Invasive grasses are fueling wildfires across the US



Burning invasive, nonnative grasses on federal land at Lower Table Rock, Oregon.
BLM, CC BY

Emily Fusco, University of Massachusetts Amherst

The Santa Ana winds that help drive fall and winter wildfires in California have died down, providing welcome relief for residents. But other ecological factors contribute to fires in ways that scientists are still discovering.

I study how human actions affect fire regimes – the patterns through which fires occur in a particular place over a specific time period. People alter these patterns by adding ignition sources, such as campfires or sparking power lines; suppressing fires when they develop; and introducing nonnative invasive plants.

My research suggests that nonnative invasive grasses may be fueling wildfires across the United States. Some fires are occurring in areas that rarely burn, like the Sonoran Desert and the semiarid shrublands of the Great Basin, which covers most of Nevada and parts of five surrounding states. In the coming months, some of the grasses that help feed these blazes will germinate, producing tinder for future fires.

The Great Basin.
KMusser/Wikipedia, CC BY-SA

In a recent study, I worked with colleagues at the University of Massachusetts and the University of Colorado to investigate how 12 nonnative invasive grass species may be affecting regional fire regimes across the U.S. We found that eight species could be increasing fire in ecosystems across the country.

Altering historical fire patterns

A fire regime is a way to describe fire over space and time or to characterize fire patterns. Understanding fire regimes can help make clear that fire is a natural and integral component of many ecosystems. Knowing historical fire patterns also enables scientists to begin to understand when new or different patterns emerge.

The link between invasive grass and fire is well established. Invasive grasses are novel fuels that can act as kindling in an ecosystem where readily flammable material might not otherwise be present. They can catch a spark that might otherwise have been inconsequential.

For example, in August 2019 the Mercer Fire burned 25 acres in Arizona, scorching native desert plants, including iconic saguaro cacti. A much larger event, the 435,000-acre Martin Fire, destroyed native sagebrush ecosystems in Nevada in July 2018. Invasive grasses helped fuel both fires.

Cheatgrass, which fueled the Martin Fire, is a well-studied invasive grass known to promote fire. But many other invasive grass species have similar potential, and their roles in promoting fire have not been assessed at large scales.

How land managers are fighting invasive grasses across the Great Basin region of the West.

Introducing the suspects

Researchers describe fire regimes in many ways. Our study focused on fire occurrence (whether or not fire occurred), frequency (how many times fires occurred) and size (the largest fire associated with a place) in 29 ecological regions across the U.S. For each location we tested whether invasive grasses were associated with differences in fire occurrence, frequency or size.

A nonnative invasive species typically comes from another continent, has become established, is spreading and has negative impacts. We used an online Invasive Plant Atlas of the United States as a starting point to determine which invasive grass species to investigate.

Next, we searched the scientific literature and the U.S. Forest Service’s Fire Effects Information System to see whether there was reason to believe that any of the invasive grass species promoted fire. This process helped narrow our scope from 176 species to 12 that were suitable for our analysis.

Who are these “dirty dozen,” and how did they get here? Buffelgrass is native to Africa and was intentionally introduced to Arizona in the 1930s, probably for erosion control and forage. Japanese stiltgrass and cogongrass are native to much of Asia and were introduced to the southeastern U.S. in the early 1900s, in some instances as packing material. Medusahead, which comes from Eurasia, was introduced to the western U.S. in the late 1800s, probably by accident as a contaminant in seed shipments.

The remaining eight species – giant reed, common reed, silk reed, red brome, cheatgrass, Chinese silvergrass, Arabian schismus and common Mediterranean grass – have similar stories. People introduced them, sometimes accidentally and at other times intentionally, without an understanding of how they could impact their new settings.

Cogongrass, which is invasive in the U.S. Southeast, may burn hot enough to kill native fire-adapted tree species.
Alabama Cooperative Extension System, CC BY-ND

Big data for big questions

Understanding how multiple species influence fire over many years at a national scale requires using big data. One person could not collect information on this scale working alone.

We relied on composite data sets that provided thousands of records of invasive grass occurrence and abundance across the country. Combining these records with agency and satellite fire records helped us determine whether fire occurrence, frequency or size were different in places with and without grass invasions.

We also used statistical models to assess whether human activities and ecological features could be driving observed differences between invaded and uninvaded areas. For example, it was possible that grass invasions were happening near roads, which are also linked with fire ignitions. By including roads with grass invasion in our statistical models, we can be more confident in the role invasive grasses could play in altering fire regimes.

Our results show that eight of the species we studied are associated with increases in fire occurrence. Six of these species are also linked to increases in fire frequency. Invasions seem to be affecting a variety of ecosystems, ranging from buffelgrass in the Sonoran Desert to Japanese stiltgrass in eastern U.S. forests to cogongrass in southeastern pine systems.

Our statistical models suggest that grass invasion, along with human activities, are likely affecting fire patterns in these ecosystems.

Surprisingly, none of the invasive grass species analyzed appeared to influence fire size. We interpret this result to mean that the areas we studied are seeing more of the same types of fires that already occur there, at least in terms of size.

Dispersing seeds over a burned area of the 2015 Soda Fire in southwest Idaho to help stabilize soils and combat invasive weeds such as cheatgrass.
BLM via AP

Factoring invasive grasses into fire planning

People start an estimated 84% of wildfires in the U.S., with the rest ignited by lightning strikes. Studies show that climate change is increasing wildfire activity.

With an understanding of interactions between invasive grasses and fire, agencies that handle either fire or invasive species may find opportunities to work together to control invasions that can lead to more frequent burns. Our research can also strengthen predictions of future fire risk by incorporating the presence of invasive grasses into fire risk models.

Although it sometimes may feel as though the world is on fire, this information can provide potential for remediation, and may help communities prepare more effectively for future wildfires.

[ Like what you’ve read? Want more? Sign up for The Conversation’s daily newsletter. ]The Conversation

Emily Fusco, Postdoctoral Researcher, University of Massachusetts Amherst

This article is republished from The Conversation under a Creative Commons license. Read the original article.

What are native grasslands, and why do they matter?



The Southern Tablelands contain rare native grasslands.
Tim J Keegan/Flickr, CC BY-SA

Mike Letnic, UNSW

Coalition minister Angus Taylor is under scrutiny for possibly intervening in the clearing of grasslands in the southern highlands of New South Wales. Leaving aside the political dimensions, it’s worth asking: why do these grasslands matter?




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The grasslands in much of eastern Australia are the result of forests and woodlands cleared to “improve” the landscape (from a grazier’s point of view) to make it suitable for grazing livestock.

The “improvment” typically entails cutting trees, burning the felled timber and uprooting tree stumps, followed by ploughing, fertilising and sowing introduced grasses that are more palatable to livestock than many native grasses.

However, largely treeless native grasslands once occurred at high elevations across much of the Monaro tableland, in the area stretching between Canberra and Bombala.

The Monaro grasslands (or in scientific speak, the natural temperate grassland of the Southern Tablelands) are in relatively dry and cold areas, particularly in upland valleys or frost hollows where cold air descends at night.

The combination of dry climate and cold restricts tree growth and instead has encouraged grasses and herbs. Native grasses such as kangaroo grass and poa tussock dominate the grasslands, but there are many other unique plants. A typical undisturbed grassland area will support 10-20 species of native grasses and 40 or more non-grass species.




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When tree planting actually damages ecosystems


The grassy plains are also home to unique cold-adapted reptiles such as the grass-land earless dragon, little whip snake, pink-tailed worm lizard and striped legless lizards. This combination of plants and animals create a unique ecological community.

Striped legless lizards may resemble a snake, but most of its body is actually tail. It has vestigial limbs and a non-forked tongue.
Benjamint444/Wikipedia, CC BY-NC-SA

A fraction remain

It is estimated only 0.5% of the area that would once have been natural temperate grasslands in the Southern Tablelands remains. The rest has been gradually “improved” since the mid-nineteenth century to make them more productive for livestock grazing.

Livestock dramatically change the composition of grasslands, as animals remove palatable plants and compact the soil under their weight. Disturbed soil and the livestock also help to spread non-native weeds.

However, most native grasslands have not just been modified by grazing but completely replaced by man-made pastures. That is, the land has been ploughed, fertilised and the seeds of introduced grasses have been planted.




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Australia’s plantation boom has gone bust, so let’s make them carbon farms


These changes to the landscape mean much of the landscape is dominated by introduced plants and is now unsuitable for many of the native plants and animals that once lived and grew there.

Because the Natural Temperate Grassland of the Southern Tablelands is now so rare it is classified as critically endangered and federally protected. Furthermore, many of the distinct plants and animals that still live in these grasslands are classified as vulnerable or endangered.

The pink-tailed worm lizard is one of the rare species living in the native grasslands of the Southern Tablelands.
Matt Clancy/Wikimedia Commons, CC BY-SA

Some of the best remaining examples of the Monaro grasslands can be found in old cemeteries and in areas set aside as public livestock grazing areas. These areas of public land have often been spared from pasture improvement or only lightly grazed, and thus now support relatively intact native grassland ecosystems.




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While, to the untrained eye the Monaro grasslands may seem unremarkable and difficult to distinguish from grazing pastures, they are deeply important. They show us what Australia once looked like, and act as a haven for native biodiversity.

Indeed, what remains of the natural grasslands is now so disturbed by agriculture there is a real threat this distinctive ecological community and many of the species it contains may disappear altogether, if they are not protected from excessive grazing, fertilisers and the plough.The Conversation

Mike Letnic, Professor, Centre for Ecosystem Science, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.