Early one morning last summer, a spark landed in some dry grass near Lahaina in Maui. At first, residents were not alarmed. Fires have become common in Hawaii in recent years, but fighters generally contain them before they threaten residential areas. In 2020, the Ka’anapali fire had consumed 21 houses before being put out. But this blaze last August was different. Conditions were dry, and heavy winds pushed flames into residential areas faster than officials could issue evacuation orders. At least 2,200 buildings were destroyed, most of them residential homes. Over 100 people died.

Three days after the blaze, Governor Josh Green told CNN that the fire was likely driven by a combination of drought, global warming, and adverse weather conditions. Green may have been trying to deflect blame by identifying causes that are well outside the control of Hawaii’s government. But there was another key factor he didn’t mention: invasive grasses such as fountain grass (Cenchrus setaceus), Guinea grass (Megathyrsus maximus), and buffelgrass (Pennisetum ciliare). These plants are fire-adapted: they burn hot and fast, and they thrive after fires. According to the Hawaii Invasive Species Council, these grasses were imported mainly to provide forage for cattle. On ranch lands, cows keep these grasses in check. But invasive grasses will inevitably spread. Lahaina is surrounded by abandoned farm land: the state’s last pineapple and sugar cane plantations closed in 2009 and 2016, respectively. Nobody was controlling invasive grasses on these lands. That meant that nobody was controlling Lahaina’s fire risk, either.

The cruel irony of last summer’s deadly fire is that it could have been prevented. For years, experts had been sounding the alarm about the fire risk posed by invasive grasses. After the almost-deadly Ka’anapali fire, Maui County produced a report on wildfire prevention. It identified non-native grasses as a key fuel and recommended that the county implement an “aggressive plan” to replace invasives with native plants on public lands, and engage collaboratively with private landowners. But little was actually done to implement the recommendations.

Hawaii is not alone. I live in Arizona’s Sonoran Desert, which, as in Hawaii, has been invaded by buffelgrass and other fire-adapted non-native weeds. And also as in Hawaii, experts here have been warning us for years that these invasive grasses are increasing our fire risk. But it’s not just increased fire risk that has us worried. After a blaze, buffelgrass will re-grow, but our native cactus, trees, and shrubs will be gone forever. We face the risk of wholesale ecological state change. My colleague Julio Betancourt, a retired U.S. Geological Survey scientist, uses the term grassification to describe the rapid, terrifying conversion of our biodiverse and traditionally fireproof desert ecosystem into a fire-prone grassland. A large and growing body of research documents that buffelgrass is transforming our desert and its fire regimes, pushing us into uncharted territory. The Tucson area is full of neighborhoods that abut dense patches of buffelgrass. A stray spark on a windy day could bring Lahaina’s tragedy, or something close, to my home in the desert.

And invasive species do more than just change our fire regimes. Last month, the Intergovernmental Science Policy Platform on Biodiversity and Ecosystem Services issued the first-ever comprehensive assessment of the state of the science on invasive species, their costs, and management strategies. The IPBES report concluded that invasives undermine biodiversity: biological invasions were a driver in 60 percent of known species extinctions, and the sole cause of 16 percent.

Biological invasions also destroy crops, clog pipes in power-generation and water-treatment facilities, and threaten critical endangered species habitats. These costs add up. The IPBES estimates that globally, invasive species cause some $400 billion worth of damage annually. Turning to the U.S. ecology, a recent study published in Science of the Total Environment estimates that biological invasions cost the United States at least $1.22 trillion between 1960 and 2020, primarily in damages to agricultural productivity and terrestrial habitat. Even more alarming, these costs have increased exponentially, from around $2 billion annually in the 1960s to $21 billion in 2020—a figure that the study authors themselves acknowledge is severely underestimated because they didn’t use unreliable data. We face a future where invasive species will cost us more and more, unless we figure out how to manage them.

For the past five years, I’ve been studying the way we manage buffelgrass in our area, and thinking about what that tells us about effective policies and programs for invasive species governance. Here in Arizona, the experts’ warnings have not fallen on deaf ears. Our county has programs to educate citizens about buffelgrass; local conservation groups and land managers have formed a Cooperative Weed Management Area to coordinate removal efforts; and the state recently increased funding for invasive species removal. But these efforts take time, and buffelgrass is spreading faster than we can act. Our existing policies, programs, and funding mechanisms are not enough to protect citizens here from the kind of tragedy that occurred in Lahaina.

Governance is always complex in the federalist system, but for most policy areas, we have a clear idea about how authority and responsibility are allocated across multiple levels of governance, and whom to hold accountable when things go wrong. However, unlike in other areas, it’s not always clear who has—or should have—authority and responsibility to address invasive species. When it comes to air and water pollution, there are clear roles for both federal and state government. When it comes to wildlife, states have general authority and responsibility to manage wild animals, subject to federal authority over endangered species and public lands. But authority and responsibility for biological invasions is murkier. We have no single comprehensive federal policy on invasive species management. There is a National Invasive Species Council staffed by the Department of the Interior that conducts research and helps to coordinate management activities across federal agencies. The Forest Service, the Bureau of Land Management, and the Park Service provide guidance to local land managers within their agencies’ domains. The Park Service maintains 15 regional Invasive Plant Management Teams that can be dispatched to tackle problems within the national parks. When Congress is feeling generous, lawmakers sometimes provide funding for local research and mitigation efforts. Many states have their own programs to identify and manage biological invasions within their boundaries. Localities can establish their own Cooperative Weed Management Areas, called CWMAs, or Cooperative Invasive Species Management Areas, called CISMAs, to coordinate local efforts.

The end result is that many, many different governmental agencies and nonprofit organizations are exercising authority to manage invasive species, sometimes quite effectively. But authority and responsibility are two different things. It’s not clear that anyone has assumed the responsibility to prevent tragedies like the wildfire in Lahaina, or the more common, less tragic, but still costly problems that occur when invasions chip away at our ecosystems and infrastructure.

It’s tempting to think of biological invasions as a technical problem, and focus our policy efforts on developing and disseminating technical solutions, like biological controls or herbicide treatments. Here in the Sonoran Desert, a lot of the early buffelgrass effort was focused on developing technical solutions. It took a few years and some experimental research, but we now know how to get rid of the stuff, although it’s not quick or cheap or easy to do. You can either pull plants by hand, or you can spray glyphosate twice a year, timing your spraying for just after the rainy season, when the grass greens up. Either way, you have to repeat the process annually for five years until the seed bank has lost its potency. And either way, if you want to reach a big patch that’s deep in the desert, you need either a helicopter or a crew of very fit people.

But technical solutions only work if they are implemented. Here in Arizona, buffelgrass has invaded a complex patchwork of publicly and privately managed lands. In Pima County alone, we have a national park, a national forest, county conservation land, the Tohono O’Odham tribal nation, ranches, ecotourism resorts, and numerous real estate developments. That’s a diverse group of land managers. To keep buffelgrass in check, we need cooperation across all these actors. But not everyone has the same motivation, information, or resources to manage buffelgrass on their lands. Our public land managers have the motivation and know-how, but often have insufficient money or personnel to treat their lands fully. Private land managers tend to have the resources, but may lack the motivation and information to take appropriate action. Our local CWMA works hard to bring these land managers together, but participation is voluntary, and not all land managers attend regularly. It’s telling that in Lahaina, fires were incubated in abandoned farmland. Invasive grasses thrive in places with absentee or inattentive landowners.

When I first started considering policies that might be effective for addressing invasive species, I immediately thought of regulatory solutions. In Idaho, where the CWMA concept was first pioneered to address invasive aquatic plants, regulators have the authority to inspect private property for listed invasive species. If the species is detected, regulators can ask the property owners to address the problem, or alternatively, remove the species themselves and bill the landowner. This seemed like a promising solution, so I wondered why it hadn’t been applied to buffelgrass. It turns out that Pima County has a similar law on the books, but it’s never been used. The county itself is a landowner with major infestations, and county officials felt it would be hypocritical to regulate private lands when they couldn’t comply with their own regulations. To be fair, the county has been both active and pro-active on buffelgrass, eradicating it from ecologically and recreationally important parcels of county land and developing education programs. But Pima County lacks the resources to cope with buffelgrass on all of the land it owns and manages. The regulatory “solution” was not going to solve this problem.

In my environmental policy classes, I teach students about the Cuyahoga River, and how its habit of catching on fire throughout the 1960s helped motivate passage of the Clean Water Act. Back then, we had no models for how to regulate industrial pollution, and from a constitutional perspective, it wasn’t really clear that this was an area where the federal government had any authority at all. I often wonder what it must have been like to be a senator from Ohio, seeing the Cuyahoga catch on fire, knowing that pollution had become an unacceptable burden on society, but having no mental model for addressing the problem. We eventually settled on a model with pollution as a negative externality generated by industrial firms. Congress gave EPA authority to create a permit program that limits these businesses’ ability to use our nation’s rivers as a cheap waste-disposal system. The CWA isn’t perfect, but our water is a lot cleaner, and we now use this kind of regulatory model to address a wide range of pollutants.

I propose that we start thinking of invasive species as a common bad. Common bads differ from environmental externalities because they are co-produced by multiple, diffuse sources, making them hard to regulate. Many readers will already be familiar with the difference between point-source and nonpoint-source pollution. Point-source pollution comes from firms’ smokestacks and discharge pipes, making it easy to understand the problem as an externality, and making it easy to identify and regulate polluters. Nonpoint pollution, on the other hand, is jointly produced by a lot of different actors. Nonpoint pollution washes into the water when it rains, and is affected by the collective decisions that people in the watershed have made about how land should be used and managed, how farmers plant and fertilize their fields, and what kind of stormwater infrastructure there is in the area.

EPA addresses nonpoint pollution, but not through the regulatory approach used to control point-source pollution. Instead, the idea is to work with state and local officials to identify locally appropriate best management practices to reduce nonpoint pollution, and then use funding and incentives to encourage people to adopt those practices. There’s no particular punishment for actors that decline to adopt BMPs, but states have a general responsibility to collect data on water quality and share it with EPA. In watersheds where nonpoint pollution is particularly acute, federal and state programs may not be enough to improve water quality. In those places, local collaborative groups often emerge who bring together government, industry, civil society, and citizens to work together to understand, address, and monitor watershed quality.

We can think of invasive species as a common bad because—as is nonpoint source pollution—invasives are jointly produced by multiple actors and activities. In Arizona, buffelgrass was first introduced in the mid-20th century as a form of erosion control on rangeland, needed to correct dustbowl-like conditions after years of overgrazing. For a few decades, it mostly stayed where it was planted. But buffelgrass plants produce a lot of seeds, and they can lie dormant in the landscape for years waiting until the conditions are right. The Sonoran Desert is patchy, with lots of bare ground between native plant clusters, and after a decent rain, buffelgrass seeds will sprout in those bare patches.

We stopped planting buffelgrass purposefully years ago, and even ranchers in our area find it makes for poor fodder. But folks in our community often provide unwitting assistance. People spread buffelgrass seeds when they drive or hike in the desert. When developers and road-builders disturb desert soil, they create conditions for buffelgrass to thrive, especially if they neglect to re-establish native plants after construction is finished. In Tucson, buffelgrass seeds spread throughout the dry streambed washes that drain the city during our summer monsoon season. Our research team recently did an urban buffelgrass survey, and found that the plants cluster most in places that aren’t actively managed: in alleys, on abandoned properties, in cracks at the base of streetlights. Like nonpoint source pollution, reducing the presence of buffelgrass requires different types of people to change the way they use and mange land and infrastructure.

But invasive plants can have features that present additional challenges. Buffelgrass is contagious, capable of colonizing new locations as long as conditions are suitable. As a result, biological invasions have a temporal element: an early stage when the invader is first introduced to a landscape, either intentionally or inadvertently; a mid-stage when it becomes established on the landscape; and a late stage when it expands or spreads.

Invasions can also have tipping points that, once reached, are ecological points of no return. In Arizona, it took decades for buffelgrass to become well-established on the landscape. It wasn’t until the 1990s that conservationists realized that it was a problem, and by then we had reached a tipping point: our public lands were infested with thick buffelgrass patches, and eradication was not going to be an option. Instead of removing buffelgrass from the landscape, we have to think about managing it to avoid tipping points such as catastrophic fires or a permanent ecological state change from desert to grassland.

There is a cruel irony here. It’s easier and more cost-effective to eradicate alien species during the early stages of the invasion, but we often don’t recognize them as a problem or know how to remove them until they are more widely established. If it takes us a long time to identify the invader as a problem and then start mobilizing a response, it may be infeasible or cost-prohibitive to eradicate the invader entirely. Recognizing this, a number of jurisdictions now focus on early detection and rapid response, hoping to thwart the next contagion before it become established and prohibitively expensive to remove.

There is another cruel irony, more political in nature. Political scientists Andrew Healy and Neil Malhotra have shown that when it comes to natural disasters, voters are myopic: they reward incumbent politicians who deliver post-disaster relief funds, but are indifferent to those same incumbents’ efforts at pre-disaster preparedness. This gives political leaders an incentive to under-invest in disaster prevention efforts. Applying Healy and Malhotra’s findings to biological invasions, political leaders may be reluctant to fund efforts aimed at preventing harms from invasive species. Waiting to act until after harm has occurred may be good politics, but it’s bad conservation, and leaves ecosystems and human communities vulnerable.

If we really want to understand invasive species, then, we might think of it as a contagious common bad, one that is easier and more cost-effective to deal with before it’s well-established in the landscape. Invasive species are not the only contagious common bad; pandemics and mis-information also fall into this category of problem, and lessons learned from dealing with biological invasions may well apply to these other problems, too. How does this mental model help direct us toward more effective policy solutions?

For starters, thinking of biological invasions as a common bad confirms that much of the existing work to address invasives is headed in the right direction. Show me a place where an invasive species has been eradicated or kept well under control, and I will show you a place where a diverse group of local governmental and community actors is working together to address a common threat—an ecosystem, a beloved species, an agricultural crop that is endangered by a biological invasion. Idaho first pioneered the CWMA model when it realized that invasive aquatic plants didn’t respect jurisdictional boundaries; if public land managers wanted to protect the state’s rivers and streams from invasions, they would need to bring together federal and state land managers, local anglers and boaters, and community groups, and that they would all need to work together to develop and implement solutions.

The cooperative approach is headed in the right direction, but it would work better with more support. Our local Sonoran Desert CWMA employs two half-time staff members, which is a good start, but it’s really only enough person-power to sustain a few basic activities: regular meetings and outreach; a few annual events to spread awareness and recruit volunteers; a few annual initiatives to find new grants or educate a new crop of congressional representatives. Right now, the CWMA serves mainly as a coordinating body, helping individual participants to share information and coordinate their efforts. People who work on buffelgrass here have long had bigger ambitions: a coordinating center that could pool resources across all land managers, public and private, one that would enable us to attack the problem where it’s most prevalent rather than in the places with the most willing and able land managers. About 15 years ago, they even started such an organization, but it collapsed within a couple of years, unable to find funding to sustain its own existence, let alone pilot a new cooperative model for weed removal. Local cooperative efforts can be incredibly effective at addressing biological invasions, but take time and effort. We need more comprehensive funding mechanisms to help create and sustain these local cooperative efforts.

Second, our efforts on invasive species need to include processes for early detection and rapid response so that contagions can be contained at the start. Here, too, existing efforts are already headed in this direction. Several states have established early-detection and rapid-response teams, and in many regions the national parks use this strategy as well. As with the local cooperative model, early detection efforts are occurring but operate in an environment with limited funding. A 2022 white paper by the National Invasive Species Council explores how the federal government can help fund and support early detection efforts. The slowly emergent model is one in which states develop early detection and rapid response programs, with support—funding, resources, strike teams—from the federal government. But slowly emergent models aren’t enough to address the problem.

Third and finally, we need to do more than simply authorize state and federal action on invasive species. We need to designate responsibility for preventing harms from invasives, ideally to state officials who are in a good position to scan their local landscape for emerging invasions that can be contained, as well as for established invasions that threaten major disasters or tipping points. Assigning responsibility could help to address the problem of the myopic voter by making government agencies—rather than elected officials—responsible for preventing disasters or economic losses driven by invasive species. It can be hard to assign responsibility for common bads; they are complicated and messy, and outcomes are driven as much by history, chance, and weather as they are the efforts of any state agency. But it is reasonable to expect state officials to monitor risks from biological invasions, make plans to address those risks, and report back to the public about how those risks are changing over time.

Ironically, this is exactly what the state of Hawaii has begun to do. As an island state with a globally important and unique ecosystem, Hawaii has long been proactive on invasive species, but like Arizona, it is grappling with the legacy of an earlier era when people imported new plants without recognizing the long-term consequences. In 2017, the state’s land management agencies adopted Hawaii’s first Interagency Biosecurity Plan. Land management agencies have taken it upon themselves to accept responsibility for monitoring biosecurity threats, making plans to address those threats, and reporting to the public and the legislature their progress on mitigation. Much of the plan focuses on intercepting invaders at Hawaii’s borders, and identifying and addressing invasions before they can become well-established. But the plan also includes a number of activities that might have prevented the Lahaina fire: a comprehensive threat assessment; and outreach to private landowners. Unfortunately, the plan is relatively new, and the relevant agencies hadn’t yet completed all of the 150 action items it identified.

Other states, including Arizona, have yet to accept responsibility for assessing and addressing threats from invasive species. Congress provides useful funding for research, mitigation, and coordination, but these efforts are mostly ad-hoc and mostly focused on public lands. Contagious common bads require more systematic efforts. Congress should consider an approach that assigns states the responsibility to monitor, plan for, and report regularly on invasive species and the threat that they pose. Such an approach should also focus on increasing state and local actors’ capacity to identify invasions quickly and address them early, before plants are well-established and impossible to contain. In the meantime, we remain increasingly vulnerable to the disasters—humanitarian, economic, and ecological—that invasive species can cause.