Changing Times in the West
On the morning of July 5, 2018, I woke up in my tent in northern Nevada and emerged to see the northern horizon completely obscured by a dark cloud of smoke with an ominous plume resembling a nuclear mushroom cloud rising thousands of feet into the air. I was in Nevada conducting field research on fire ecology in sagebrush ecosystems with my mentor, and only a day after we arrived in the area, the Martin Fire started about 30 miles north of our camp. Over the next few days, it grew into the largest fire in the country this year, and one of the largest in U.S. history, scorching over 430,000 acres in less than a week and moving up to 15 miles an hour when winds were highest.
Figure 1: The nearly 450,000 acre Martin Fire projects a smoke plume high into the sky, N of Winnemucca, Nevada
Thankfully, no homes were destroyed nor people injured, due to the remote location of the ignition and favorable winds which pushed the fire away from most development. However, vast amounts of rangeland were destroyed, leaving local cattle ranchers with a questionable future, and a significant portion of habitat for the vulnerable sage grouse was lost to the blaze.
In the midst of a Western population boom and with the effects of climate change becoming increasingly evident each year, wildfire has more than ever before become a tangible threat in the Western U.S. Natives to the region and transplants alike are feeling the heat from California to Colorado as the length of wildfire season and the amount of abnormally large and intense fires continue to trend upwards throughout the Western states.
As these tragic events continue to unfold, some have been quick to attribute the devastating wildfires to singular causes such as climate change or inadequate forest management practices. More and more, the causes of wildfire have become a political issue, with those in charge choosing to blame wildfire on singular causes and ignoring the nuanced reality of wildfire science. In breaking down the causes of wildfire in the West, it is essential to have an understanding of regional ecology and geography.
The natural pattern of fire occurrence for a particular ecosystem is called a fire regime. A natural fire regime is an ecological benefit. Occasional fire can clear dead material, release nutrients into the soil, and reduce competition for sunlight, all of which help vegetation thrive. However, ecosystems are very sensitive to changes to the natural fire regime which can lead to changes in species composition, loss of habitat, and even conversion into new ecosystem types.
One region which has experienced dramatic fire regime shifts is the Great Basin, which includes most of Nevada as well as parts of western Utah, southern Idaho, and southeastern Oregon. One of the largest fires driving fire regime changes in this area is the invasion of non-native cheatgrass, a fire prone grass which is wreaking havok on the Great Basin’s fragile sagebrush shrubland. While many different management strategies have been implemented to slow the advance of cheatgrass and help maintain a natural fire regime, none have been particularly successful. Recently, though, land managers are hopeful that a newly developed natural bacteria treatment can be used to curb the spread of cheatgrass, potentially creating a long term solution to a problem that has spanned decades.
The Great Basin: A Tale Of Changing Fire Ecology
The Great Basin region is a great example of the interaction between fire regime and ecosystem changes. This arid region covers over 200,000 square miles and includes the largest desert in the United States: the Great Basin Desert. This region is characterized by wide flat valleys (basins) that are separated by mountain ranges running in a common north-south direction and receives between 6 and 12 inches of precipitation a year. Due in part to the wide range of elevations in the region, a variety of ecosystems can be found here, ranging from subalpine forests in the highest ranges to alkali deserts in the lowest valleys. However, the most extensive ecosystem in the Great Basin is the sagebrush steppe, which fills most of the basins between mountain ranges. The Great Basin sagebrush steppe has been described in the past as an unbroken “sagebrush sea”, but since the 19th century introduction of the invasive annual grass Bromus tectorum, also known as cheatgrass, shrublands which used to appear endless have been diminishing and are rapidly being replaced with grassland.
Figure 2: Sagebrush steppe is the most extensive Great Basin ecosystem, but the “sagebrush sea” is under threat due to invasive cheatgrass.
The Cheatgrass Grass-Fire Cycle -- Disturbance & Resilience
The spread of cheatgrass throughout the Great Basin has led to drastic fire regime changes, and through this, extensive ecosystem shifts from sagebrush steppe to cheatgrass-dominated grassland. In order to understand what drives this conversion, it is useful to define a few concepts:
Disturbance refers to any discrete event which leads to changes in ecosystem species composition, available resources, or the physical environment. Fire is one example of an ecosystem disturbance, other examples are livestock grazing or even the construction of new infrastructure in an ecosystem.
Ecosystem resilience is defined as the ability of an ecosystem to recover to its natural state after a disturbance such as fire, grazing or disease.
Resistance is related to resilience but instead describes the ability of an ecosystem to retain its natural state in the presence of disturbance.
Using these terms, the sagebrush steppe of the Great Basin can be described with respect to its resilience to disturbances such as fire and its resistance to invasive species such as cheatgrass.
Cheatgrass Brings More Frequent Fire To The Great Basin
Additionally, it is important to understand the attributes that contribute to a region’s fire regime. One of the most important components of a regional fire regime is the fire return interval (FRI), which, defined simply, is the expected amount of time it would take for a location within the ecosystem to burn twice. Historically rare wildfire allowed sagebrush to grow in large, continuous stands separated by sparse native bunchgrasses prior to the introduction of cheatgrass to the region. Recent studies have estimated the sagebrush steppe FRI at somewhere between 50 and 150 years between burns. In contrast, the FRI of cheatgrass grasslands is estimated to be as low as 5 years depending on local conditions.
Other fire regime components include fire season length, average fire size, and fire intensity. All of these fire regime characteristics are changing in the Great Basin, but fire return interval is particularly important in understanding the ecosystem changes taking place here. This is because arid environments such as the Great Basin do not naturally burn frequently, and are thus very sensitive to changes in FRI. Sagebrush steppe has a relatively low resilience to burn disturbance events and can take decades to reestablish after a severe burn. This is contrasted by cheatgrass, which is adapted to thrive with frequent wildfire.
Figure 3: An extensive annual cheatgrass grassland area north of Winnemucca, NV. Cheatgrass grasslands have a much lower fire return interval than native sagebrush steppe, a characteristic that allows cheatgrass to dominate native species.
Cheatgrass and Fire: A Perfect Pair
There are several characteristics of cheatgrass that allow it to flourish in combination with wildfire in the Great Basin:
1. It grows earlier than native plants.
As an annual species, cheatgrass grows in thick stands during the spring of each year after the winter snowfall has begun to melt and then dries out and dies in the summer heat after releasing seeds for the next growing season. Because cheatgrass begins growing earlier in the year than native perennial grasses, it depletes available resources for later growing plants, giving cheat a competitive advantage, ecologically speaking.
2. It’s great at reproducing.
The mass die-off each June leads to an extensive seedbank stored in the soil which allows for successive generations to grow. Due to the large seedbanks stands of cheatgrass create, cheatgrass has a high resilience to disturbances such as fire. Contrastingly, native perennial grasses and sagebrush in the Great Basin do not produce comparable seedbanks, leading to low resistance to disturbance events.
3. It grows in dense, continuous patches, unlike native species.
As the summer progresses, dense stands of cheatgrass lose moisture content, forming a layer of bone-dry fuel perfect for wildfire ignition. Since cheatgrass typically grows in dense, continuous stands, this layer of dry material can connect patches between individual plants within sagebrush steppe, creating a continuous bed of fuel for wildfire and allowing an initial ignition to spread quickly into the surrounding shrubs. Native “bunch-grasses” have a much more sparse growth pattern, with bare ground separating individual plants which makes it harder for fire to spread.
Figure 4: A heavily invaded sagebrush steppe ecosystem at risk of more frequent wildfire brought by cheatgrass advance and subsequent fine fuel buildup
4. Cheatgrass capitalizes on fire events to dominate its competition
A fast, hot fire burning in dry cheatgrass in the summer clears litter and dead material and kills species that would compete with the cheatgrass during the following spring’s growing season. If a hot enough fire spreads into neighboring sagebrush steppe, it can blaze through both sagebrush and native grasses, leaving a clean slate for cheatgrass to spread into the following year, making an area even more fire-prone. This feedback pattern, called the grass-fire cycle, is common in many annual grasslands, but results in extreme disturbance for ecosystems such as sagebrush steppe which are simply not adapted for frequent burns.
Figure 5: A past burn east of Winnemucca, NV has eliminated sagebrush steppe which was easily replaced by dense cheatgrass in post-burn years.
This perilous introduction of a new fire regime type to the region has led to extensive loss and fragmentation of the once pristine sagebrush steppe found throughout the Great Basin.
Consequences of Changing Great Basin Fire Regimes
The Sage Grouse
Landscape scale ecosystem change such as that taking place in the Great Basin can have serious consequences for local residents, both human and animal. The greater sage grouse has made recent headlines for being at the forefront of land management debates throughout the sage-country. Sage grouse, known for males’ unique and sometimes comical mating rituals, have recently been listed as threatened by several international organizations, one short step below endangered status. In fact, their population is estimated to have declined by over 90% since their first discovery during the time of western expansion. The birds’ threatened status has led to them being central to the argument between conservationists, ranchers, and extractive industry leaders over how best to utilize and manage the vast amount of public land in the Great Basin region.
The main cause of the sage grouse’s dramatic decline stems from the fact that they are permanent residents of their breeding grounds in the sagebrush. Since the greater sage grouse does not migrate to breed, destruction of their protective sagebrush habitat leaves them with nowhere to raise their young. While industry and urban development have certainly contributed to the destruction of the sage grouse’s habitat, a vast amount of the habitat loss threatening sage grouse populations has been due to cheatgrass’ advance and the loss of sagebrush steppe to the grass fire cycle.
Figure 6: A male sage grouse beginning his mating rituals in the Great Basin. Photo: Bob Wick/BLM
Human Lives and Livelihoods
In addition to threatening species such as the sage grouse, the economic and human consequences of cheatgrass influenced wildfire are impossible to ignore. Federal fire suppression cost in 2017 was the most in history, with over $2.9 billion spent on fighting wildfires, compared to $800 million in 2010. In addition, 2015 and 2017 were the first years since modern records have been kept with over 10 million acres burned in the continental U.S.
Looking beyond the raw numbers of dollars spent and acres burned, wildfire threatens people, homes, and businesses, especially in more populated places. The dangerous consequences of fire in densely populated areas are exemplified by the catastrophic damage caused in California over the past several years; the year 2017 set records (which have successively been broken in 2018) for the most wildfire deaths and destroyed structures for the state, with total economic losses estimated at over $200 billion. While the Great Basin is less densely populated than California, as people continue to flock to the West, urban areas in the region are expected to grow dramatically. This would place more people and property in harm's way as wildfire activity is projected to continue to increase.
Can Bacteria Save the Sagebrush Sea?
What can be done to slow down the advances of cheatgrass and restore native fire regimes to this imperiled region? One innovative new method of cheatgrass management has been suggested by USDA Agricultural Research Service researcher Ann Kennedy. Back in 1986, Kennedy was tasked with finding ways to help wheat grow in Washington state, when she discovered a bacteria called Pseudomonas fluoresens which had peculiar effects on the soil and the plants that grow in it. The bacteria, which is a naturally occurring member of the microbial soil communities common in many Western regions, appeared to inhibit root growth for grasses and thus the number of shoots which could grow during growing season. Kennedy followed her hunch that she could be onto something big and proceeded to test over 25 thousand strains of Pseudomonas fluoresens and other bacteria found in local soils over the following three decades.
She found one strain in particular to be an extremely effective weed suppressor and dubbed it ACK55. After determining that ACK55 has no effect on native grasses and plants or wildlife, Kennedy submitted ACK55 for EPA registration as a natural herbicide specifically tailored to inhibiting cheatgrass growth. Incredibly, her research found that within 3 years of being applied, ACK55 had reduced cheatgrass cover by half, nearly eliminating it within five years.
Rangeland managers throughout the Great Basin are anxious to begin implementing ACK55 in their fight to maintain sagebrush steppe across the region. Since spraying the entire 200,000 square mile area would consume massive amounts of resources and time, two methods have been suggested to begin putting the bacteria to use:
The first strategy suggested is to coat native grass seeds with the bacteria, which does not affect their growth, and then to spread these seeds across burned areas after a wildfire. This would allow for the native perennial grasses to have their best chance to take root, as the competitive advantage cheatgrass gains through an early growth season would be all but eliminated, allowing more nutrients and water to be taken up by natives.
The second method of applying ACK55 involves directly spraying the soil surface, ideally targeting the forward edge of particularly invaded areas. By targeting these areas, the spread of cheatgrass into uninvaded sagebrush steppe could hopefully be slowed or even stopped. However, this would require a deep understanding of the spatial pattern of cheatgrass invasion and associated ecosystem conversion over time across the Great Basin, a task which for the most part has eluded researchers at a regional scale.
This is an application where I hope my current research project can be of use. I have been working on creating a time series dataset which maps cheatgrass grassland and sagebrush steppe across the entire Great Basin region annually over the past three decades. Once completed, it could provide the missing piece land managers need to find and target the most heavily invaded areas with ACK55.
For the first time in years, there is hope for a viable solution to cheatgrass and fire driven ecosystem loss in the Great Basin. Despite the long road Ann Kennedy has fought to get approval for ACK55 application, it appears to be on the verge of being adopted into the range management arsenal for Great Basin land managers. If it gets approval, it could mean positive things for the greater sage grouse, as well as the local residents who make their living in the Great Basin. If land management agencies can implement ACK55 quickly and efficiently, there still may be time to save the sagebrush sea.
To read more about my research using machine learning to understand cheatgrass and fire in the Great Basin, see my previous Earth Lab blog post: Understanding Fire Ecology Through Machine Learning.