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Alpha diversity (Shannon's index of proportional abundance, Pielou's index of evenness, and the number of species per plot), beta diversity (Whittaker's index—the values are a unitless index of dissimilarity), and native and exotic plant cover, all grouped by fire frequency. Shading indicates significantly different groups as determined by Tukey's test.
Source publication
Sagebrush is one of the most imperiled ecosystems in western North America, having lost about half of its original 62 million hectare extent. Annual grass invasions are known to be increasing wild-fire occurrence and burned area, but the lasting effects (greater than five years post-fire) that the resulting reburns have on these plant communities a...
Similar publications
Exotic annual grass invasion and dominance of rangelands is a concern across western North America and other semiarid and arid ecosystems around the world. Postfire invasion and dominance by exotic annual grasses in sagebrush communities is especially problematic as there are no cost-effective control strategies available for the vast acreages alre...
Wildfire size and frequency have increased in the western United States since the 1950s, but it is unclear how seeding treatments have altered fire regimes in arid steppe systems. We analyzed how the number of fires since 1955 and the fire return interval and frequency between 1995 and 2015 responded to seeding treatments, anthropogenic features, a...
Citations
... For the probability of presence, we fit covariates with a cloglog link function including sagebrush ( sage i,−1 ), annual herbaceous ( annug i,−1 ), and perennial herbaceous ( pereg i,−1 ) cover in the year before project initiation (i.e., before first fire or initial project grid points), cumulative number of burns ( sum_burn i,t ), and soil moisture ( soil i ). Vegetation cover and soil moisture were therefore static in time, indicating the general site condition for sagebrush presence, whereas cumulative number of burns represented a dynamic condition depending on occurrence of repeated wildfire (Mahood and Balch 2019). We also specified an interaction between perennial herbaceous cover and soil moisture because effects of native grass cover can shift from facilitative to competitive depending on soil climatic conditions (Chambers et al. 2014b;Roundy and Chambers 2021). ...
... We evaluated influence of environmental factors on sagebrush cover with two joint processes, including probability of sagebrush presence, and trends in sagebrush cover given presence. Consistent with previous field studies, we found sagebrush presence was positively associated with the amount of initial (pre-project) sagebrush cover (Eiswerth et al. 2009;Arkle et al. 2022) and negatively with initial annual herbaceous cover and cumulative number of burns (Eiswerth et al. 2009;Mahood and Balch 2019). ...
Context
Widespread ecological degradation has prompted calls for massive global investments in ecological restoration, yet limited resources necessitate efficient application of restoration efforts. In western North America, altered fire regimes are increasing the scale of restoration needed to preserve the sagebrush (Artemisia species) biome but prioritizing and implementing effective restoration is complicated by the vast and heterogeneous sagebrush landscape, which includes gradients in climate, disturbance, and species composition.
Objectives
To develop spatially explicit and context-dependent estimates of treatment efficacy and sagebrush recovery rates.
Methods
We leveraged a suite of spatio-temporally extensive datasets to evaluate the influence of restoration treatments and environmental conditions on trends in post-disturbance sagebrush cover, with an emphasis on understanding differences between sites recovering naturally and sites receiving restoration treatments. We used estimates from these models to develop spatially explicit projections for sagebrush recovery, conditional on disturbance, restoration practice, and environmental conditions.
Results
We found seeding Artemisia spp. increased sagebrush cover over time relative to natural recovery, but this relationship depended on spring soil moisture availability and treatment methods. Natural recovery was positively influenced by soil moisture and sagebrush cover and negatively influenced by cumulative burns and annual herbaceous cover, while the influence of perennial herbaceous cover varied with soil moisture.
Conclusions
Our results provide biome-wide insights and spatially explicit tools that can inform economic cost-effectiveness analyses, restoration prioritization tools, and other scientific endeavors to ensure managers have the tools and information needed to effectively steward the sagebrush biome in a rapidly changing world.
... However, changes in the severity of disturbance events are likely to weaken community-level resistance and facilitate B. tectorum dominance (Bradford and Lauenroth 2006;Kroel-Dulay et al. 2015). Fire is of particular concern, as B. tectorum can rapidly establish following fire and then substantially increase fire frequencies afterwards (Balch et al. 2013;Davies and Nafus 2013;Bradley et al. 2018;Mahood and Balch 2019). Climate change-mediated increases in drought severity are also projected to reduce biotic resistance from native perennial grasses, potentially facilitating B. tectorum dominated state (Bradley 2009). ...
Bromus tectorum invasion degrades biodiversity and ecosystem functioning in the Great Basin Desert. To explain, predict, and manage B. tectorum invasion, we must understand the biotic and abiotic factors that influence its establishment and persistence. We explored interactions between two key constraints for invaders in general and B. tectorum in particular: post-dispersal seed predation and climate, including mean annual temperature, rainfall, snowfall, and aridity. At six study sites in undisturbed, climax Artemisia tridentata communities across northern Nevada and Utah, we performed one-time additions of 100 B. tectorum seeds to microsites outfitted with either a dummy (“open”) cage that exposed seeds to rodent foraging, or a functional (“closed”) cage that protected them from rodent foraging. Living Bromus tectorum plants within experimental cages were censused one and 5 years after seed additions. At both 1- and 5-years censuses, and regardless of climate, B. tectorum densities were similar in open and closed microsites, suggesting that rodent foraging did not affect B. tectorum establishment or persistence. Compared to 1-year censuses, B. tectorum counts declined by 47% across all sites after 5 years, but declines were sharpest at sites with the highest mean annual temperatures. Taken together, our findings suggest that undisturbed, climax A. tridentata communities can resist B. tectorum expansion, and this resistance increases with mean annual temperature, not rodent foraging. We suggest that controlling nascent populations of B. tectorum may be particularly urgent in intact climax A. tridentata communities in relatively cool climates, where community-level resistance against B. tectorum persistence is lowest.
... Annual grasses are more flammable and dry out up to 1 mo earlier than large bunchgrasses ( Davies and Nafus 2013 ). Breaking the invasive annual grass-fire cycle is critically important for the recovery of fire-intolerant species, such as sagebrush, as well as to reduce the likelihood of losing more perennial vegetation ( Mahood and Balch 2019 ). Seeding only locally sourced native bunchgrasses after fire, followed 3 yr later by pre-emergent herbicide application, increased perennial vegetation in these plant communities, an important first step toward recovering perennial dominance. ...
... Annual grasses can also negatively affect native perennial vegetation by increasing the amount and continuity of highly flammable fine fuels (Davies & Nafus, 2013;Knapp, 1995) and ultimately promoting more frequent fires (Brooks et al., 2004;D'Antonio & Vitousek, 1992). More frequent fire regimes exclude sagebrush and negatively affect most native perennial plants, favoring invasive annual grasses and often leading to the development of a positive biofeedback between annual grasses and fire (D'Antonio & Vitousek, 1992;Eiswerth et al., 2009;Ellsworth et al., 2020;Mahood & Balch, 2019). ...
There are concerns about the negative consequences of non‐native livestock grazing of sagebrush communities, especially since these communities are experiencing unpreceded threats from invasive annual grasses, altered fire regimes, and climate change. The narrative around grazing often focuses on the effects of heavy, repeated growing season use that were common historically but now are rare or localized (e.g., near water sources). At the same time, the potential for ecological benefits of strategically applied grazing is often overlooked, limiting management options that may promote desired outcomes. To improve management in the face of unprecedented threats, we synthesized the literature to investigate and identify potential ecological benefits of strategically applied livestock grazing in sagebrush communities. We found that grazing can be used to modify fine fuel characteristics in ways that decrease fire probability and severity in sagebrush communities. Pre‐fire moderate grazing may be especially important because it decreases fire severity and, thereby, promotes biodiversity and reduces postfire annual grass invasion, fire‐induced mortality of native bunchgrasses, and fire damage to soil biocrusts. Grazing can create and maintain fine fuel breaks to improve firefighter safety and fire suppression efficiency. Strategic grazing can also be used to promote desirable plant community composition. Grazing can be a valuable tool, that is currently underutilized, for achieving desired management outcomes in the sagebrush and likely other ecosystems. Improper grazing can generate severe negative consequences; therefore, successful application of grazing to achieve desired outcomes will require careful attention to plant community response and balancing management objectives with community constraints.
... This fire-induced heterogeneity could increase diversity at the regional scale, affecting forest and livestock productivity in the area (Scholes and Walker 1993;Huston 1998;Zinck et al. 2010;Cesca et al. 2014;Burkle et al. 2015). However, the positive effect of fire on landscape diversity appears to be associated with fires of low severity and small size (Zinck et al. 2010;Miller and Safford 2020), while landscape diversity decreases in areas with high severity or recurrent extended fires (Mahood and Balch 2019;Zinck et al. 2010;Moghli et al. 2022). In contrast, the effect of fire on local diversity is variable and cannot be clearly established at smaller spatial scales (Giorgis et al. 2021). ...
... In contrast, the effect of fire on local diversity is variable and cannot be clearly established at smaller spatial scales (Giorgis et al. 2021). However, frequent and severe fires have been observed to reduce alpha diversity, particularly of woody species (Mahood and Balch 2019). Besides, fire recurrence has been observed to reduce many ecosystem services and ecosystem multifunctionality, effects that can be buffered in areas with long post-fire recovery times (Moghli et al. 2022). ...
Background Natural and anthropogenic wildfires burn large areas of arid and semi-arid forests with significant socioeconomic and environmental impacts. Fire regimes are controlled by climate, vegetation type, and anthropo-genic factors such as ignition sources and human-induced disturbances. Projections of climate and land-use change suggest that these controlling factors will change, altering fire regimes in the near future. In the southern Central Monte, Mendoza, Argentina, the factors that modulate the fire temporal and spatial variability are poorly understood. We reconstructed the fire history of southeast of Mendoza from 1984 to 2023 and investigated the relationships between fire extent and climate variability at seasonal and interannual scales. Burned areas were determined using Google Earth Engine by processing Landsat 5-TM, Landsat 7-ETM+ , and Landsat 8-OLI-TIRS sensor imagery. Results The region exhibited high spatial and temporal variability in fire occurrence, being a mosaic of areas with different fire histories and recovery times. Between 1985 and 2023, fire recurrence ranged from sites unburned to sites with up to 14 fires. The occurrence of large fires was strongly favored by a combination of a year with abundant spring-early summer precipitation, which favors fuel accumulation, followed by a year of low spring-early summer precipitation. Precipitation and burnt area showed a very pronounced 6-7 year cycle, suggesting a dominant climatic control on fire occurrence. Conclusions Fire distribution in southeastern Mendoza forests is not homogeneous, resulting in a mosaic of patches with different fire histories. This heterogeneity may be related to vegetation patterns and land use. The temporal variability of fires is strongly influenced by climate variability, which would promote fuel production and subsequent drying. Large fires are concentrated in periods of high interannual precipitation variability. Climate change scenarios predict an increase in temperature and precipitation variability in the region, suggesting future changes in fire dynamics. Our results contribute to the development of fire guidelines for southeastern Mendoza forests, focusing on periods of wet years followed by dry years that favor fire occurrence and spread.
... Negative Recent increases in annual forbs and grasses are generally associated with the large-scale invasion of nonnative species such as cheatgrass (Bromus tectorum), which are degrading sagebrush habitat across much of western North America (Balch et al., 2013;Mahood and Balch, 2019). Winter precipitation Negative Winter precipitation is associated with snow cover and depth, which can decrease pronghorn mobility and increase foraging energy expenditure leading to higher mortality (Barrett, 1982;Reinking et al., 2019;Smith et al., 2020;Taylor et al., 2016). ...
... Spring precipitation Positive Increased spring precipitation results in higher quality and quantity of forage and higher pronghorn densities (Brown et al., 2006;Gedir et al., 2015) Roads Negative Roads fragment habitat and facilitate movement of predators and hunters (Gamo et al., 2017;Hebblewhite et al., 2009;Popp and Donovan, 2016;Seidler et al., 2015). Oil and gas development Negative Oil and gas development is associated with habitat loss both directly and through fragmentation which can lead to habitat abandonment and lower pronghorn abundance (Christie et al., 2015;Sawyer et al., 2019) Fire Mixed Fires can degrade sagebrush habitat (Balch et al., 2013;Mahood and Balch, 2019); however, they also reduce tree cover to restore rangeland habitat impacted by woody encroachment (Bielski et al., 2021;Donovan et al., 2020b). Pronghorn have been shown to utilize recently burned areas (Augustine and Derner, 2015;Courtney, 1989). ...
Conservation is increasingly focused on preventing losses in species’ populations before they occur. Tracking changes in demographic parameters that can impact a population’s resilience in response to drivers of global change can support early conservation efforts. We assessed trends in population productivity (late summer juveniles per 100 females) relative to drivers of global change in 40 pronghorn (Antilocapra americana) herds across sagebrush (Artemisia spp.) steppe in Wyoming. Pronghorn are an iconic rangeland species that have been exposed to increasing levels of anthropogenic, climatic, and land-use change. Using data collected across the state of Wyoming, we (1) assessed long-term trends in population productivity, (2) identified patterns in large-scale drivers of global change (i.e., climate, land cover change) across pronghorn habitat,
and (3) determined the relationship between drivers of global change and population productivity over a 35-year (1984–2019) period. While Wyoming hosts some of the most abundant populations of pronghorn in North America that have been largely stable in recent years, we found many herds are experiencing long-term declines in productivity. Long-term declines in productivity were associated with increases in oil and gas development and woody encroachment. Although increasing across almost all herd units, woody vegetation cover remains at low levels, suggesting that pre-emptive management may help to prevent losses in pronghorn populations.
... One factor that leads to more frequent fire in systems where fire was infrequent historically is that of invasive grasses (D'Antonio et al., 2011;D'Antonio & Vitousek, 1992). These grasses may form self-reinforcing positive feedback loops with fire, in which fire area increases and return interval decreases as a result of increased fuel (provided by the grasses), which then benefits grasses relative to native plant species that may not be as well adapted to fire (Ellsworth et al., 2014;Mahood & Balch, 2019;Smith & Tunison, 1992). This feedback loop may result in species-poor alternative stable states where one of the major components is the cover of invasive grasses (D'Antonio et al., 2011;Hamilton et al., 2021;Smith & Tunison, 1992;Yelenik & D'Antonio, 2013). ...
Ecological restoration is beneficial to ecological communities in this era of large‐scale landscape change and ecological disruption. However, restoration outcomes are notoriously variable, which makes fine‐scale decision‐making challenging. This is true for restoration efforts that follow large fires, which are increasingly common as the climate changes.
Post‐fire restoration efforts, like tree planting and seeding have shown mixed success, though the causes of the variation in restoration outcomes remain unclear. Abiotic factors such as elevation and fire severity, as well as biotic factors, such as residual canopy cover and abundance of competitive understorey grasses, can vary across a burned area and may all influence the success of restoration efforts to re‐establish trees following forest fires.
We examined the effect of these factors on the early seedling establishment of a tree species—māmane ( Sophora chrysophylla )—in a subtropical montane woodland in Hawaiʻi. Following a human‐caused wildfire, we sowed seeds of māmane as part of a restoration effort. We co‐designed a project to examine māmane seedling establishment.
We found that elevation was of overriding importance, structuring total levels of plant establishment, with fewer seedlings establishing at higher elevations. Residual canopy cover was positively correlated with seedling establishment, while cover by invasive, competitive understorey grasses very weakly positively correlated with increased seedling establishment.
Our results point to specific factors structuring plant establishment following a large fire and suggest additional targeted restoration actions within this subtropical system. For example, if greater native woody recruitment is a management goal, then actions could include targeted seed placement at lower elevations where establishment is more likely, increased seeding densities at high elevation where recruitment rates are lower, and/or invasive grass removal prior to seeding. Such actions may result in faster native ecosystem recovery, which is a goal of local land managers.
... Our data show that a second fire occurrence did not significantly alter plant biomass, cover, or density, when compared to the effects of the initial fire ( Fig. 1). Initial desert fires remove significant shrub cover, leaving space and soil resources that promote invasion success that leads to loss of plant community diversity (Brooks 2000, DeFalco et al. 2003Mahood and Balch 2019). The secondary fires occurred 5 years after the initial burns, which is within the potential fire frequency window being observed in these deserts (Balch et al. 2013). ...
Background
Wildfire regimes are changing dramatically across North American deserts with the spread of invasive grasses. Invasive grass fire cycles in historically fire-resistant deserts are resulting in larger and more frequent wildfire. This study experimentally compared how single and repeat fires influence invasive grass-dominated plant fuels in the Great Basin, a semi-arid, cold desert, and the Mojave, a hyper-arid desert. Both study sites had identical study designs. In the summer of 2011, we experimentally burned half of each experimental block, the other half remaining as an unburned control. Half of the burned plots were reburned 5 years later to simulate increasing burn frequency. We estimated non-woody plant biomass, cover, and density in plots from 2017 to 2020.
Results
Biomass did not vary between sites, but there was higher plant cover and lower plant density at the Mojave site than at the Great Basin site. Plant biomass, density, and cover varied significantly across the years, with stronger annual fluctuations in the Great Basin. At both desert sites, fire increased plant density and biomass but had no effect on the cover. The effect of fire on plant cover varied significantly between years for both deserts but was greater in the Great Basin than in the Mojave site. Repeat fires did not amplify initial fire effects.
Conclusions
The results suggest that in general annual fluctuations in fine fuel production and fluctuations in response to fire were more apparent at the Great Basin site than at the Mojave site, with no immediate compounding effect of repeat fires at either site.
... This implies a dynamic whereby communities enter the grass-fire cycle abruptly following fire and dominance of annual grasses is maintained through repeated burning. This paradigm is pervasive, with many emphasizing the importance of fire as a driver of change (Barker et al., 2019;Mahood and Balch, 2019). The spread of annual grass dominance has been attributed to fires igniting in heavily infested communities and spreading into adjacent, intact communities (Balch et al., 2013). ...
Sagebrush ecosystems of western North America are experiencing widespread loss and degradation by invasive annual grasses. Positive feedbacks between fire and annual grasses are often invoked to explain the rapid pace of these changes, yet annual grasses also appear capable of achieving dominance among vegetation communities that have not burned for many decades. Using a dynamic, remotely-sensed vegetation dataset in tandem with remotely-sensed fire perimeter and burn severity datasets, we examine the role of fire in transitions to and persistence of annual grass dominance in the U.S. Great Basin over the past 3 decades. Although annual grasses and wildfire are so tightly associated that one is rarely mentioned without the other, our findings reveal surprisingly widespread transformation of sagebrush ecosystems by invasive annual grasses in the absence of fire. These findings are discussed in the context of strategic management; we argue a pivot from predominantly reactive management (e.g., aggressive fire suppression and post-fire restoration in heavily-infested areas) to more proactive management (e.g., enhancing resistance and managing propagule pressure in minimally-invaded areas) is urgently needed to halt the loss of Great Basin sagebrush ecosystems.
... Once covering more than 600,000 km 2 , 60-90% of the sagebrush steppe has been lost, fragmented, or degraded (Noss et al. 1995;Knick et al. 2003). Due to these disturbances, the sagebrush steppe ecosystem is facing a loss in native plant species and genetic diversity (McArthur & Fairbanks 2001;Mahood & Balch 2019), resulting in reduced ecosystem services such as water and soil retention and plant productivity (Kachergis et al. 2011;Nichols et al. 2021). These changes also threaten animal populations, including species of conservation concern, such as the greater sage-grouse (Centrocercus urophasianus) (Knick et al. 2003). ...
Restoration planning requires a reliable seed supply, yet many projects occur in response to unplanned events. Identifying regions of greater disturbance risk could efficiently guide seed procurement. Using fire in U.S. Cold Deserts as an example, we demonstrate how historic disturbance can inform seed production choices. We compared differences in fire frequency, area burned, and percent of area burned among different management areas, identifying regions of particular need. We also present a case study focused on fire occurrence within important wildlife habitat, specifically looking at the greater sage‐grouse priority areas for conservation (PACs) within the Northern Basin and Range ecoregion. We used geospatial seed transfer zones as our focal management areas. We broadly considered generalized provisional seed transfer zones, created using climate and stratified by ecoregion, but also present results for empirical seed transfer zones, based on species‐specific research, as part of our case study. Historic fire occurrence was effective for prioritizing seed transfer zones: 23 of 132 provisional seed transfer zones burned every year, and, within each ecoregion, two provisional seed transfer zones comprised ≧50% of the total area burned across all years. Fire occurrence within PACs largely reflected the seed transfer zone priorities found for the ecoregion as a whole. Our results demonstrate that historic disturbance can be used to identify regions that encounter regular or large disturbance. This information can then be used to guide seed production, purchase, and storage, create more certainty for growers and managers, and ultimately increase restoration success.
