Recovering area in Coyote Springs where tortoises are moving into the burned areas.

The wide expanses of golden annual grasslands seen in many Arizona and Nevada desert landscapes today are unnatural — the result of massive swaths of invasive, non-native brome grasses. These invasive grasses greatly heighten wildfire risk and frequency, suppressing native plant growth, harming many native animal species, drastically converting habitat types, incurring unnecessary burden to wildfire managers, and posing potential threats to desert air quality and to tourist hotspots such as Red Rock Canyon outside of Las Vegas and Joshua Tree National Park. USGS ecologists are collaborating with resource managers in Nevada and Arizona to test invasive grass removal methods and reseeding strategies to encourage growth of native plants like Mormon tea and blackbrush. Research is ongoing to determine a proper regimen of invasive species suppression, native plant seeding, and management of soil-seed reserves that will aid in the recovery of burned desert landscapes to their original balance and beauty. USGS is also monitoring the movements of desert tortoises that live around the burned areas and finding that each year of vegetation recovery is encouraging tortoises to move farther into the burned areas.

Tamarisk in the American West

Tamarisk is a familiar invasive species across the American West, occupying hundreds of thousands of acres of river floodplains since the 1960s.  This shrub or small tree, which is also known as saltcedar, has successfully colonized a range of sites. It especially favors those sites that are inhospitable to dominant native streamside plants because of high salinity, low water availability, and altered streamflow regimes downstream of dams. Researchers debate the extent to which tamarisk invasion has had negative effects, but this invasive species can and does alter habitat quality for some wildlife, water use by floodplain vegetation, and the frequency and intensity of wildfires.

The gaging station has been removed, but the approximate position of the original camera can be established from the background mountains. The channel has shifted back to the left, eliminating the cottonwood trees present in 1964, but black willow is obvious in the foreground, cottonwood seedlings and mature trees appear throughout the view, and non-native tamarisk is adjacent to the river channel.

Tamarisk Control

Tamarisk is now declining in abundance in some parts of its range in the West because of the release and spread of a biological control agent, a defoliating beetle. This decline because of the beetle is presenting opportunities for scientific research that examines the response of ecosystems as an invasive species declines or is controlled. Important questions that USGS scientists are working to answer include:  How does water consumption along rivers change as tamarisk abundance and vigor are reduced?  What plants will replace tamarisk as it dies back, and are these desirable native species or undesirable weedy species? How are wildlife populations — such as birds — responding to changes in habitat associated with vegetation change?  How can land and water mangers best approach efforts to restore floodplain vegetation to achieve their objectives?

USGS invasive species science, such as this tamarisk research, provides critical information for society on the economic and ecological price of controlling invasive species. Across the West USGS researchers have been tracking the amount of water that floodplain vegetation is using, including tamarisk and other plants that replace it as it dies back.  Along the Virgin and Colorado rivers in Arizona, Nevada, and Utah, USGS scientists are monitoring changes to vegetation communities over time, and working with stakeholders to plan and prioritize restoration efforts. At various sites around the West, including the Dolores River in Colorado and Utah, USGS scientists are monitoring the response of wildlife populations to changes in vegetation associated with the reduction in tamarisk due to repeated defoliation by the leaf-eating beetles.

Buffelgrass in the Sonoran Desert

African buffelgrass is spreading rapidly in the Sonoran Desert of southern Arizona, creating novel fire risks in both natural and urban areas and threatening conservation efforts. Left unchecked, buffelgrass will dominate the desert landscape and could cause regular, fast-moving wildfires that can burn neighborhoods, ruin viewscapes, close popular attractions, and even interrupt essential services. Urban areas that are expanding most rapidly now have to plan growth, development, and protection of public safety around a fast-evolving fire risk. The growing fire risk and environmental damage can harm tourism, decrease property values, and make it harder to attract good employers and retain high-skilled workers. Buffelgrass invasion also jeopardizes ecosystem health, ecological goods and services, and conservation measures, including protection of threatened and endangered species.

The most effective way to reverse the buffelgrass invasion and lessen its impacts is to tackle high-risk and high-value areas first, and pool resources to save costs and maximize control efforts across mixed jurisdictions. The Southern Arizona Buffelgrass Coordination Center, an NGO established in 2008, is raising awareness, quantifying risk, engaging policy and decision makers, enhancing capacity, and helping to build the technical knowledge to guide the control effort.

A Buffelgrass Decision-Support Model

Two ranging poles were placed near the positions of two sets of saguaros in order to determine their heights, and hence approximate ages. Most were established in the 1890s, after livestock grazing and the removal of fine fuels had begun in the area. Several small saguaros have become established since the fire; one is to the left of the left-hand ranging pole, another is hidden behind the blue paloverde at the center. Buffelgrass, an invasive nonnative grass, is abundant at this site and surrounds the desert hackberry) in the foreground.

A decision-support model that simulates buffelgrass spread and treatment effectiveness was developed by the Southern Arizona Buffelgrass Coordination Center, ESSA Technologies, and the USGS Invasive Species Program. This model’s prototype was developed for the Santa Catalina Mountains, Coronado National Forest, which borders the City of Tucson to the north. Important features of the model, including historical rates of buffelgrass spread and the density of buffelgrass at which biodiversity declines irreversibly (43 percent), were gleaned from plot studies in the target area.

The model was extended to Ironwood Forest National Monument, west of Tucson, with participation and funding from the Bureau of Land Management.  As a training exercise for how management decisions can be made using the decision-support model, a suite of management scenarios from area land managers were simulated and presented to public agency administrators who allocate funds and resources for buffelgrass control. The model and its adoption by multiple jurisdictions to manage buffelgrass at the landscape scale could serve as a template for routine cooperation in landscape conservation in Arizona and the Southwest.

To learn more about these and other species please visit the USGS Ecosystems Invasive Species Program website

Southern Arizona Buffelgrass Coordination Center

Tamarisk control, water salvage, and wildlife habitat restoration along rivers in the western United States

Salt cedar press release

This large Burmese python, weighing 162 pounds and more than 15 feet long at the time of its capture in 2009, was caught alive in the Everglades and was found to have eaten an American alligator that measured about 6 feet in length. University of Florida researchers in the photo: Michael Rochford is holding the python's head, and Alex Wolf and Therese Walters are holding the python's body.

Under Siege! America’s Most Unwanted Invasive Species

The United States is under an economic and ecological siege by alien invaders — America’s Most Unwanted. More than 6,500 of these harmful non-native species cause more than 100 billion dollars in damage each year to the U.S. economy as the country battles to control the economic, ecological, and health threats these invaders pose. Increased global travel and trade are providing more pathways for both intentional and unintentional introductions of invasive species.

Invasive species affect just about everyone in every State in the country, in urban centers and wilderness areas. And their costs are borne by all of us — farmers, ranchers, businesses, and local, State, Tribal, and Federal governments.

The Cost of Invasives

Costly effects of invasives include crop decimation (cactus and gypsy moths), clogging of water facilities (quagga and zebra mussels) and waterways (hydrilla, giant salvinia), wildlife and human disease transmission (West Nile virus, monkeypox, and diseases in some ships’ ballast water), threats to commercial, native, and farmed fisheries (Asian carp, snakehead fish, sea lamprey, Asian swamp eel, whirling disease, and viral hemorrhagic septicemia), increased fire vulnerability (cheatgrass, brome, and buffelgrass) and adverse effects for ranchers and farmers (leafy spurge and cheatgrass).

Researchers with the USGS Invasive Species Program work on every one of those species mentioned; in fact, our researchers work collaboratively on all significant groups of invasive organisms in terrestrial and aquatic ecosystems in all regions of the United States. Across the Nation, our invasive species experts partner with States, other Federal agencies, businesses, agriculture, and natural resource managers to help solve the problems posed by these invaders.

Key components of invasive species activities include prevention, monitoring and forecasting threats, and control and management of established invaders.

During Invasive Species Awareness Week, we will feature some of America’s Most Unwanted each day to highlight the impacts of invasive species to the nation’s Ecosystems and economy.

Burmese pythons are now found across more than a thousand square miles of southern Florida, including all of Everglades National Park and areas to the north such as Big Cypress National Preserve. This snake threatens both the native animals and ecosystems in South Florida because they eat a wide variety of prey (mammals, birds, and alligators), and pose a risk to the ecosystems and the animals that live in them, including many including threatened and endangered species. Scientists do not know exactly how many Burmese pythons are living in Everglades National Park, but they believe at least tens of thousands are there.

USGS Research on Burmese Pythons

Recent USGS research provides initial evidence that pythons may be able to survive in marine and estuarine environments such as bays, inlets and open seas. This study showed that in the lab, hatchling Burmese pythons were able to withstand exposure to saltwater long enough to indicate that the species could potentially expand its range through ocean and estuarine environments. These results raise concerns that the constrictor may invade nearby islands, such as the Florida Keys.

Other recent USGS and partner research has demonstrated that some mammal species have declined  in areas where Burmese pythons are established in Everglades National Park. For example the most severe declines, including a nearly complete disappearance of raccoons, rabbits, and opossums, have occurred in the remote southernmost regions of the park, where pythons have been established the longest. In this area, observations of raccoons dropped 99.3 percent, opossums 98.9 percent, and bobcats 87.5 percent. Marsh and cottontail rabbits, as well as foxes, were not seen at all. These mammal species were common in the park before pythons attained high densities, but research shows that their numbers have dropped dramatically over the same time that the pythons were becoming more abundant.

Fishing guide Camp Walker, Catalyst Charters, of Islamorada, Fla., took this photo of a Burmese python swimming in Florida Bay from the end of Twisty Channel toward End Key on Nov. 16, 2011.

Ongoing research may provide new tools that could limit python population numbers and help prevent further spread. In the meantime, agencies such as the USGS, National Park Service, Florida Fish and Wildlife Conservation Commission, and others are actively testing and applying control and eradication techniques, including trap development, refinement of visual searching methods, and testing detector dogs for locating pythons.

Brown Treesnakes

The invasive brown treesnake on the Pacific island of Guam is the poster child of the ecological and economic havoc an invasive species can cause. There, since the snake first invaded the island sometime right after World War II, mass extinctions of most of the island’s native birds, mammals, and lizards have occurred, which, in turn, have caused cascading and irreversible ecosystem changes.

For example, the loss of these native vertebrates means they are not available to disperse the seeds that pollinate trees and flowers. Consequently, some of the island’s native trees have greatly declined in abundance and may disappear. Similarly, as fish-eating birds have been lost from Guam by being eaten by the snakes, the natural nitrogen transport from aquatic and marine systems to bird rookeries has been lost as well, adversely affecting the growth of nitrogen-dependent plants on the island.

The Role of an Invasive

“Many invasive species take over the role previously occupied by a native species,” said USGS invasive snake expert Gordon Rodda, a scientist with the USGS Fort Collins Science Center. “While the non-native species might displace that native species, it doesn’t necessarily disrupt ecosystem processes. But when the brown treesnake came to Guam, it occupied a new role as a novel, arboreal night-time predator on birds, lizards, and mammals, a role to which these animals were not adapted.”

The result, said Rodda, is that with the extinction of most of the island’s vertebrates, the original ecosystem is simply not recoverable. It’s a cautionary tale for Florida where Burmese python populations are exploding.

Since Guam is overrun with brown treesnakes — as many as 13,000 per square mile in some places — current efforts focus on preventing them from invading the U.S. mainland or other snake-free islands such as the Northern Mariana Islands, Micronesia, and the Hawaiian Islands. This is challenging because shipping and air traffic from Guam to these other islands is a daily affair and because these snakes are masters at hiding in confined places where they can live a long time without food or water.

Prevention in Paramount

“Prevention of spread is paramount,” said Rodda. “It is much cheaper than intervention once a snake population establishes. With prey species that are unused to being hunted by snakes, invading brown treesnakes can remain well-fed with little effort while they continue to multiply. So it is crucial to keep alien species from sensitive environments.”

Without rigorous prevention, said Rodda, it is extremely difficult to control, let alone remove, an introduced reptile species. In the case of the brown treesnake, prevention efforts include working to detect stowaway snakes before they leave the island, as well as extreme vigilance on islands where the snakes are most likely to invade.

A multi-agency Rapid Response Team led by the USGS assists in detecting and capturing brown treesnakes that are found as stowaways or on other Pacific islands after being accidentally transported from Guam. This response team uses USGS research to help them improve their chances of finding snakes, as well as predicting the movements of snakes that could have accidentally made it to another island.

“If the brown treesnake gets to any of these other snake-free islands, it will find a veritable banquet of prey animals — and the same thing could happen there as happened on Guam,” Rodda noted. “It’s essential to get ahead of the curve and implement prevention efforts at the get-go, before an alien species becomes a problem.”

Of Parasites and Brown Treesnakes

As a consequence of being introduced to Guam in the late 1940s, brown treesnakes have been purged of the parasites that typically infect them in their native range, and which likely help keep their population numbers at reasonable levels. This freedom from natural parasitic enemies may help explain at least some of the ecological success of brown treesnakes on Guam.

Researchers at the USGS Western Ecological Research Center along with collaborators in Papua New Guinea, are investigating ways to exploit the natural parasitic and disease enemies of the snake as possible additional management tools for controlling the population on Guam, if not eradicating them altogether. Although much work remains to be done before experimental studies can begin on biocontrol efficacy, the findings of the USGS researchers to date are encouraging, and more exploratory work is on the horizon.

Eradicating this snake on Guam would have tremendous ecosystem, human health, and economic benefits, and would reduce the risk of invasion for other islands and the U.S. mainland.

Stalking Snakes:

Days (and Nights) in the Life of a Brown Treesnake Rapid Responder (contains a cool find-the-snake page to demo how difficult it is to see them!)

The Brown Treesnake on Guam

Brown Treesnake FAQs

Snakes in the Wrong Places: Gordon Rodda’s Career in Invasive Species Research