Greater Yellowstone Ecosystem Research Articles

Drivers of forest change in the Greater Yellowstone Ecosystem

AbstractQuestionsGlobal climate change is predicted to cause widespread shifts in the distribution and composition of forests, particularly in mountain environments where climate exerts strong controls on tree community arrangement. The upslope movement of vegetation has been observed in association with warming temperatures and is especially evident in ecotones—the transition zones between vegetation types. We explored the role of drought and tree mortality on recent changes in high‐elevation forests.LocationGreater Yellowstone Ecosystem, USA.MethodsWe established 19 forest demography plots along an elevational gradient spanning dominant high‐elevation vegetation types.ResultsTree establishment dates indicated the upslope movement of Pinus albicaulis (whitebark pine) treeline and ecotone shift from meadow to forest starting in the 1950s. An expansion of the growing season likely contributed to the upward expansion of the treeline. Comparisons between overstory and understory tree composition suggested ongoing succession in the absence of fire at lower elevations, namely the replacement of Pinus contorta (lodgepole pine) by Abies lasiocarpa (subalpine fir). P. contorta seedlings were distributed at higher elevations than overstory trees of the same species, suggesting some potential for upslope movement with warming conditions; P. albicaulis seedlings, conversely, were distributed throughout all elevations of the transect. Significant tree mortality occurred in Pinus spp. and disproportionately affected P. albicaulis, as a result of a regional Dendroctonus ponderosae (mountain pine beetle) outbreak (2008–2012). Mortality events were strongly associated with drier than average conditions 2–3 years prior to tree death.ConclusionRising sensitivity to arid conditions in the mid‐20th century amid already dense, aging forests appears to have increased susceptibility to beetle‐induced mortality during the most recent drought. Tree species in the study area responded individually to global change stressors, which acted on these forests in complex ways and led to both ecotone shifts and stability. This work highlights the interplay between succession, forest disturbances and climate‐related growth responses in driving forest compositional change in subalpine and treeline environments.

Spaceborne LiDAR and animal-environment relationships: An assessment for forest carnivores and their prey in the Greater Yellowstone Ecosystem

Animal conservation requires understanding animal-habitat relationships. The integration of novel remote sensing platforms such as Light Detection and Ranging (LiDAR) technology has dramatically improved the resolution of insight when evaluating animal-habitat relationships by characterizing forest structure. However, conventional LiDAR collection (e.g., airborne or terrestrial laser scanning) may be limited by small spatial extents and logistical constraints (e.g., budget) associated with sampling. NASA’s Global Ecosystem Dynamics Investigation (GEDI) mission provides an alternative and complement to conventional LiDAR sampling with globally available waveform LiDAR, which is being collected to characterize vertical and horizontal structure of Earth’s forests. Forest carnivores are wide-ranging species occupying forested ecosystems, and are generally associated with vertical and horizontal forest structure for their survival and reproduction. We evaluated patterns in occurrence and habitat use of forest carnivores, which included Pacific martens (Martes caurina), Rocky Mountain red foxes (Vulpes vulpes macroura), and coyotes (Canis latrans) and patterns in occurrence of their prey; American red squirrels (Tamiasciurus hudsonicus) and snowshoe hares (Lepus americanus). Camera trap data were collected during the 2014–2017 winters in the Greater Yellowstone Ecosystem in Wyoming, USA. Our objectives were to (1) combine GEDI samples with multispectral satellite imagery from Landsat 8 to upscale vertical forest structure metrics; (2) assess the relative importance of environmental characteristics influencing occurrence and habitat use of forest-associated predators and prey; and (3) determine if GEDI-derived variables aided our efforts in characterizing animal-environment relationships. We used Random Forest regression models to upscale GEDI samples across our study area and implemented a multi-tiered approach using generalized linear mixed effect models to simultaneously evaluate animal-environment relationships and how GEDI-derived metrics improved the animal-habitat models. GEDI-derived metrics of relative height and foliage height diversity improved our animal-environment models and were among the strongest covariates (effect sizes were 1.3–1.8 times larger than the next closest) in the coyote, red squirrel, and snowshoe hare models. All five species were influenced to some degree by the frequency of rebaiting a camera trap and varying conditions of snow depth. Collectively, our work indicates forest canopy height and complexity variables significantly improved our ability to assess the importance of forest characteristics on forest carnivores and their prey. Indeed, there is an untapped opportunity to enhance animal ecology and conservation planning with continued integration of GEDI information with freely available satellite data to characterize attributes of forest structure across expansive areas.

Competitive release during fire succession influences ecological turnover in a small mammal community.

Ecologists have long debated the relative importance of biotic interactions versus species-specific habitat preferences in shaping patterns of ecological dominance. In western North America, cycles of fire disturbance are marked by transitions between North American deermice (Peromyscus maniculatus), which predominate after wildfires, and southern red-backed voles (Myodes gapperi), which gradually replace deermice 3-4 years postfire and maintain dominance as forests mature. While this shift has been frequently documented, the processes that mediate this turnover are debated. One possibility is competitive release, which predicts a reduction in vole competition may contribute to niche expansion and population growth in deermice. Alternatively, turnover in both species may be shaped by differences in their preferred habitat and resource base, as predicted by optimum foraging theory. We evaluate these hypotheses using stable isotopes and spatial mark-recapture of deermouse and vole populations sampled prior to and following a fire as part of a longitudinal study in the Greater Yellowstone Ecosystem. Fire disturbance was associated with a 94% decrease in vole abundance but a 102% increase in deermice. Even after accounting for microhabitat, vole and deermouse populations were negatively correlated spatially and temporally (R=-0.45), and competitor abundance was more important prefire than postfire. When vole abundance was high (prefire), vole dietary niche space was seven times broader than that of deermice. Postfire, deermouse dietary niche nearly tripled and was enriched in 13 C (i.e., more C4 plants), while voles occupied a slightly reduced dietary niche (79% of prefire breadth). Our results suggest deermice are experiencing ecological release due to a reduction in vole competition but vole shifts are largely driven by habitat preferences.

Flowering time advances since the 1970s in a sagebrush steppe community: Implications for management and restoration.

Climate change is widely known to affect plant phenology, but little is known about how these impacts manifest in the widespread sagebrush ecosystem of the Western United States, which supports a number of wildlife species of concern. Shifts in plant phenology can trigger consequences for the plants themselves as well as the communities of consumers that depend upon them. We assembled historical observations of first-flowering dates for 51 species collected in the 1970s and 1980s in a montane sagebrush community in the Greater Yellowstone Ecosystem and compared these to contemporary phenological observations targeting the same species and locations (2016-2019). We also assembled regional climate data (average spring temperature, day of spring snowmelt, and growing degree days) and tested the relationship between first-flowering time and these variables for each species. We observed the largest change in phenology in early-spring flowers, which, as a group, bloomed on average 17 days earlier, and as much as 36 days earlier, in the contemporary data set. Mid-summer flowers bloomed on average 10 days earlier, nonnative species 15 days earlier, and berry-producing shrubs 5 days earlier, while late summer flowering plants did not shift. The greatest correlates of early-spring and mid-summer flowering were average spring temperature and day of snowmelt, which was 21 days earlier, on average, in 2016-2019 relative to the 1973-1978 observations. The shifts in flowering phenology that we observed could indicate developing asynchronies or novel synchronies of these plant resources and wildlife species of conservation concern, including Greater Sage-grouse, whose nesting success is tied to availability of spring forbs; grizzly bears, which rely heavily on berries for their fall diet; and pollinators. This underscores the importance of maintaining a diverse portfolio of native plants in terms of species composition, genetics, phenological responsiveness to climatic cues, and ecological importance to key wildlife and pollinator species. Redundancy within ecological niches may also be important considering that species roles in the community may shift as climate change affects them differently. These considerations are particularly relevant to restoration and habitat-enhancement projects in sagebrush communities across western North America.

Exploring durophagy among modern gray wolves from the Greater Yellowstone Ecosystem with dental microwear texture analysis

Gray wolf (Canis lupus) dietary behavior can be highly variable; prey species for wolves span a range of ungulates to the consumption of smaller animals. While prey species for wolves are well documented, carcass utilization within and between wolf populations is less understood. This paper examines a modern population of wolves from the Greater Yellowstone Ecosystem (GYE) with dental microwear texture analysis (DMTA) to gauge utilization of bone resources, or durophagy, across biological, physical, social, geographical, and temporal variables. Results indicate gradation in durophagous behavior among GYE wolves does not correlate with sex, intra-population body size (as inferred from skeletal and soft tissue measurements), pack association, or age class. Together, findings suggest that feeding ecologies for wolves are not specific to these factors. We also found that antemortem tooth breakage rates are not positively correlated with dental microwear textures that infer durophagy. We further compare dental microwear measures with previously published data from Alaskan wolves, who were collected decades before the GYE wolf sample. Results imply elevated carcass exploitation in the contemporary GYE wolf population sample. If minimal inter-population differences are assumed, data presented here show dietary behaviors of North American gray wolves have changed over the past fifty years, indicating a possible long-term trend that may be linked to decreased winter severity and climate change.

The role of monitoring and research in the Greater Yellowstone Ecosystem in framing our understanding of the effects of disease on amphibians

Emerging infectious disease threatens amphibian biodiversity worldwide, including in landscapes that are protected from many anthropogenic stressors. We summarized data from studies in the Greater Yellowstone Ecosystem (GYE), one of the largest and most complete temperate-zone ecosystems on Earth, to assess the current state of knowledge about ranaviruses and the novel amphibian chytrid fungus (Bd) in this landscape, and to provide insight into future threats and conservation strategies. Our comprehension of these amphibian diseases in the GYE is based on >20 years of monitoring, surveys, population studies, and opportunistic observations of mortality events. Research indicates that local species are affected differently, depending on temperature, community structure, and location in the GYE. Bd has not been linked to die-offs in the GYE but evidence for ongoing reductions in survival contributes to foundational data about the effects of this pathogen in North America. Localized mortality events attributed to, or consistent with, disease from ranaviruses, are widespread in the GYE, but there is less information on how ranaviruses affect amphibian vital rates. The significance of disease in the long-term persistence of amphibians in the GYE is linked to anticipated changes in climate, especially drought. Additionally, expected increases in visitor use, and its associated impacts, have the potential to exacerbate the effects of disease. Long-term information from this large, intact landscape helps to frame our understanding of the effects of disease on amphibians and provides data that can contribute to management decisions, mitigation strategies, and forecasting efforts.

Examination of the interaction between age-specific predation and chronic disease in the Greater Yellowstone Ecosystem.

Predators may create healthier prey populations by selectively removing diseased individuals. Predators typically prefer some ages of prey over others, which may, or may not, align with those prey ages that are most likely to be diseased. The interaction of age-specific infection and predation has not been previously explored and likely has sizable effects on disease dynamics. We hypothesize that predator cleansing effects will be greater when the disease and predation occur in the same prey age groups. We examine the predator cleansing effect using a model where both vulnerability to predators and pathogen prevalence vary with age. We tailor this model to chronic wasting disease (CWD) in mule deer and elk populations in the Greater Yellowstone Ecosystem, with empirical data from Yellowstone grey wolves and cougars. Model results suggest that under moderate, yet realistic, predation pressure from cougars and wolves independently, predators may decrease CWD outbreak size substantially and delay the accumulation of symptomatic deer and elk. The magnitude of this effect is driven by the ability of predators to selectively remove late-stage CWD infections that are likely the most responsible for transmission, but this may not be the age class they typically select. Thus, predators that select for infected young adults over uninfected juveniles have a stronger cleansing effect, and these effects are strengthened when transmission rates increase with increasing prey morbidity. There are also trade-offs from a management perspective-that is, increasing predator kill rates can result in opposing forces on prey abundance and CWD prevalence. Our modelling exploration shows that predators have the potential to reduce prevalence in prey populations when prey age and disease severity are considered, yet the strength of this effect is influenced by predators' selection for demography or body condition. Current CWD management focuses on increasing cervid hunting as the primary management tool, and our results suggest predators may also be a useful tool under certain conditions, but not necessarily without additional impacts on host abundance and demography. Protected areas with predator populations will play a large role in informing the debate over predator impacts on disease.

Co-Occurring Wyoming Pinus Species Exhibit Differing Climate–Growth Relationships

The North American Dendroecological Field week (NADEF) is an intensive dendrochronology workshop, funded in part by the National Science Foundation. The 2019 Introductory Group at NADEF developed two precisely dated tree-ring width chronologies for Pinus contorta (lodgepole pine) and Pinus flexilis (limber pine) at the Wolf Knob site ca. 5 km west of Beartooth Lake, WY, within the bounds of the Shoshone National Forest (SNF), in the Greater Yellowstone Ecosystem (GYE). Wolf Knob is a semi-arid, S- to SW-facing, mid- to high-elevation site, making it an ideal location to examine the climate sensitivity of annual tree-ring width increments. Here, we show that two co-located Pinus species exhibit differing climate–growth relationships, with P. contorta exhibiting relatively weak correlations with precipitation (r = 0.37; p < 0.01) and temperature (r = –0.23; p < 0.05) during the late summer, and P. flexilis exhibiting stronger overall correlations with both cool-season (r = 0.48; p < 0.01) and warm-season precipitation (r = 0.51; p < 0.01) as well as with snowpack records (r = 0.45; p < 0.05). Our results suggest these two Pinus species may face disparate threats in the face of regional climate change, with P. flexilis being particularly vulnerable to drought conditions and declining snowpacks in the GYE. The differing seasonal climate sensitivities of the two species is likely caused by microsite conditions (e.g. soil moisture capacity, incoming solar radiation) and distinct species-climate responses, underscoring the importance of not only site selection, but also microsite and individual selection in dendroclimatological sampling. Finally, this work contributes to identifying Snow Water Equivalent (SWE)-sensitive tree-ring proxies in the GYE, critical for understanding ongoing warming-induced snowpack declines across western North America, particularly given the projections of a largely snow-free (April 1) GYE by 2075.

Spaceborne Lidar and Animal-Environment Relationships: An Assessment for Forest Carnivores and Their Prey in the Greater Yellowstone Ecosystem

Spaceborne Lidar and Animal-Environment Relationships: An Assessment for Forest Carnivores and Their Prey in the Greater Yellowstone Ecosystem

Grizzlies, Wolves, and Law in the Greater Yellowstone Ecosystem: Wildlife Management Amidst Jusidictional Complexity and Tension

Grizzlies, Wolves, and Law in the Greater Yellowstone Ecosystem: Wildlife Management Amidst Jusidictional Complexity and Tension

Multi-proxy record of Holocene paleoenvironmental conditions from Yellowstone Lake, Wyoming, USA

A composite 11.82 m-long (9876–-67 cal yr BP) sediment record from Yellowstone Lake, Wyoming was analyzed using a robust set of biological and geochemical proxies to investigate the paleoenvironmental evolution of the lake and its catchment in response to long-term climate forcing. Oxygen isotopes from diatom frustules were analyzed to reconstruct Holocene climate changes, and pollen, charcoal, diatom assemblages, and biogenic silica provided information on terrestrial and limnological responses. The long-term trends recorded in the terrestrial and limnic ecosystems over the last 9800 years reflect the influence of changes in the amplification of the seasonal cycle of insolation on regional climate. The early Holocene (9880–6700 cal yr BP) summer insolation maximum and strengthening of the northeastern Pacific subtropical high-pressure system created warm dry conditions and decreasing summer insolation in the middle (6700–3000 cal yr BP) and late (3000–-67 cal yr BP) Holocene resulted in progressively cooler, wetter conditions. Submillenial climate variation is also apparent, with a wetter/cooler interval between 7000 and 6800 cal yr BP and warmer and/or drier conditions from 4500 to 3000 cal yr BP and at ca. 1100 cal yr BP. These data show that the Yellowstone Lake basin had a climate history typical of a summer-dry region, which helps to better define the spatial variability of Holocene climate in the Greater Yellowstone Ecosystem.

The magnitude, direction, and tempo of forest change in Greater Yellowstone in a warmer world with more fire

AbstractAs temperatures continue rising, the direction, magnitude, and tempo of change in disturbance‐prone forests remain unresolved. Even forests long resilient to stand‐replacing fire face uncertain futures, and efforts to project changes in forest structure and composition are sorely needed to anticipate future forest trajectories. We simulated fire (incorporating fuels feedbacks) and forest dynamics on five landscapes spanning the Greater Yellowstone Ecosystem (GYE) to ask the following questions: (1) How and where are forest landscapes likely to change with 21st‐century warming and fire activity? (2) Are future forest changes gradual or abrupt, and do forest attributes change synchronously or sequentially? (3) Can forest declines be averted by mid‐21st‐century stabilization of atmospheric greenhouse gas (GHG) concentrations? We used the spatially explicit individual‐based forest model iLand to track multiple attributes (forest extent, stand age, tree density, basal area, aboveground carbon stocks, dominant forest types, species occupancy) through 2100 for six climate scenarios. Hot‐dry climate scenarios led to more fire, but stand‐replacing fire peaked in mid‐century and then declined even as annual area burned continued to rise. Where forest cover persisted, previously dense forests were converted to sparse young woodlands. Increased aridity and fire drove a ratchet of successive abrupt declines (i.e., multiple annual landscape‐level changes ≥20%) in tree density, basal area, and extent of older (&gt;150 yr) forests, whereas declines in carbon stocks and mean stand age were always gradual. Forest changes were asynchronous across landscapes, but declines in stand structure always preceded reductions in forest extent and carbon stocks. Forest decline was most likely in less topographically complex landscapes dominated by fire‐sensitive tree species (Picea engelmannii, Abies lasiocarpa, Pinus contorta var. latifolia) and where fire resisters (Pseudotsuga menziesii var. glauca) were not already prevalent. If current GHG emissions continue unabated (RCP 8.5) and aridity increases, a suite of forest changes would transform the GYE, with cascading effects on biodiversity and myriad ecosystem services. However, stabilizing GHG concentrations by mid‐century (RCP 4.5) would slow the ratchet, moderating fire activity and dampening the magnitude and rate of forest change. Monitoring changes in forest structure may serve as an operational early warning indicator of impending forest decline.

Evaluating the importance of wolverine habitat predictors using a machine learning method

Abstract In the conterminous United States, wolverines (Gulo gulo) occupy semi-isolated patches of subalpine habitats at naturally low densities. Determining how to model wolverine habitat, particularly across multiple scales, can contribute greatly to wolverine conservation efforts. We used the machine-learning algorithm random forest to determine how a novel analysis approach compared to the existing literature for future wolverine conservation efforts. We also determined how well a small suite of variables explained wolverine habitat use patterns at the second- and third-order selection scale by sex. We found that the importance of habitat covariates differed slightly by sex and selection scales. Snow water equivalent, distance to high-elevation talus, and latitude-adjusted elevation were the driving selective forces for wolverines across the Greater Yellowstone Ecosystem at both selection orders but performed better at the second order. Overall, our results indicate that wolverine habitat selection is, in large part, broadly explained by high-elevation structural features, and this confirms existing data. Our results suggest that for third-order analyses, additional fine-scale habitat data are necessary.

Scavengers reduce potential brucellosis transmission risk in the Greater Yellowstone Ecosystem

AbstractScavengers likely play an important role in ecosystem energy flow as well as disease transmission, but whether they facilitate or reduce disease transmission is often unknown. In the Greater Yellowstone Ecosystem, scavengers are likely to reduce the transmission and subsequent spread of brucellosis within and between livestock and elk by consuming infectious abortion materials, thereby removing the infectious agent from the landscape. We used remote cameras to monitor the time to removal of simulated abortion materials by scavengers at 264 sites from February to June in 2017 and 2018 and assessed the effects of habitat and land management on time to removal in southwest Montana. Time to removal of fetal materials decreased in grassland habitats ( = 2.9 d, credible interval = [1.8–5.0]) in comparison to sagebrush habitats ( = 5.4 d [3.4–9.3]) and forest habitats ( = 5.2 d [3.3–9.0]). In addition, there was an 88% probability that time to removal of fetal materials was slower at sites where mammalian scavengers were actively reduced ( = 6.5 d [3.4–12.8]) compared to sites with no scavenger reduction ( = 4.1 d [2.3–7.8]). Our research indicates that if elk and livestock are commingling during the brucellosis risk period, there is a 90% probability that abortion materials will be removed by scavengers within 16 d across all sites. Coyotes, red foxes, golden and bald eagles, Corvus spp., and turkey vultures were the dominant scavengers, removing 90% of the fetal materials. Actions to maintain the breadth and diversity of scavengers on the landscape are potential management options that could reduce disease transmission risk to livestock in a system where the wildlife reservoir is difficult to address.

Fine-Scale NDVI Reconstruction Back to 1906 from Tree-Rings in the Greater Yellowstone Ecosystem

Global warming and related disturbances, such as drought, water, and heat stress, are causing forest decline resulting in regime shifts. Conventional studies have combined tree-ring width (TRW) and the normalized difference vegetation index (NDVI) to reconstruct NDVI values and ignored the influences of mixed land covers. We built an integrated TRW-NDVI model and reconstructed the annual NDVI maps by using 622 Landsat satellite images and tree cores from 15 plots using point-by-point regression. Our model performed well in the study area, as demonstrated by significant reconstructions for 71.14% (p &lt; 0.05) of the area with the exclusion of water and barren areas. The error rate between the reconstructed NDVI using the conventional approach and our approach could reach 10.36%. The 30 m resolution reconstructed NDVI images in the recent 100 years clearly displayed a decrease in vegetation density and detected decades-long regime shifts from 1906 to 2015. Our study site experienced five regime shifts, markedly the 1930s and 1950s, which were megadroughts across North America. With fine resolution maps, regime shifts could be observed annually at the centennial scale. They can also be used to understand how the Yellowstone ecosystem has gradually changed with its ecological legacies in the last century.

Amphibian population responses to mitigation: Relative importance of wetland age and design

Wetland creation is a common practice to mitigate for the loss of natural wetlands. However, there is still uncertainty about how effectively created wetlands replace habitat provided by natural wetlands. This uncertainty is due in part because post-construction monitoring of biological communities, and vertebrates especially, is rare and typically short-term (<5 years). We estimated occupancy of 4 amphibian species in 8 created mitigation wetlands, 7 impacted wetlands, and 7 reference wetlands in the Greater Yellowstone Ecosystem in Wyoming, USA. Mitigation wetlands were created to replace wetland habitat that was lost during road construction and ranged in age from 1 to 10 years when sampled. Impacted wetlands were natural wetlands partially filled by road construction and were adjacent to a highway. We sampled for amphibian larvae during 6 summers from 2013 to 2020 and used multi-species occupancy models that estimated detection and occupancy of each of 4 amphibian species to determine how amphibian responses changed over time, especially in mitigation wetlands. Occupancy did not differ between impacted and reference wetlands for any of the 4 amphibian species. Western Toads (Anaxyrus boreas) were most common (although briefly) in created wetlands, and occupancy of Columbia Spotted Frogs (Rana luteiventris), Western Tiger Salamanders (Ambystoma mavortium), and Boreal Chorus Frogs (Pseudacris maculata) was lower in created wetlands than in impacted or reference wetlands. Individual wetland area was positively associated with occupancy for all 4 species and wetland vegetation cover was positively associated with Boreal Chorus Frog and Columbia Spotted Frog occupancy; these results emphasize the importance of design characteristics when planning mitigation wetlands. The link between wetland age and occupancy was complex and included threshold and quadratic relationships for three of the four species, but only Boreal Chorus Frog occupancy was still increasing slowly at the end of our study. Our results indicate created wetlands did not attain the suitability of impacted and natural wetlands for local amphibians, even several years after construction. The complex relationships between wetland age and species-specific occupancy illustrate the importance of long-term monitoring in describing population responses to the construction of wetlands as mitigation for wetland loss.

Agent-Based Models for Collective Animal Movement: Proximity-Induced State Switching

Animal movement is a complex phenomenon where individual movement patterns can be influenced by a variety of factors including the animal’s current activity, available terrain and habitat, and locations of other animals. Motivated by modeling grizzly bear movement in the Greater Yellowstone Ecosystem, this article presents an agent-based model represented in a state-space framework for collective animal movement. The novel contribution of this work is a collective animal movement model that captures interactions between animals that can trigger changes in movement patterns, such as when a dominant grizzly bear may cause another subordinate bear to temporarily leave an area. The modeling framework enables learning different movement patterns through a state-space representation with particle-MCMC methods for fully Bayesian model fitting and the prediction of future animal movement behaviors.Supplementary materials accompanying this paper appear online.

Widespread regeneration failure in forests of Greater Yellowstone under scenarios of future climate and fire.

Changing climate and disturbance regimes are increasingly challenging the resilience of forest ecosystems around the globe. A powerful indicator for the loss of resilience is regeneration failure, that is, the inability of the prevailing tree species to regenerate after disturbance. Regeneration failure can result from the interplay among disturbance changes (e.g., larger and more frequent fires), altered climate conditions (e.g., increased drought), and functional traits (e.g., method of seed dispersal). This complexity makes projections of regeneration failure challenging. Here we applied a novel simulation approach assimilating data-driven fire projections with vegetation responses from process modeling by means of deep neural networks. We (i) quantified the future probability of regeneration failure; (ii) identified spatial hotspots of regeneration failure; and (iii) assessed how current forest types differ in their ability to regenerate under future climate and fire. We focused on the Greater Yellowstone Ecosystem (2.9×106 ha of forest) in the Rocky Mountains of the USA, which has experienced large wildfires in the past and is expected to undergo drastic changes in climate and fire in the future. We simulated four climate scenarios until 2100 at a fine spatial grain (100m). Both wildfire activity and unstocked forest area increased substantially throughout the 21st century in all simulated scenarios. By 2100, between 28% and 59% of the forested area failed to regenerate, indicating considerable loss of resilience. Areas disproportionally at risk occurred where fires are not constrained by topography and in valleys aligned with predominant winds. High-elevation forest types not adapted to fire (i.e., Picea engelmannii-Abies lasiocarpa as well as non-serotinous Pinus contorta var. latifolia forests) were especially vulnerable to regeneration failure. We conclude that changing climate and fire could exceed the resilience of forests in a substantial portion of Greater Yellowstone, with profound implications for carbon, biodiversity, and recreation.

Post‐fire conifer regeneration hinders digital estimation of understorey plant cover in subalpine forest vegetation

AbstractQuestion: Reliable estimates of understorey (non‐tree) plant cover following fire are essential to assess early forest community recovery. Photographic digital image analysis (DIA) is frequently used in seral, single‐strata vegetation, given its greater objectivity and repeatability compared to observer visual estimation; however, its efficacy in multi‐strata forest vegetation may be compromised, where various visual obstructions (coarse downed wood [CDW], conifer regeneration, and shadows) may conceal plant cover in the digital imagery. We asked whether vegetation complexity influences plant cover estimated by DIA relative to two visual methods: plot‐level (20 m2) estimation (PLE) and quadrat‐level (1 m2) estimation (QLE)?Location: Greater Yellowstone Ecosystem, USA.Methods: We estimated understorey plant cover in subalpine forest vegetation on permanent plots (n = 141) at two study areas ~30 years after the 1988 Yellowstone fires to: (a) assess differences in visual obstructions between study areas in our digital imagery; (b) compare digital to visual estimates of plant cover; and (c) determine relationships between estimated plant cover and visual obstructions measured in situ.Results: Percent conifer regeneration pixels differed significantly (odds ratio = 8.34) between study areas which represented the greatest difference in visual obstructions. At the study area with lower conifer pixels, DIA estimated 9% (95% confidence interval [CI] = 3%–14%) and 16% (95% CI = 10%–21%) more understorey plant cover than PLE or QLE, respectively, but had comparable variability. At the study area with higher conifer pixels, DIA estimated 28% (95% CI = 24%–32%) and 22% (95% CI = 18%–26%) less understorey plant cover than PLE or QLE, respectively, and had more variability. Furthermore, plot‐level subcanopy regeneration (height&gt;137 cm) density was negatively associated with digitally derived plant cover but showed no relationship with visually derived plant cover.Conclusions: Post‐fire conifer regeneration hindered the efficacy of DIA in estimating understorey plant cover. Digital estimation is advantageous in single‐strata vegetation but should not be used in complex, multi‐strata vegetation.

Spatial and temporal variability in summer diet of gray wolves (Canis lupus) in the Greater Yellowstone Ecosystem.

The role of predation by large carnivores in suppressing prey populations and structuring ecosystems is highly debated, calling for a detailed understanding of carnivore diets. Wolves (Canis lupus) roam across three continents and persist throughout widely different ecosystems. Their diet is flexible and may vary spatially as well as seasonally, which requires analysis of diet on different spatial and temporal scales. Few studies have investigated the summer diet of wolves, which is more variable, consists of smaller prey, and requires different methods than studying their winter diet. To better understand the summer diet of wolves, we combined three independently collected wolf scat data sets from three distinctly different portions of the Greater Yellowstone Ecosystem: Yellowstone National Park (2009), Grand Teton National Park (2003 – 2009), and the Absaroka-Beartooth Wilderness (2009 – 2010). These areas represent different ecological conditions and management regimes, which may impact wolf diet. We estimated relative biomass and compared occurrence of different prey species among packs, years, as well as the three regions. In total, we analyzed 1,906 wolf scats and found that neonate cervids, adult elk, and adult deer were the most important prey species in the summer diet of the wolves. We found dietary variation among packs residing in the same area, as well as across years. The occurrence of neonate cervids displayed the most variation, and low occurrence of this prey type often was associated with a more diverse diet. Wolf packs within the national parks had a higher occurrence of medium-sized prey (~ 50 – 70 kg) and lower occurrence of small-sized prey (≤ 20 kg) compared to wolves in the Absaroka-Beartooth Wilderness. These results demonstrate flexibility in summer diet across packs, years, and between regions within the Greater Yellowstone Ecosystem.