Trees are sparse, rarely forming natural groves, and it has been argued whether native Easter Islanders deforested the island in the process of erecting their statues, and in providing sustenance for an overpopulated island. Experimental archaeology demonstrated that some statues certainly could have been placed on "Y" shaped wooden frames called "miro manga erua" and then pulled to their final destinations on ceremonial sites. Other theories involve the use of "ladders" (parallel wooden rails) over which the statues could have been dragged. Rapa Nui traditions metaphorically refer to spiritual power "(mana)" as the means by which the moai were "walked" from the quarry. Recent experimental recreations have proven that it is fully possible that the moai were literally walked from their quarries to their final positions by use of ropes, casting doubt on the role that their existence plays in the environmental collapse of the island.