Human-induced changes in forest disturbance patterns have altered the successional patterns of aspen-conifer forests. These changes can lead to failure in aspen forest recruitment due to altered disturbance and ungulate herbivory regimes. Our objective was to characterize the temporal trends of aspen regeneration, recruitment, and ungulate browsing in stable aspen stands and to evaluate the impact of ungulate browsing on aspen, within the context of a large-scale aspen restoration program. From 2015-2022, mountain-wide restoration through prescribed burns and mechanical thinning of late-successional aspen-conifer stands treated 14,400 ha of the 28,700 ha of forest. During these broader restoration efforts, we monitored aspen stands and herbivory pressure at 60 nearby untreated sites. During the initial five-year survey period, chronically high levels of ungulate herbivory resulted in aspen recruitment failure. However, by 2023, native ungulate fecal counts had decreased by 66 % for elk and 50 % for deer, and ungulate meristem removal had dropped by more than 50 %. Aspen regeneration height and recruitment density increased by 20 cm and 88 %, reaching restoration targets. Secondly, we showed that topographic features and weather patterns mediated restoration success. Aspen increased at sites with greater snowpack and summer precipitation. Recruitment was more prevalent in southern locations, where elk fecal counts were lowest. Our findings suggest that ungulate herbivory can suppress aspen recruitment success and that weather, topography, and disturbance can mediate regeneration success. However, landscapescale restoration through prescribed disturbance likely promoted aspen regeneration indirectly by reducing ungulate herbivory in untreated stands.

North American deserts are changing due to expansion and increasing intensity of human activities. Disturbances and landscape change affect harvester ants, a keystone species in dryland ecosystems. Imagery acquired from small Unoccupied Aerial Vehicles (sUAVs) was analyzed to assess above-ground ant responses to change over time in the context of disturbance ecology and biological community interactions. We assessed the effectiveness of using sUAV imagery to detect spatiotemporal trends in ant disks over time and evaluated how ant disk density and area changed due to fire and rodent exclusion. In 2011, we implemented a controlled experiment in Tooele County, Utah, USA, to test the effects of experimental fire and rodent reduction on desert communities. We applied supervised object-based image classification to sUAV images from 2016, 2021, and 2023 and assessed classification accuracy and how fire and rodent removal affected ant disk density and area over time. Mapping accuracy of ant disk detection using sUAV imagery was consistent across all years. Our classification method detected ant disks at a lower density than manual methods. We failed to detect ant disks < 2.5 m in diameter; however, disks above 2.5 m were accurately identified. Burning increased disk density by 2.33 disks per plot, and rodent exclusion increased disk density by 1.73 disks per plot. Ant disk area increased by an average of 5.7 m2 per plot per year but was not affected by fire or rodents. sUAV imagery can be used to monitor harvester ants’ response to disturbances, with limitations. Our remote sensing methods have the potential to assess dryland ecosystem resilience to abiotic and biotic change by evaluating the responsiveness of harvester ant communities using mound and disk characteristics.

Changing wildfire regimes in recent decades have prompted extensive investigation into their hydrological impact. However, contradictory findings on post-fire flow regime changes have highlighted the complexity of this relationship. This study considers rich daily-resolution hydrological data on 898 burned catchments and over 8000 unburned control catchments to choose a set of 39 paired catchment experiments, along with 500 control pair experiments. We use these 500 control catchments to evaluate the extent to which the paired watershed approach accounts for hidden co-varying factors, finding that in most instances, it does not. We assess the influence of wildfires on flow magnitude, timing, and dynamicity. We also explore the effects of wildfire on water storage, evapotranspiration, and flood flows across the Western USA from 1984 to 2023. We find that percent changes in flow magnitude post-fire are not statistically significant and are uncorrelated with the percent of the catchment that burned, even when data are restricted to the critical first 5 years post-fire. However, linear regression analysis of 94 catchment variables found weak positive relationships between pre-fire forest cover and percent changes in flow magnitudes. Our results emphasize that the statistical uncertainty associated with even well-established methods may overshadow the magnitude of observed effects.

Herbivory influences plant evolution, the assembly of plant communities, and patterns of biological invasions. This study examined rodent herbivory patterns on the survival of native and non-native plant seedlings following fires in the Mojave Desert. We also assessed the extent of these effects on seedlings that use different life history strategies: grasses, forbs, and shrubs. Using a full-factorial design, we tested the individual and interactive effects of past fires and rodent exclusion on seedling survival. Five native and four non-native invasive plant species common in the Mojave Desert were grown to the seedling stage and placed in randomized order in the experimental plots. We assessed seedling survival after seven days. Survival was nearly two-fold greater for non-native seedlings (85

Human activities are increasing the occurrence of megafires that alter ecological dynamics in forest ecosystems. The objective of this study was to understand the impacts of a 610 km2 megafire on patterns of tree regeneration and herbivory across three forest types (aspen/fir, oak/maple, and pinyon/juniper). Seventeen transect pairs in adjacent burned/unburned forest stands (6 aspen/fir, 5 oak/maple, and 6 pinyon/juniper) were measured. Sapling density, meristem removal, and height were measured across the transect network over a three-year period from 2019 to 2021. Tree species able to resprout from surviving roots (oak and aspen) generally responded positively to fire while species that typically regenerate by seeding showed little post-fire regeneration. Browse pressure was concentrated on deciduous tree species and was greater in burned areas but the effect diminished over the three-year study period. Meristem removal by herbivores was below the critical threshold, resulting in vertical growth over time. Our results indicate that forest regeneration within the megafire scar was generally positive and experienced sustainable levels of ungulate browsing that were likely to result in forest recruitment success.

Abstract In North American deserts, the spread of invasive annual grasses is resulting in larger and more frequent fires that threaten the biological resilience and stability of desert ecosystems. Native consumers, including ants and rodents, likely have critical roles in defining post-fire plant community assembly and resilience to biological invasions. This study aimed to understand how western harvester ants (Pogonomyrmex occidentalis) that form mounds and large vegetation-free disks in the Great Basin Desert respond to fire and rodent community abundance. We tested this by installing treatment plots that excluded or allowed rodents and were burned or unburned in a full factorial design. We measured ant disk and mound size and density, along with a direct measure of ant activity in each experimental plot. Fire increased ant mound density by 126% compared to unburned plots. Rodent presence decreased ant activity by 39%, mound density by 59%, mound diameter by 13%, and mound height by 166%. We also show an interaction where the adverse effects of rodents on ants were greater in burned than in unburned plots. These results suggest that more frequent fires are likely to benefit ants, and fluctuations in rodent populations are likely to affect ant activity and disks and alter their responses to fire.

Consumers exert top-down controls on dryland ecosystem function, but recent increased fire activity may alter consumer communities and their interactions in post-fire environments. Native consumers, including ants and rodents, likely have critical roles in defining post-fire plant community assembly and resilience to biological invasions. This study aimed to understand how western harvester ants (Pogonomyrmex occidentalis) that form mounds and large vegetation-free disks in the Great Basin Desert respond to fire and rodent community abundance. We tested this by installing treatment plots that excluded or allowed rodents and were burned or unburned in a full factorial design. We measured ant disk and mound size and density, along with a direct measure of ant activity in each experimental plot. Fire increased ant mound density by 126% compared to unburned plots. Rodent presence decreased ant activity by 39%, mound density by 59%, mound diameter by 13%, and mound height by 166%. We also show an interaction where the adverse effects of rodents on ants were greater in burned than in unburned plots. These results suggest that more frequent fires are likely to benefit ants, and fluctuations in rodent populations are likely to affect ant activity and disks and alter their responses to fire.

Fire severity and herbivory by wild and domestic ungulates can strongly influence regeneration and recruitment of plant species. Importantly, the effects of herbivores on recruitment of plants is predicted to vary depending on the level of fire severity that an area experiences and habitat use of wild and domestic ungulates. In particular, two foundational plant species, quaking aspen (Populus tremuloides) and Gambel oak (Quercus gambelii), are widespread fire-adapted trees that support unique ecological communities; yet little is known about how fire severity and herbivory by ungulates potentially interact and shape their regeneration and recruitment. We studied aspen and Gambel oak regeneration and recruitment in relation to fire severity, topography, and habitat use by wild ungulates (elk and deer) and domestic livestock (cattle) across a forested region experiencing a large mixed-severity wildfire (10 years post fire). We predicted that plant regeneration and recruitment would increase with fire severity, but that recruitment would also be influenced by habitat use of ungulates. For aspen and Gambel oak, there was a strong positive relationship between regeneration and recruitment with fire severity. In addition, as the proportion of saplings that were browsed increased, plant recruitment decreased. However, the effects of herbivory on recruitment of resprouting trees in our study depended on the level of fire severity and habitat use of ungulates. Regeneration and recruitment of aspen and Gambel oak were greatest in areas experiencing moderate to high fire severity, and were absent or at low levels in areas that were unburned or experienced low fire severity (which would reduce availability of stems to be browsed). However, in higher fire severity areas there was variability in recruitment, depending on intensity of herbivore habitat use. Our study indicates that some fire-adapted plant species, such as aspen and Gambel oak, are most likely to recruit and promote the integrity and resilience of ecological communities in areas where (1) the positive effects of mixed-severity fire occur over sufficiently broad spatial extents and (2) the negative effects of herbivory by ungulates are reduced, especially in areas of lower fire severity, or where high-severity fires are smaller in size.

Consumers exert top-down controls on dryland ecosystem function, but recent increases in fire activity may alter consumer communities in post-fire environments. Native consumers, including ants and rodents, likely have critical roles in defining post-fire plant community assembly and resilience to biological invasions. This study aimed to understand how western harvester ants (Pogonomyrmex occidentalis) that form mounds and large vegetation-free disks that significantly influence plant community structure in the Great Basin Desert respond to fire and rodent community abundance. We tested this by installing treatment plots that excluded or allowed rodents and were burned or unburned in a full factorial design. We measured ant disk and mound size and density in each experimental plot. Fire increased ant mound density by 126% compared to unburned plots. Rodent presence decreased mound density by 59%, mound diameter by 13%, and mound height by 166%. We also show an interaction where the adverse effects of rodents on ant disk density were greater in burned than in unburned plots. The results suggest that booms in rodent populations are likely to have suppressive effects on ant mound and disk formation in native shrublands but that harvester ants may be released from rodent competition with the emergence of invasive grass-fire cycles.

The success of seeding projects in dryland systems is sporadic, with failure primarily driven by low seedling emergence and survival. This sporadic nature is influenced by a litany of biotic and abiotic factors that act in synergy to reduce recruitment success. These factors include erratic seasonal weather patterns, competition, predation, plant material selection, and restoration strategies. While some events are unpredictable and uncontrollable, others may be mitigated through thoughtful deliberation. Pathogenesis from soil- and seed-borne fungi is one form of predation that can decrease restoration success. Fungicide seed coatings are technologies used in the agriculture industry to mitigate fungal pathogens, yet these technologies are novel to wildland seeding. We evaluated the ability of a fungicide seed coating to improve bluebunch wheatgrass (Pseudoroegneria spicata) recruitment across a broad range of sites and determined how soil and climate affected seed treatments across six sites over 650 linear kilometers of sagebrush-steppe habitat in the Great Basin, United States. Treatment effects varied by site; however, on average, the fungicide treatment increased germination by 16%, emergence by 42%, and juvenile plant establishment by 60%. Fungicide seed treatments had a greater effect on seedling emergence in soils with lower pH, reduced wet-thermal accumulation during the winter, lower bulk density, and higher organic matter content. Most notably, the fungicide seed treatment resulted in higher plant establishment when emerged seedlings were exposed to longer periods of available soil moisture. Fungicide seed treatments can improve the establishment of native bunchgrasses, when soil and climate regimes are considered.

The concepts of resistance, recovery, and resilience are in diverse fields from behavioral psychology to planetary ecology. These “three Rs” describe some of the most important properties allowing complex systems to survive in dynamic environments. However, in many fields—including ecology—our ability to predict resistance, recovery and resilience remains limited. Here, we propose new disturbance terminology and describe a unifying definition of resistance, recovery, and resilience. We distinguish functional disturbances that affect short-term ecosystem processes from structural disturbances that alter the state factors of ecosystem development. We define resilience as the combination of resistance and recovery—i.e., the ability of a system to maintain its state by withstanding disturbance or rapidly recovering from it. In the Anthropocene, humans have become dominant drivers of many ecosystem processes and nearly all the state factors influencing ecosystem development. Consequently, the resilience of an individual ecological parameter is not an inherent attribute but a function of linkages with other biological, chemical, physical, and especially social parameters. Because every ecosystem experiences multiple, overlapping disturbances, a multidimensional resilience approach is needed that considers both ecosystem structure (configuration of linkages) and disturbance regime. We explore these concepts with a few case studies and recommend analytical tools and community-based approaches to strengthen ecosystem resilience. Disregarding cultural and social dimensions of disturbance regimes and ecosystem structures leads to undesirable outcomes, particularly in our current context of intensifying socioecological crises. Consequently, cultivating reciprocal relationships with natural disturbance regimes and ecosystem structures is crucial to Earth stewardship in the Anthropocene.

Human activities are increasing wildfires and livestock activity in arid ecosystems with potential implications for the spread of invasive grasses. The objective of this study was to test whether fire history and cattle activity alter soil resource gradients, thereby affecting patterns of Bromus rubens L. (red brome) invasion. Six paired burned and unburned transect lines (1-km long) were established in the northeast Mojave Desert along the boundaries of four independent wildfire scars. At 100-m transect increment points, we measured the distance to the two nearest cowpats, and two random points and measured the density, height, biomass, and seed production of red brome, soil moisture and inorganic nitrogen (N). Cattle activity was 29% greater along burned transects compared to unburned transects (P < 0.05). Red brome height, density, and seed production were 11-34% greater along burned transects than unburned transects (P < 0.05). Red brome height, biomass, density, and seed production were twofold to tenfold greater next to cowpats compared to random points (P < 0.05). Soils along burned transects and beneath cowpats had greater soil inorganic N (P < 0.05), which was positively correlated with red brome density, height, biomass, and seed production (R-2 = 0.60-0.85, P < 0.0001). Transgenerational effects were evident as seeds from red brome next to cowpats had 27% higher germination than seeds collected from random points. Positive responses of red brome to increased inorganic N related to fire and cattle activity may contribute fine fuel infill that drives invasive grass-fire cycles in deserts.

Climate change is likely to influence competitive interactions between native and non-native plant species by altering soil resource availability. The objective of this study was to characterize how shifts in fall precipitation timing due to climate change affect plant community assembly of native and non-native plant communities. We selected common non-native annuals and native perennial species from the Great Basin Desert in western North America and grew them in native, non-native, and native + non-native mixed communities. We tested the responses of these three community types to simulated earlier fall precipitation in a full factorial design. Early fall precipitation dramatically increased the height, density, biomass, seed production per unit biomass, and carbon-to-nitrogen ratio (C:N) of both native and non-native plant communities in comparison with the late precipitation treatment. However, competition with non-native species reduced the positive benefit of early precipitation for the native plant community. When grown in a native-only community, native plant species increased in height (twofold), density (threefold), biomass (13-fold), seed production per unit biomass (18-fold), and C:N (1.3-fold)but not tissue percent nitrogen as compared to a mixed community. In contrast, non-native plant species grown in mixed communities with natives showed little to no reduction in growth and reproduction. While all species benefitted from earlier fall precipitation our data suggest that increased earlier fall precipitation will likely magnify the exclusion of native vegetation by non-native annuals, particularly Bromus tectorum L. , which is largely responsible for human-grass-fire cycles in this ecoregion.

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.

Eastern Joshua tree ( Yucca jaegeriana ) plays a central role in the ecology of the Mojave Desert ecosystem. However, the emergence of invasive grass fire-cycles in the last several decades brings into question Joshua trees’ tolerance and resilience to changing fire regimes. This study’s objective was to examine the effects of wildfires on the structure and regeneration potential of Joshua trees forests. We examined the density, size class structure, and regeneration response of Joshua tree populations on a network of one kilometer transects along the boundaries of four independent wildfires and the interior of the largest fire that occurred 15 years ago (2005) in the northeast Mojave Desert. Burned edge and burned interior transects had 23- and 4.1-fold lower Joshua tree stand densities than unburned transects. The more robust recovery of stand density along burned interior transects compared to burned edge transects appears to be primarily driven by more prolific vegetative sprouting. Our data show that Joshua trees can sprout vegetatively following fire, but it is not a strong or consistent post-fire resprouter. Limiting the spread of invasive annual grasses and novel fire regimes will be critical to maintaining healthy Joshua tree populations into the future, particularly on the edge of its ecological range.

Many forest species are adapted to long-interval, high-severity fires, but the intervals between severe fires are decreasing with changes in climate, land use, and biological invasions. Although the effects of changing fire regimes on some important recovery processes have previously been considered, the consequences for the dispersal of propagules (plant seeds and fungal spores) in forest communities have not. We characterize three mechanisms by which changing fire regimes disrupt propagule dispersal in mesic temperate, boreal, and high-elevation forests: reduced abundance and altered spatial distributions of propagule source populations, less effective dispersal of propagules by wind, and altered behavior of animal dispersers and propagule predators. We consider how disruptions to propagule dispersal may interact with other factors that are also influenced by fire regime change, potentially increasing risk of forest conversion. Finally, we highlight urgent research topics regarding how dispersal limitation may shape twenty-first century forest recovery after stand-replacing fire.

Abstract Spatial interactions between trees influence forest community succession. The objective of this study was to investigate how shifts in forest composition and proximity between tree species affect stand development over time in mixed forest systems. At six locations across the Fishlake National Forest, Utah, USA, in stands where facilitation has been documented previously, tree‐ring samples were collected from aspen and subalpine fir trees. Basal area increment was calculated to characterize the effects of the proximity of overstory trees on multidecadal growth responses of aspen and subalpine fir in aspen‐dominant and mixed aspen–conifer stands. Subalpine fir seedlings were established next to aspen (within 10 cm) when aspen was between 15 and 120 years old with a mean age of 60 years. Aspen and subalpine fir growth rates were reduced with increasing conifer abundance. Aspen trees growing next to a proximate subalpine fir tree had slower growth rates over time than aspen trees growing independently. Growth rates of subalpine fir in aspen‐dominated stands were similar when growing independently or near aspen trees. However, subalpine fir in conifer‐dominated stands maintained higher growth rates when growing next to an aspen tree than when growing independently. The data suggest that as stand competition increases with conifer abundance, the proximity of overstory trees increases competitive exclusion of aspen while having a beneficial growth effect on subalpine fir. These results underscore the importance of maintaining natural fire regimes in forest systems that keep competitive interactions in balance.

Climate forecasts and disturbance mapping increasingly inform strategies for ecological restoration practices. Our study objectives were to understand how a postfire rehabilitation seed mix responds to fire, seeding timing, and changes in fall precipitation timing due to climate change. We planted seeds commonly used in the Great Basin Desert of North America on soil cores in a randomized block design. We imposed two experimental treatments, experimental fire (burned seedbeds or unburned seedbeds) and timing of seeding with simulated precipitation (early September vs. mid‐October) in a two‐way factorial design. We measured seedling emergence (1 month posttreatment), plant density, biomass, and seed production. Early seeding and precipitation reduced seedling emergence over 2‐fold but increased total plant density (3‐fold), biomass (13‐fold), and seed production (140‐fold) compared to delayed seeding and precipitation applications. Antelope bitterbrush was the only species with a negative response to early seeding and precipitation, with a decrease in both density and biomass (over 2‐fold) by the end of the study. Burned seedbeds overall had little effect on measured outcomes for the total plant community. Burned seedbeds decreased forb seedling emergence 2‐fold and alfalfa and Lewis blue flax density almost 3‐fold but increased overall forb seed production 7‐fold while other species and functional groups had minimal responses. Earlier seeding and precipitation interacted with the effects of burned seedbeds to increase biomass of Wyoming big sagebrush and western yarrow. The positive response of species to earlier fall seeding and precipitation underscores the importance of adapting our restoration practices for changing climate conditions.