Photo: Bon Accord Fire, Southwest Montana, 2020. © 2020 Delena Norris-Tull
Rangeland fires
Many forests are actually classified as types of rangeland, but for this section, I will use “rangeland” in the more common usage, in reference to the non-forested ecosystems of the Western States. Western rangelands include grasslands, prairies, sagebrush steppes, and deserts. Refer to the section “Rangeland Restoration” for details on some restoration projects within those ecosystems.
Native Americans have used controlled burns on rangelands for centuries before Anglo-Americans came onto the scene. In recent years rangeland fires have increased dramatically. These fires, occurring mainly in Western States, such as in the Great Basin and other areas, receive much less attention, both in the news media and in Federal agencies, due to the relatively low human populations in these areas. But there is a widening extent of the damages, especially to natural ecosystems, due to these fires.
Recent wildfire seasons have punctuated the critical need to reduce wildfires. In summer 2017, for example, a number of Western States, including Montana, exhausted their State funds to fight wildfires long before the fire season came to an end. And in warmer, southern states, such as California, the summer fire season extended well into late fall.
According to an article by Nick Bowlin, 2019, “Historically, sagebrush habitat burned about once every century or less, but now it happens every five to 10 years. Over the past two decades, more than 15 million acres of sagebrush have been permanently lost to wildfire.” Since 2000, more acreage has been lost to shrubland or grassland fires than to forest fires. Sagebrush habitat is host to about 350 species of native plants and wildlife. Greater sage grouse habitat has been reduced to near extinction levels. “The fires also harm watersheds, cause erosion, and destroy wildlife corridors used by pronghorn antelope, mule deer and elk.”
Many rural counties and many ranches suffer infrastructure damage and livestock losses from these fires. There are fewer Federal funds to assist with managing rangelands, in comparison to farmlands and forests. The BLM, which manages public rangelands, is severely underfunded, in comparison to the US Forest Service, even though the BLM manages 50 million more acres of public land than does the Forest Service.
What are the factors that are increasing the number and intensity of rangeland fires?
Climate change
Natural drought patterns are becoming exacerbated by global climate change. Recent high summer temperatures and drought, both exacerbated by climate change, have resulted in the hottest, driest summers, particularly in Western States, in recorded history. In the Western US, higher temperatures, combined with fire suppression policies, and the large increase in agricultural monocultures has allowed fires to become a greater problem every summer. All the climate-related problems described above are also creating problems in the non-forested regions of the West.
Invasive plants: Role in rangeland wildfires
Invasive plant species have the potential to alter various aspects of fire regimes, and thus can permanently alter ecosystems. As sagebrush ecosystems in the West have been decreased due to over-grazing, expansion of agriculture, and expansion of human populations, cheatgrass and other invasive plant species have expanded into the rangelands.
Cheatgrass, Bromus tectorum, long a popular forage, and an annual, non-native grass, is now being viewed as an invasive species in many areas of the West. Because it is still used as forage, it is not included on most State lists of noxious weeds, and it is not included on the Federal list of invasive species. However, several Western States (California, Colorado, Montana, New Mexico) have now included it as a noxious weed that is widespread and needs to be monitored and researched, to limit its spread. And a few Counties in Western States have added it to the County noxious weed list. Controlling its spread to reduce rangeland wildfires is becoming a priority in Western States.
Brooks, et al., 2004, state that the spread of cheatgrass across Western States has increased the frequency of rangeland fires “to the point that native shrub-steppe species cannot recover.” In sagebrush steppe habitats, this has had negative effects on the populations of the greater sage grouse, the black-tailed rabbit, and the Paiute ground squirrel, prey animals that golden eagles and prairie falcons rely on. Cheatgrass invasions “increase fire frequency by increasing the fuel surface-to-volume ratio, increasing horizontal fuel continuity, and creating a fuel packing ratio that facilitates ignition,” Brooks, et al., 2004. This process can change the normal fire intensity and soil heating that typically occur in the less frequent sagebrush fires, as discontinuous shrubby vegetation is replaced with continuous grasses. The high density of the cheatgrass seed bank exacerbates the problem, further increasing the frequency of the fires. In addition, these fires can be ignited earlier in the spring and later in the fall, thus extending the duration of the fire season.
Brooks, et al., 2004, examined the potential of several other invasive plants to alter fire regimes in Western States and other areas of the world. Invasion by the annual grass, Bromus rubens, red brome, threatens the fire regime in the Mojave Desert, thus increasing the threat to the desert tortoise. Changes to fire regimes can make it even more challenging to restore damaged ecosystems. Brooks, et al., provide recommendations on how to better manage these alterations to the fire cycle.
In my 2017 interview with Slade Franklin, Wyoming Department of Agriculture Weed and Pest Coordinator: I asked what causes cheatgrass to be of such high concern in the west. Slade explained: “Adding cheatgrass to the sagebrush habitat changes a 10-15 year fire cycle to a 1-2 year fire cycle. Sagebrush and other Great Basin and Wyoming desert perennials are on a 10-15 year fire cycle. That means it is typical to have a wildfire in that habitat about every 10-15 years. This longer cycle is important because it takes several years for sagebrush and other perennials to be established. These fires traditionally were not so hot, nor so widespread, as to endanger perennials or their seed bank.
“If cheatgrass is allowed to grow ungrazed, cheatgrass forms fires that tend to burn hotter and are more wide-spread. And, cheatgrass produces much more seed than do the perennials. Because cheatgrass is an annual, it produces seed rapidly.
“Cheatgrass can be an early spring grazing grass, because it is available before the perennial grasses. If you graze livestock on cheatgrass in the early spring, you greatly reduce the amount of cheatgrass that can go to seed, thus reducing both the fire hazard and the seed bank.
“President Obama executed an Executive Order on ‘Strategy Plan on Wildfires’ that pointed out that if we put more money into prevention of wildfires [such as by managing cheatgrass], we can reduce the amount of money we need to spend on wildfires.”
Jim Cochran, District Manager, NRCS, Laramie County Field Office told me: “The BLM [administered by the US Department of the Interior] and the US Forest Service [administered by the USDA] both have a policy about grazing that has backfired and caused an increase in cheatgrass. Cheatgrass, a winter annual grass, is one of the most palatable forages from April to June. But the Federal Agencies don’t allow grazing [on Federal lands] until June through September. If not grazed in the spring, cheatgrass flourishes in the summer, when it becomes unpalatable. It becomes palatable again in October, but by then the grazing leases are finished for the year. Thus, this outmoded Federal grazing policy has been instrumental in causing the spread of cheatgrass.”
Harris, 1967, reviewed decades of research and reports on the reduction of bluebunch wheatgrass and the subsequent spread of cheatgrass in Western States. Bluebunch wheatgrass previously was the dominant native grass species in the intermountain region of the Western US and Canada. Heavy livestock grazing in Eastern Washington facilitated the spread of cheatgrass as early as the 1890s. Cheatgrass also spread in abandoned fields and repeatedly burned areas.
Cheatgrass was likely introduced in the Eastern Coastal States first. It may have then spread West, or it may have been separately introduced into Western States. There were reports of cheatgrass in the US beginning in 1861. It was likely widely scattered in the West by 1893. Cheatgrass now grows in most of the States, but became particularly a problem in the Northwest by the 1960s.
Harris, 1967, demonstrated that cheatgrass, a winter annual, preempts resources from perennial bluebunch wheatgrass. In field and laboratory growth experiments conducted in Western Washington, Harris found that, although both species germinated at about the same time in the fall, cheatgrass had faster winter root growth, while wheatgrass “roots remained dormant until soil temperatures reached 8 to 10 C in late April.” This allowed cheatgrass to dominate in the spring. Cheatgrass has an “inherently greater root elongation rate” and earlier seedling development than bluebunch wheatgrass. Harris also found that because cheatgrass matures four to six weeks earlier than wheatgrass, cheatgrass “stands maintain a heavy demand on soil moisture stores over a wide range of plant densities.”
Harris, 1967, found that cheatgrass completed seeding and began to die back by late May. “After reaching maturity, [cheatgrass] forage becomes unpalatable and low in nutrient value. In this condition it presents a serious fire hazard, and… the sharp-callused seeds may cause blindness and lumpy jaw (actinomycosis) in grazing animals as the result of puncture wounds.” In contrast, bluebunch wheatgrass did not flower until July. In addition, cheatgrass produces many more seeds than does wheatgrass.
Dr. Scott Nissen, from Colorado State University, told me, “Cheatgrass grows abundantly in sagebrush habitat, which is the home to the sage grouse. Sagebrush does not have a soil seed bank because the seeds don’t persist in the soil. So if you have a large fire, it can wipe it out in an area, and there won’t be a seed bank to enable sagebrush to grow back.
“We had two years with El Nino effects, resulting in tons of rain in 2015. This allows cheatgrass to fill in an area very rapidly. We can have massive wildfires, driven by cheatgrass. So next summer [2018] could be the summer when the wildfires would come. I’m studying cheatgrass all along the front range of Colorado and into Wyoming at Pinedale. This herbicide [Alion] may work on any perennial weed that comes from seed. Perhaps it will also work on biennial weeds… Using Alion (Indaziflam) on cheatgrass, we can stop this [increased grassland fires] from occurring… In a good rain year, there’s a lot of good native grass coming in, from heavy summer rains. But we’re not getting those summer rains anymore.”
As it alters the fire regime, increasing the frequency of fires, cheatgrass also alters the structure and function of the sagebrush habitat, converting a habitat dominated by forbs, shrubs, and perennial grasses, into a habitat dominated by annual grasses. “Cheatgrass probably has the most widespread and severe effects on wildlife of any invasive plant” (Sheley, et al., 2011). As of 2011, cheatgrass was estimated to cover 40 million ha in the Intermountain West. These changes to the habitat affect various rare species, including five rare bird species and the pygmy rabbit, as well as numerous other bird and mammal species that rely on sagebrush habitat for food, shelter, and nesting.
Coates, et al., 2016, examined 30 years of sage grouse population data, wildfire and climate data in the Great Basin. They found that the increased size and frequency of rangeland wildfires has not only contributed to the decline of sagebrush habitat and populations of the greater sage grouse, but also have made it more challenging for sagebrush habitat to recover. They estimate that sage grouse populations will continue to decline to 43% of current numbers over the next three decades. They advocate for fire suppression within the rangelands, to reduce the impacts of cheatgrass-related fires. Ironically, in the past, prescribed fire was proposed as a tool to improve sage grouse habitat, but we now know it is a detriment to sagebrush habitat.
Sheley, et al., 2011, concluded that, due to the greater frequency of rangeland fires, “fire suppression is required to allow native species to compete against cheatgrass and other fire-tolerant invaders.” Ironically, while fire suppression in the national forests has resulted in greater forest fire risk over time, within cheatgrass invaded rangelands, suppressing rangeland fires may be necessary. Depending on the cause of the cheatgrass invasion, multiple methods will likely be needed to suppress cheatgrass.
Bradley, et al., 2018, created models of the extent of cheatgrass cover in the Intermountain West, using satellite imagery and data from thousands of field surveys. They found that “cheatgrass achieves > 15% cover over 210,000 km2 (31%) of the Intermountain West.” They also found that “fire probability increased rapidly at low cheatgrass cover (1-5%) but remained similar at higher cover, suggesting that even small amounts of cheatgrass in an ecosystem can increase fire risk.” They also learned that cheatgrass is associated with a ten days earlier fire seasonality, and that the presence of cheatgrass doubles the fire frequency in the Great Basin. In addition, cheatgrass dominated areas were four times more likely to burn multiple times between 2000 and 2015, and many fires resulted from human ignitions, such as fireworks.
Pilliod, et al., 2017, “found that both native and non‐native grasses and forbs influence the number of fires and area burned suggesting that cheatgrass is not the sole driver of the grass–fire cycle in [the Great Basin]. Second, we found support for our hypothesis that years with more fires and area burned tend to occur after one or more years of above‐average precipitation. This could be explained by the accumulation of persistent litter, which increases fuel loads through time. This suggests that precipitation patterns may act indirectly on fire through mechanisms of vegetation and litter production and these indirect effects may be time lagged by 1–3 years as fine fuels accumulate and conditions are right for combustion and fire spread…. Our findings suggest that land managers interested in reducing fine fuels may need to consider how to manage previous years’ herbaceous production, in the form of litter from annual forbs and cheatgrass, instead of solely managing biomass from the current growing season.”
The history of the use of cheatgrass or downy brome (Bromus tectorum, previously known as Anisantha tectorum) as livestock forage is useful to note. In the 1945 archival minutes from the Western Weed Control Conference, Mr. Thomas H. Van Meter, from the US Forest Service, stationed in Idaho, gave a report on “Noxious Weed Control on National Forests.” He expressed some concerns about the recent spread of medusa-head in California. He stated that, “It is not a desireable forage, when compared with Bromus tectorum, and medusa-head also poses a greater fire risk. Medusa-head has the potential to become a serious problem on range lands.”
DiTomaso, et al., 2017, describe the annual bromes as the most challenging invaders in U.S. rangelands today. Cheatgrass or downy brome “now infests 23 million hectares… and 28% of all non-Federal rangelands… Downy brome was first introduced to the western USA in 1861, and by the early 1900s was widely distributed in many rangelands, particularly… [sagebrush] ecosystems…[where it has] altered the natural fire regime to replace native, perennial species as the dominant vegetation.”
References:
Previous sections on Wildfires:
Next sections on "Defining the Problem":
Rangeland fires
Many forests are actually classified as types of rangeland, but for this section, I will use “rangeland” in the more common usage, in reference to the non-forested ecosystems of the Western States. Western rangelands include grasslands, prairies, sagebrush steppes, and deserts. Refer to the section “Rangeland Restoration” for details on some restoration projects within those ecosystems.
Native Americans have used controlled burns on rangelands for centuries before Anglo-Americans came onto the scene. In recent years rangeland fires have increased dramatically. These fires, occurring mainly in Western States, such as in the Great Basin and other areas, receive much less attention, both in the news media and in Federal agencies, due to the relatively low human populations in these areas. But there is a widening extent of the damages, especially to natural ecosystems, due to these fires.
Recent wildfire seasons have punctuated the critical need to reduce wildfires. In summer 2017, for example, a number of Western States, including Montana, exhausted their State funds to fight wildfires long before the fire season came to an end. And in warmer, southern states, such as California, the summer fire season extended well into late fall.
According to an article by Nick Bowlin, 2019, “Historically, sagebrush habitat burned about once every century or less, but now it happens every five to 10 years. Over the past two decades, more than 15 million acres of sagebrush have been permanently lost to wildfire.” Since 2000, more acreage has been lost to shrubland or grassland fires than to forest fires. Sagebrush habitat is host to about 350 species of native plants and wildlife. Greater sage grouse habitat has been reduced to near extinction levels. “The fires also harm watersheds, cause erosion, and destroy wildlife corridors used by pronghorn antelope, mule deer and elk.”
Many rural counties and many ranches suffer infrastructure damage and livestock losses from these fires. There are fewer Federal funds to assist with managing rangelands, in comparison to farmlands and forests. The BLM, which manages public rangelands, is severely underfunded, in comparison to the US Forest Service, even though the BLM manages 50 million more acres of public land than does the Forest Service.
What are the factors that are increasing the number and intensity of rangeland fires?
Climate change
Natural drought patterns are becoming exacerbated by global climate change. Recent high summer temperatures and drought, both exacerbated by climate change, have resulted in the hottest, driest summers, particularly in Western States, in recorded history. In the Western US, higher temperatures, combined with fire suppression policies, and the large increase in agricultural monocultures has allowed fires to become a greater problem every summer. All the climate-related problems described above are also creating problems in the non-forested regions of the West.
Invasive plants: Role in rangeland wildfires
Invasive plant species have the potential to alter various aspects of fire regimes, and thus can permanently alter ecosystems. As sagebrush ecosystems in the West have been decreased due to over-grazing, expansion of agriculture, and expansion of human populations, cheatgrass and other invasive plant species have expanded into the rangelands.
Cheatgrass, Bromus tectorum, long a popular forage, and an annual, non-native grass, is now being viewed as an invasive species in many areas of the West. Because it is still used as forage, it is not included on most State lists of noxious weeds, and it is not included on the Federal list of invasive species. However, several Western States (California, Colorado, Montana, New Mexico) have now included it as a noxious weed that is widespread and needs to be monitored and researched, to limit its spread. And a few Counties in Western States have added it to the County noxious weed list. Controlling its spread to reduce rangeland wildfires is becoming a priority in Western States.
Brooks, et al., 2004, state that the spread of cheatgrass across Western States has increased the frequency of rangeland fires “to the point that native shrub-steppe species cannot recover.” In sagebrush steppe habitats, this has had negative effects on the populations of the greater sage grouse, the black-tailed rabbit, and the Paiute ground squirrel, prey animals that golden eagles and prairie falcons rely on. Cheatgrass invasions “increase fire frequency by increasing the fuel surface-to-volume ratio, increasing horizontal fuel continuity, and creating a fuel packing ratio that facilitates ignition,” Brooks, et al., 2004. This process can change the normal fire intensity and soil heating that typically occur in the less frequent sagebrush fires, as discontinuous shrubby vegetation is replaced with continuous grasses. The high density of the cheatgrass seed bank exacerbates the problem, further increasing the frequency of the fires. In addition, these fires can be ignited earlier in the spring and later in the fall, thus extending the duration of the fire season.
Brooks, et al., 2004, examined the potential of several other invasive plants to alter fire regimes in Western States and other areas of the world. Invasion by the annual grass, Bromus rubens, red brome, threatens the fire regime in the Mojave Desert, thus increasing the threat to the desert tortoise. Changes to fire regimes can make it even more challenging to restore damaged ecosystems. Brooks, et al., provide recommendations on how to better manage these alterations to the fire cycle.
In my 2017 interview with Slade Franklin, Wyoming Department of Agriculture Weed and Pest Coordinator: I asked what causes cheatgrass to be of such high concern in the west. Slade explained: “Adding cheatgrass to the sagebrush habitat changes a 10-15 year fire cycle to a 1-2 year fire cycle. Sagebrush and other Great Basin and Wyoming desert perennials are on a 10-15 year fire cycle. That means it is typical to have a wildfire in that habitat about every 10-15 years. This longer cycle is important because it takes several years for sagebrush and other perennials to be established. These fires traditionally were not so hot, nor so widespread, as to endanger perennials or their seed bank.
“If cheatgrass is allowed to grow ungrazed, cheatgrass forms fires that tend to burn hotter and are more wide-spread. And, cheatgrass produces much more seed than do the perennials. Because cheatgrass is an annual, it produces seed rapidly.
“Cheatgrass can be an early spring grazing grass, because it is available before the perennial grasses. If you graze livestock on cheatgrass in the early spring, you greatly reduce the amount of cheatgrass that can go to seed, thus reducing both the fire hazard and the seed bank.
“President Obama executed an Executive Order on ‘Strategy Plan on Wildfires’ that pointed out that if we put more money into prevention of wildfires [such as by managing cheatgrass], we can reduce the amount of money we need to spend on wildfires.”
Jim Cochran, District Manager, NRCS, Laramie County Field Office told me: “The BLM [administered by the US Department of the Interior] and the US Forest Service [administered by the USDA] both have a policy about grazing that has backfired and caused an increase in cheatgrass. Cheatgrass, a winter annual grass, is one of the most palatable forages from April to June. But the Federal Agencies don’t allow grazing [on Federal lands] until June through September. If not grazed in the spring, cheatgrass flourishes in the summer, when it becomes unpalatable. It becomes palatable again in October, but by then the grazing leases are finished for the year. Thus, this outmoded Federal grazing policy has been instrumental in causing the spread of cheatgrass.”
Harris, 1967, reviewed decades of research and reports on the reduction of bluebunch wheatgrass and the subsequent spread of cheatgrass in Western States. Bluebunch wheatgrass previously was the dominant native grass species in the intermountain region of the Western US and Canada. Heavy livestock grazing in Eastern Washington facilitated the spread of cheatgrass as early as the 1890s. Cheatgrass also spread in abandoned fields and repeatedly burned areas.
Cheatgrass was likely introduced in the Eastern Coastal States first. It may have then spread West, or it may have been separately introduced into Western States. There were reports of cheatgrass in the US beginning in 1861. It was likely widely scattered in the West by 1893. Cheatgrass now grows in most of the States, but became particularly a problem in the Northwest by the 1960s.
Harris, 1967, demonstrated that cheatgrass, a winter annual, preempts resources from perennial bluebunch wheatgrass. In field and laboratory growth experiments conducted in Western Washington, Harris found that, although both species germinated at about the same time in the fall, cheatgrass had faster winter root growth, while wheatgrass “roots remained dormant until soil temperatures reached 8 to 10 C in late April.” This allowed cheatgrass to dominate in the spring. Cheatgrass has an “inherently greater root elongation rate” and earlier seedling development than bluebunch wheatgrass. Harris also found that because cheatgrass matures four to six weeks earlier than wheatgrass, cheatgrass “stands maintain a heavy demand on soil moisture stores over a wide range of plant densities.”
Harris, 1967, found that cheatgrass completed seeding and began to die back by late May. “After reaching maturity, [cheatgrass] forage becomes unpalatable and low in nutrient value. In this condition it presents a serious fire hazard, and… the sharp-callused seeds may cause blindness and lumpy jaw (actinomycosis) in grazing animals as the result of puncture wounds.” In contrast, bluebunch wheatgrass did not flower until July. In addition, cheatgrass produces many more seeds than does wheatgrass.
Dr. Scott Nissen, from Colorado State University, told me, “Cheatgrass grows abundantly in sagebrush habitat, which is the home to the sage grouse. Sagebrush does not have a soil seed bank because the seeds don’t persist in the soil. So if you have a large fire, it can wipe it out in an area, and there won’t be a seed bank to enable sagebrush to grow back.
“We had two years with El Nino effects, resulting in tons of rain in 2015. This allows cheatgrass to fill in an area very rapidly. We can have massive wildfires, driven by cheatgrass. So next summer [2018] could be the summer when the wildfires would come. I’m studying cheatgrass all along the front range of Colorado and into Wyoming at Pinedale. This herbicide [Alion] may work on any perennial weed that comes from seed. Perhaps it will also work on biennial weeds… Using Alion (Indaziflam) on cheatgrass, we can stop this [increased grassland fires] from occurring… In a good rain year, there’s a lot of good native grass coming in, from heavy summer rains. But we’re not getting those summer rains anymore.”
As it alters the fire regime, increasing the frequency of fires, cheatgrass also alters the structure and function of the sagebrush habitat, converting a habitat dominated by forbs, shrubs, and perennial grasses, into a habitat dominated by annual grasses. “Cheatgrass probably has the most widespread and severe effects on wildlife of any invasive plant” (Sheley, et al., 2011). As of 2011, cheatgrass was estimated to cover 40 million ha in the Intermountain West. These changes to the habitat affect various rare species, including five rare bird species and the pygmy rabbit, as well as numerous other bird and mammal species that rely on sagebrush habitat for food, shelter, and nesting.
Coates, et al., 2016, examined 30 years of sage grouse population data, wildfire and climate data in the Great Basin. They found that the increased size and frequency of rangeland wildfires has not only contributed to the decline of sagebrush habitat and populations of the greater sage grouse, but also have made it more challenging for sagebrush habitat to recover. They estimate that sage grouse populations will continue to decline to 43% of current numbers over the next three decades. They advocate for fire suppression within the rangelands, to reduce the impacts of cheatgrass-related fires. Ironically, in the past, prescribed fire was proposed as a tool to improve sage grouse habitat, but we now know it is a detriment to sagebrush habitat.
Sheley, et al., 2011, concluded that, due to the greater frequency of rangeland fires, “fire suppression is required to allow native species to compete against cheatgrass and other fire-tolerant invaders.” Ironically, while fire suppression in the national forests has resulted in greater forest fire risk over time, within cheatgrass invaded rangelands, suppressing rangeland fires may be necessary. Depending on the cause of the cheatgrass invasion, multiple methods will likely be needed to suppress cheatgrass.
Bradley, et al., 2018, created models of the extent of cheatgrass cover in the Intermountain West, using satellite imagery and data from thousands of field surveys. They found that “cheatgrass achieves > 15% cover over 210,000 km2 (31%) of the Intermountain West.” They also found that “fire probability increased rapidly at low cheatgrass cover (1-5%) but remained similar at higher cover, suggesting that even small amounts of cheatgrass in an ecosystem can increase fire risk.” They also learned that cheatgrass is associated with a ten days earlier fire seasonality, and that the presence of cheatgrass doubles the fire frequency in the Great Basin. In addition, cheatgrass dominated areas were four times more likely to burn multiple times between 2000 and 2015, and many fires resulted from human ignitions, such as fireworks.
Pilliod, et al., 2017, “found that both native and non‐native grasses and forbs influence the number of fires and area burned suggesting that cheatgrass is not the sole driver of the grass–fire cycle in [the Great Basin]. Second, we found support for our hypothesis that years with more fires and area burned tend to occur after one or more years of above‐average precipitation. This could be explained by the accumulation of persistent litter, which increases fuel loads through time. This suggests that precipitation patterns may act indirectly on fire through mechanisms of vegetation and litter production and these indirect effects may be time lagged by 1–3 years as fine fuels accumulate and conditions are right for combustion and fire spread…. Our findings suggest that land managers interested in reducing fine fuels may need to consider how to manage previous years’ herbaceous production, in the form of litter from annual forbs and cheatgrass, instead of solely managing biomass from the current growing season.”
The history of the use of cheatgrass or downy brome (Bromus tectorum, previously known as Anisantha tectorum) as livestock forage is useful to note. In the 1945 archival minutes from the Western Weed Control Conference, Mr. Thomas H. Van Meter, from the US Forest Service, stationed in Idaho, gave a report on “Noxious Weed Control on National Forests.” He expressed some concerns about the recent spread of medusa-head in California. He stated that, “It is not a desireable forage, when compared with Bromus tectorum, and medusa-head also poses a greater fire risk. Medusa-head has the potential to become a serious problem on range lands.”
DiTomaso, et al., 2017, describe the annual bromes as the most challenging invaders in U.S. rangelands today. Cheatgrass or downy brome “now infests 23 million hectares… and 28% of all non-Federal rangelands… Downy brome was first introduced to the western USA in 1861, and by the early 1900s was widely distributed in many rangelands, particularly… [sagebrush] ecosystems…[where it has] altered the natural fire regime to replace native, perennial species as the dominant vegetation.”
References:
- Bowlin, N. (June 24, 2019). The West’s worst fires aren’t burning in forests. High Country News, 8.
- Bradley, B.B., Curtis, C.A., Fusco, E.J., Abatzoglou, J.T., Balch, J.K., Dadashi, S., & Tuanmu, M. (2018). Cheatgrass (Bromus tectorum) distribution in the intermountain Western United States and its relationship to fire frequency, seasonality, and ignitions. Biological invasions, 20:1493-1506. https://doi.org/10.1007/s10530-017-1641-8
- Brooks, M.L., D’Antonio, C.M., Richardson, D.M., Grace, J.B., Keeley, J.E., DiTomaso, J.M., Hobbs, R.J., Pellant, M., & Pyke, D. (July, 2004). Effects of invasive alien plants on fire regimes. BioScience, 54 (7):677-688.
- Coates, P.S., et al. (Nov., 8, 2016). Wildfire, climate, and invasive grass interactions negatively impact an indicator species by reshaping sagebrush ecosystems. Proceedings of the National Academy of Sciences of the USA, 113(45):12745-12750.
- DiTomaso, J.M., Monaco, T.A., James, J.J., Firn, J. (2017). Invasive plant species and novel rangeland systems. In D. Briske (Ed.), Rangeland Systems: Processes, Management & Challenges: 429-465. Springer Series on Environmental Management. Springer, Cham.
- Harris, G.A. (1967). Some competitive relationships between Agropyron spicatum and Bromus tectorum. Ecological Monographs, 37: 89-111.
- Pilliod, D.S., Welty, J.L., & Arkle, R.S. (Oct., 2017). Refining the cheatgrass-fire cycle in the Great Basin: Precipitation timing and fine fuel composition predict wildfire trends. Ecology and Evolution, 7(19):8126-8151. Doi: 10.1002/ece3.3414
- Sheley, R.L., James, J.J., Rinella, M. J., Blumenthal, D., & DiTomaso, J.M. (2011). Invasive plant management on anticipated conservation benefits: A scientific assessment. In D.D. Briske (Ed.) Conservation benefits of rangeland practices: Assessment, recommendation, and knowledge gaps. (pp. 293-336). USDA Natural Resources Conservation Service.
Previous sections on Wildfires:
Next sections on "Defining the Problem":