The Science
Cows, a non-native species: do they belong on public lands?
Many of the ranchers in this story believe that the environmental groups end goal is to have cows removed from all public lands. They feel defensive because of this.
There is some truth to it. Robin Silver and the Center for Biological Diversity believe that there is no place for cows on public lands in the arid West.
“There is no place for a cow, particularly on public lands in the arid West,” said Silver. “That’s just nonsense. That's just a function of culture and archaic politics.”
This belief is rooted in the fact that cows are a non-native species in North America. They were brought here with the first European settlers hundreds of years ago. Technically, cows are an invasive species, and like other invasive species, they’re damaging to the ecosystem when not kept in check.
“These ecosystems didn’t evolve with cows,” said Elizabeth Makings, the Collections Manager at ASU’s Herbarium. “So they’re not really equipped, they’re not as resilient when you get these enormous animals in there that consume a lot of vegetation and trample and compete for resources with the other wildlife.”
While Silver believes that there is no place for cows on public lands in the arid West, it’s unlikely that this will ever become a reality. Grazing is one of the most pervasive uses on public lands. More than 250 million acres of public lands are used for grazing every year.
“If you look at why we have so many endangered species in the Southwest, every one of them, every one of their demise is in large part due to cow grazing,” Robin Silver.
The San Pedro Riparian National Conservation Area
The San Pedro flows north from Sonora, Mexico into Arizona where it eventually ends at its confluence with the Gila River. It flows for nearly 140 miles through these desert landscapes.
It is one of the last free-flowing rivers in the Southwest. Many have called it one of the last wild rivers in the United States, and it's internationally recognized as a river of hemishperic imortance. This is because it provides food, water, shelter, and a pathway for millions of migratory birds, belonging to hundreds of speices, making their way north from South and Central America every year.
Because of this, the SPRNCA has become a bucket list destination for bird watchers around the world. In the 1990s, the American Bird Conservancy recognized the region as the first "Globally Important Bird Area" in the United States and said it was the "largest and best example of riparian woodlands" remaining in the Southwest.
The Audubon Society states that; nearly 45% of all 900 bird species in North America use the San Pedro river area for habitat at some point in their lives. Endangered Species such as the yellow-billed cuckoo, southwestern willow flycatcher, the northern Mexican gartersnake, Gila topminnow, and the Huachuca water umbel call the SPRNCA home. Even jaguars and ocelots have occasionally used the river for habitat when they venture this far north from Mexico.
Riparian ecosystems like the San Pedro river's watershed, are a hotbed of biodiversity in Arizona's arid climate. Only about three percent of the state is considered riparian habitat, but over 90% of the species in the state interact with these ecosystems in some way.
The San Pedro river is a very special place, but it's also endangered. In 2022, the organization, American Rivers, named it one of the most endangered rivers in America. They cited excessive groundwater pumping and pollution as the main threats to the river.
Because of its endangered nature, and rich assemblage of biodiversity, people have been trying to protect the San Pedro and its riparian habitat for decades. In 1988, the U.S. Congress designated the San Pedro Riparian National Conservation Area as its first Riparian National Conservation Area. The SPRNCA protects over 40 miles of the San Pedro River starting at the U.S. Mexican border in Cochise County. It protects roughly one mile on each side of the river and contains nearly 57,000 acres of public lands managed by the BLM.
While excessive groundwater pumping and pollution were named as the top threats to the San Pedro river as a whole, within the SPRNCA, cows are being pointed to as one of the biggest threats to the river. Advocates for removing cows from the NCA say that these large mammals are changing the vegetative landscape and threatening endangered species.
The last remaining populations of the Huachuca water umbel are being eaten and trampled by the cows. Some claim that just one cow in the river could potentially destroy the remaining populations of the Huachuca water umbel.
The SPRNCA's protected status and the river's lack of large diversion dams have made it an important research site for scientists around the world. In a 2018 letter to the BLM, 21 scientists wrote:
"Because of its large size and status as a conservation area, the San Pedro in the SPRNCA has become the most frequently studied river in the Southwest... Studies within the SPRNCA have, to date, yielded valuable information on the environmental flow needs of various taxa and ecosystems, the ecological importance of perennial and intermittend stream flows, and the importance of flooding as an ecosystem disturbance."
“The loss of the San Pedro, that’s huge," Robin Silver. "The San Pedro is basically the last of the surviving free flowing rivers in the arid west. So these are huge, historic legacy issues we’re dealing with now.”
The Impacts of Cattle on the SPRNCA...
In the spring of 2018, a group of 21 scientists wrote a letter to the BLM ahead of its release of the draft Resource Management Plan, urging the agency not to reauthorize cattle in the SPRNCA. The letter read:
“We wish to apprise you of what we- as scientists with experience and knowledge of the San Pedro River ecosystem- believes is at stake in the Bureau of Land Management’s planning process: if livestock grazing in the SPRNCA is reauthorized, not only will many aquatic and riparian species and ecosystem functions be jeopardized but the critically important role of the Conservation Area as an ecological reference site will be lost.”
The letter also pointed out that climate change made it even more imperative to remove grazing from the area.
“We’ve sent the BLM thousands of pages of science,” said Cyndi Tuell, the southwest programs director for Western Watersheds Project. “We’ve sent it to them many times over the years.”
There is a lot of scientific evidence showing that grazing is not compatible with riparian conservation in the SPRNCA. Tuell says she is shocked that the BLM has not taken into account all of the science done “for this specific spot on the planet, showing that cows are bad for this specific spot.”
So why are cows bad for this specific spot on the planet?
According to Dr. Juliet Stromberg and Elizabeth Makings, two of the scientists who wrote the letter to the BLM in 2018, cows change the vegetative landscape of riparian areas through their grazing patterns. This change in the vegetative landscape has a lot of negative impacts for the ecosystem.
“The cows are feeding on plants preferentially,” said Dr. Stromberg. “You have all of the grasses preferentially removed first and then once they’re gone, the cattle might feed on the cottonwood and willow seedlings. And so they’re shifting the vegetation to plants like salt cedar or prickly plants that are well defended.”
When the cattle selectively feed on grasses and willows, it affects the river by causing erosion and sedimentation. The ecosystem evolved to have grasses holding the soil in place, but now it is eroding into the river and changing the water quality and the flood regime.
Dr. Stromberg said that when cattle remove most of the grass from a landscape, it causes more erosion during monsoon season and more flash flooding. She said that the grasses in the SPRNCA evolved to work as a kind of “moderating sponge” for floods.
According to Dr. Stromberg and Makings, the cattle are also trampling the streambanks which leads to greater erosion and sedimentation. This is impairing the water quality in the river.
The cows are also causing mesquite and other invasive shrubs to take over what was once grasslands. Over grazing contributes to this, but so does the cows’ poop.
“Cows eat and distribute mesquite seeds,” said Tuell. “They disrupt the lands, and then make these little pockets for the mesquite and other invasive shrubs to grow. They don’t eat the scrubs unless they’re out of grass, and then you get these shrub invaded grasslands where the grasses are mostly invasive and highly fire prone.”
The mesquite and shrubs are something that ranchers and the BLM put a lot of time and energy into keeping at bay. The BLM has begun implementing vegetative treatments commonly called Spike treatments to try and mitigate the impacts that cattle are having on the grasslands.
A new survey from the Center for Biological Diversity
A survey released on April 10th, by the Center for Biological Diversity showed that 39 out of 41.9 miles surveyed of the San Pedro River in the SPRNCA have been significantly damaged by cattle grazing. The survey showed that the vegetative understory in the SPRNCA has been significantly depleted by cattle grazing. Trampling and cow feces along the river were also shown to have significantly impaired the ecosystem.
“We’ve essentially lost the entire San Pedro river understory because of grazing promoted and facilitated by cow-worshiping, rancher-fearing, BLM employees,” said Robin Silver, co-founder of the Center in a press release acompanying the survey. “Management of this fragile ecosystem should be transferred to the National Park Service.”
The Center said that the damage shown by this survey is particularly concerning for some of the endangered species that call the SPRNCA home. The sections of the Babocomari river in the SPRNCA that were classified as significantly impaired by the survey are critical habitat for the northern Mexican gartersnake and the yellow-billed cuckoo. These two species depend on a healthy understory along the river for habitat.
E.Coli contamination on the river
Another problem caused by cows in the ecosystem is E.coli. When too much cow poop accumulates in or near the river, it can cause excessive levels of E.coli to accumulate. This is a problem that has arisen specifically on the Babocomari allotment.
The BLM has said that the Babocomari river is now provisionally listed as impaired for exceedances of E.coli standards and there is a pending review from the EPA. Because of this, part of the lease renewal terms for the Babocomari allotment say that the lease can be revoked if the E.coli contamination gets any worse. According to Western Watersheds Project, the levels of E.coli in the Babocomari river right now are so high, they’re hazardous to human health upon contact with the skin.
“I think the BLM appears to be doing less to control trespass grazing than they have in past administrations,” said Tuell. “It looks worse. I was just out at the Babocomari. It was just cow pies the whole way, and cows aren’t supposed to be there at all. And I know that the Arizona Department of Environmental Quality knows this water is impaired for E.coli.”
Can cows help the environment?
The local ranchers have defended grazing in the area, saying that cows have no different impact on the land than deer and that grazing can help prevent fires.
Dr. Ethan Orr from the University of Arizona’s Cooperative Extension said that their research has shown that grazing can be beneficial to ecosystems if it's managed properly. But he said that none of this research had been done in riparian areas like the SPRNCA.
The scientists who have spent decades studying the SPRNCA and the environmental advocates fighting to have cows removed from the area were quick to say that cattle have a much different impact than deer and that grazing has a much more complicated relationship with fire.
“I don’t think it takes a genius to look at a cow and look at a deer and understand the difference in the impact,” said Makings. “Deer are browsers for one thing, so they’re not going to sit there and eat as much grass as they can. They’re browsing for shrub components and they move around, they’re much more skittish.”
Dr. Stromberg said that you can’t make a direct comparison between cattle and deer because cattle are much larger than deer and graze in much larger numbers. She said the ecosystem can’t handle this many large hooved animals.
Cows do technically prevent fires, but the scientists and environmentalists said that the relationship between the two was more complicated than this. Makings called it a classic scare tactic coming from the ranchers.
“There’s this saying that grazing prevents blazing,” said Tuell. “Yes, it’s true if you remove vegetation, it can’t burn. The same is true of paving, if you paved the SPRNCA it would not burn. If you mowed it, it would not burn. But the land was designed to burn and then the cows came in and removed the grass, and then there was nothing to burn. And they left their poop behind, often with invasive species of grass seeds and now it burns hotter and faster.”
The scientists also pointed out that the ecosystem in the SPRNCA is fire adapted and needs to burn occasionally to be healthy.
One of the invasive species of grass that have taken over the ecosystem is buffelgrass. This particular species is notorious for burning hot and long, causing devastating wildfires.
Dr. Orr thinks that cattle could be useful in combating buffelgrass. He thinks that through proper management, one invasive species could be used to help control another.
