehites, and therefore were not "cleared" from the land for the "planting" of that branch of the house of Israel.