Ask Americans about the pedestrian fencing and vehicle barriers along the Mexican border and brace yourself for a torrent of opinion.  Some will say they’re necessary; others will say they’re ugly.  Some will say they’re an effort to stem massive law breaking; others will say they’re symbols of an immigration system in collapse.

Few will say they benefit the environment.

But, in important ways, they’re doing just that.

The best laboratory to judge their impact is heavily-crossed Arizona, with its vast tracts of federally-managed borderland.  These desert and mountain ecosystems are unique in the world, and extremely fragile.  They’re also remote and sparsely populated, making them ideal smuggler terrain.

After a multi-year planning and construction effort, opposed by powerful environmental groups such as the Sierra Club, vehicle barriers now block most of the land where these preserves meet Mexico.  The result has been a significant drop in the number of destructive smuggler drive-throughs.

A good example is southern Arizona’s Coronado National Forest, which has Normandy-style barriers on its border land, excluding the mountainous areas.

“The smugglers have a much harder time driving their loads in and that has benefited the land,” says Keith Graves, a former district ranger for the Coronado.  “We’re not seeing the kind of damage we used to see.”

The same has occurred at the 330,000-acre Organ Pipe Cactus National Monument southwest of Tucson, where Manager Lee Baiza calls its rail-on-post barriers the best investment the Department of Interior has made in a long time.

In addition to making it tougher to drive across the border, the barriers have reduced the number of southbound chases.  In these episodes, smugglers spotted by law enforcement would turn around and flee, tearing up the desert as they escaped back into Mexico through the old wire fence.

At the 118,000-acre Buenos Aires National Wildlife Refuge — where vehicle barriers were installed in 2006 and replaced by a four-and-a-half-mile pedestrian fence in 2008 — vehicle crossings have been virtually eliminated, says spokesperson Bonnie Swarbrick.

The Buenos Aires is one of the few federal preserves with a significant stretch of pedestrian fencing, which most land managers reject as too intrusive. Unlike vehicle barriers, an impassable wall can alter the migration of animals, some endangered, possibly blocking their access to key habitat on both sides of the border.

In areas where pedestrian fencing does stand — Arizona now has 124 miles of it and 183 miles of vehicle barriers — ranchers and landowners report improving conditions on the fence’s north side — less ground trampled by people and grazing Mexican cows, less trash to poison animals and foul water supplies, and fewer foot trails and wildcat roads.

Both can cause serious erosion.  If used often enough, they denude the ground of vegetation and compact the soil, allowing water runoff to make gullies that can form their own streams.

Roads provide paths for predators to move into new areas to feast on prey species, throwing animal populations out of balance.  A smuggler also has no concern for the archaeological sites he’s rolling over or the endangered plant species he might be damaging.

And to avoid detection, he necessarily drives through the most rugged terrain, which means the vehicles often break down, becoming litter.  Land managers find big pickup trucks upside down in stream beds, leaking gas fouling the water supply.

The number of abandoned vehicles at Buenos Aires stood at 100 a few years ago.  Today, there’s one remaining with no new ones arriving, says Swarbrick.

At Coronado, rangers now find only two or three abandoned vehicles a year.  “Before the barriers began going in 2006, there were 60-70 a year,” says Graves, now a liaison between the Forest and the Secure Border Initiative program.  “Removing them caused more damage and sometimes we had to leave them there because getting them out was impossible.”

No one argues vehicle barriers are foolproof.  Smugglers have been known to ramp over them and use torches to forge openings.  And even land managers who support the barriers understand they can be a doubled-edged sword.  The act of getting construction crews and equipment onto these lands to install them itself causes damage.

In addressing the tradeoff they face, land managers note it isn’t just smugglers who make wildcat roads.  In chasing down illegal crossers, Border Patrol does as well, and the damage is the same.

At western Arizona’s 860,000-acre Cabeza Prieta National Wildlife Refuge, the reduction in cross-border vehicle traffic has done little to reduce the network of illegal roads, which now total 8,000 miles, according to a recent mapping.

Many of the newly created ones have been made by Border Patrol chasing illegals moving north on foot.  Even so, Cabeza’s manager Curt McCasland says positive things happen on the land when Border Patrol controls it.

“I can send folks out into the desert now without worrying about them getting run over by all the illegal traffic running through the middle of the refuge,” he says. “In 2002 and 2003, it was like the wild west here.  But the downside is that sometimes the cure can be as bad as the disease.”

Along with other land managers, McCasland is working with law enforcement on a strategy that involves less off-road driving — such as putting more Border Patrol on the border, in preventative mode, rather than dropping back and chasing smugglers and people around deep within the refuge.

“If we were able to deter illegal traffic from occurring here in the first place, we’d be protecting this place much better than we are now with reactionary interdiction,” says McCasland.

But Border Patrol only came onto the land in force because the smugglers did.

Beginning in the late 1990s, the movement of people and drugs across Arizona’s borderlands exploded, demanding a response.  It came when the Bush administration, through the 2005 Real ID Act, gave the Homeland Security secretary the power to waive environmental laws to get border fencing and barriers built.

Matters had grown desperate at places like the Cabeza, where then-manager Roger Di Rosa was telling reporters the refuge was a war zone.  The chaos was repeated at Organ Pipe and at Buenos Aires, which takes up most of the Altar Valley.  At one point in 2006, foot crossings in the Altar reached an astonishing 3,000-4,000 every 24 hours, and smugglers in trucks made mad runs across refuge land.

Don’t misunderstand.  Arizona’s borderlands are still fighting the smuggler wars.  But in small steps aided by barriers and fencing, conditions are improving.

More than two years ago, 94 percent of Organ Pipe was closed for safety reasons.  The figure today is 55 percent.  The pedestrian fence at Buenos Aires has significantly reduced foot traffic in the valleys, forcing most walkers into surrounding mountains.  Mexican cattle and sheep can no longer enter refuge land to graze and some illegal roads are beginning the slow process of repairing themselves.

Buenos Aires also has land off-limits to the public, a parcel on the border representing 3 percent of its acreage.  Before the barriers and fencing went in, this ground was being pounded every night by illegals, until the Refuge manager closed it.

But this area, too, has begun to regenerate, a symbol of what might be a broader rebirth. “It looked like a no-man’s land,” says Swarbrick.  “The ground was entirely denuded of vegetation, discarded clothing, litter and water bottles lay everywhere.  But now there’s no visible litter and lush grass is back.”

Refuge managers will consider reopening the land soon.

Leo W. Banks has been a journalist in Arizona for more than 30 years. He has covered border issues for the Wall Street Journal, National Review, Tucson Weekly and others.