According to this, Rep. Rob Bishop thinks the Department of the Interior in both the Bush and Obama administration has suppressed two studies showing the damage that illicit traffic is doing to public and other lands on the border:

The first, from 2002, was a threat assessment for such places as Organ Pipe Cactus National Monument, the Cabeza Prieta National Wildlife Refuge and the Tohono O'odham Nation.

It concluded the threat was great indeed, both from the surge of aliens and drug smugglers who are "decimating public resources," and from the invitation the open border offered terrorists...

The second study, from 2004, looked at how the open border impacted Sonoran Desert wilderness in southwest Arizona, mainly Organ Pipe. This picture was equally grim—for the land, for endangered species and for the whole concept of border wilderness.

Both studies noted that the Border Patrol policy of blocking entry around cities and border ports pushed this illegal activity into remote areas.

Taking advantage of natural defenses isn't a bad thing, but in any case, the link goes in to attempts by both Tucson Weekly and Bishop to obtain the reports and getting the run-around. It also references this November article about conflicts between Interior and the Department of Homeland Security over the virtual fence and DHS operating on NPS land, and this video where Bishop presses Ken Salazar on the reports: peekURL.com/vgyp7x5