Northern Arizona University

Quaking aspen (Populus tremuloides Michx.) ecosystems are highly valued in the southwestern United States because of the ecological, economic, and aesthetic benefits they provide. Aspen has experienced extensive mortality in recent decades, and there is evidence that many areas in Arizona, United States lack adequate recruitment to replace dying overstory trees. Maintaining sustainable levels of regeneration and recruitment (i.e. juveniles) is critical for promoting aspen ecosystem resilience and adaptive capacity, but questions remain about which factors currently limit juvenile aspen and which strategies are appropriate for managing aspen in an increasingly uncertain future. To fill these critical knowledge gaps, we sampled aspen populations across Arizona and collected data representing a suite of biotic and abiotic factors that potentially influence juvenile aspen. Specifically, we addressed two questions: (i) Is aspen sustainably regenerating and recruiting in Arizona? and (2) Which biotic and abiotic factors significantly influence aspen regeneration and recruitment? We found that many aspen populations in Arizona lack sustainable levels of juvenile aspen, and the status of recruitment was especially dire, with 40% of study plots lacking a single recruiting stem. Aspen regeneration was less abundant on warmer sites than cooler ones, highlighting the threat that a rapidly warming climate poses to aspen sustainability. Aspen recruitment was significantly more abundant in areas with recent fire than in areas without fire, and recruitment had a strong positive relationship with fire severity. The most important limiting factors for aspen recruitment were ungulate browse, especially by introduced Rocky Mountain elk (Cervus canadensis nelsoni), and the invasive insect, oystershell scale (Lepidosaphes ulmi). We conclude with a discussion of how management can promote sustainability of aspen populations by addressing the array of threats that aspen faces, such as a warming climate, chronic ungulate browse, and outbreaks of oystershell scale.

Peer review is a critical evaluation process, one that is time‐consuming but needed to maintain quality and credibility in science. At JGR Biogeosciences we are honoring the many 2024 reviewers who donated their time and expertise to ensure rigor, novelty, inclusiveness, and open practices for improving and advancing biogeosciences research.

The impact of killing in combat (KIC) on veterans’ long-term psychological health is multifaceted and influenced by deployment contexts. This study compared two samples of Norwegian veterans from combat-oriented (Afghanistan 2001–2011, N = 4,053) and peacekeeping (Lebanon 1978–1998, N = 10,605) missions to examine how personal threats, witnessing death/injury, and KIC uniquely predicted long-term mental health, alcohol use, and quality of life (QoL). In the combat-oriented sample, personal threats and witnessing death/injury predicted negative outcomes, while KIC did not. Among peacekeepers, personal threats, witnessing death/injury, and KIC independently predicted posttraumatic stress disorder (PTSD), depression, anxiety, alcohol use, insomnia, and lower QoL. These findings reveal diverging effects of KIC on veterans from combat-oriented and peacekeeping missions, respectively, suggesting that the impact of potentially morally injurious events like KIC is shaped by mission-specific contextual factors.

Missouri River streamflow increased substantially during the 20th century, with multiple large floods occurring since 1990. Using land surface models and water budget simulations, we examined the extent to which increased flow was driven by natural climate variability, anthropogenic climate trends, land‐use and land‐cover change (LULCC), and ecological effects of elevated atmospheric CO2. Natural climate variability (arising largely from coupled ocean‐atmosphere circulation systems in both the Pacific and North Atlantic) accounted for ∼765 m³ s⁻¹ of the ∼900 m³ s⁻¹ increase in flow since mid‐century, while anthropogenic climate trends negatively forced flow by increasing evapotranspiration more than precipitation. LULCC and elevated CO2 further increased simulated mean streamflow by ∼550 and ∼70 m³ s⁻¹, respectively, relative to pre‐Industrial conditions and ∼100 and ∼65 m³ s⁻¹ relative to mid‐20th century conditions. The LULCC effect was especially large in wet years, implying that current land cover is ill‐suited for buffering against extreme precipitation, likely in large part due to replacement of forest by cropland in the lower basin. Because increases in Missouri River flow over the past century were driven mostly by a recent (and likely transient) pluvial, our results suggest that flow in the basin could revert to a drier mean state when that pluvial ends, likely made worse by increased evaporative demand from anthropogenic warming.

Background Oral microbes detected in feces have been associated with colorectal cancer (CRC) in cross‐sectional studies. This study investigated the prospective associations between the oral microbiome and incident CRC in the Agricultural Health Study (AHS), National Institutes of Health–AARP (NIH‐AARP) Diet and Health Study, and Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial. Methods Individuals with oral samples collected before incident CRC diagnoses were identified in the AHS (N = 331), NIH‐AARP (N = 249), and PLCO (N = 446) and compared with referent subcohorts (N = 3431). The V4 region of the 16S ribosomal RNA gene was sequenced from oral wash DNA, and the data were processed with QIIME2. Hazard ratios (HRs) and 95% confidence intervals (CIs) for overall CRC and by anatomic subsite (i.e., proximal colon, distal colon, and rectum) were estimated with Cox proportional hazards models with adjustment for potential confounders by cohort and then meta‐analyzed. Results Overall, no associations were found between microbial characteristics and CRC risk. However, associations were observed with alpha and beta diversity indices and individual genera in analyses stratified by anatomic subsite. For instance, the presence of Olsenella was strongly positively associated with distal colon cancer risk (HR, 2.16; 95% CI, 1.59–2.95), whereas the presence of Prevotella 2 was positively associated with rectal cancer risk (HR, 1.68; 95% CI, 1.14–2.46). Conclusions This large study of the prospective association between the oral microbiome and CRC risk showed numerous site‐specific associations, including multiple associations with distal colon and rectal cancer risk.

Chloride salt‐bearing deposits are widely distributed across the southern highlands of Mars. Because chloride salts are highly water‐soluble, these deposits may be representative of the last significant period of stable liquid water at the Martian surface. Therefore, these deposits are key to understanding the fate and evolution of surface waters on Mars. However, little consensus exists about the formation conditions of these deposits, and their origins remain enigmatic. This is due in part because remote spectroscopic detection and quantification of many anhydrous chlorides is hampered by a lack of easily discernible diagnostic absorption features. To address this issue, we present a novel Hapke radiative transfer model‐based method to estimate hydration states and salt abundances of Martian chloride salt‐bearing deposits using visible/near‐infrared (VNIR) reflectance spectra. VNIR laboratory spectra are used to derive water abundances of analog chloride‐bearing materials, establishing an experimental basis for application of these methods to Mars. These methods are then applied to orbital Compact Reconnaissance Imaging Spectrometer for Mars data to create maps of the hydration state and modeled salt abundance of chloride‐bearing deposits. When overlain onto high resolution 3D digital terrain models, these methods produce the highest resolution site‐specific salt abundance maps currently available, enhancing our understanding of chloride deposit geologic context. As an example, deposits in the Terra Sirenum region are observed to have higher estimated salt abundances than previously recognized, exhibiting spatial variations in both abundance and surface morphology.

Baleen whales migrate from productive high-latitude feeding grounds to usually oligotrophic tropical and subtropical reproductive winter grounds, translocating limiting nutrients across ecosystem boundaries in their bodies. Here, we estimate the latitudinal movement of nutrients through carcasses, placentas, and urea for four species of baleen whales that exhibit clear annual migration, relying on spatial data from publicly available databases, present and past populations, and measurements of protein catabolism and other sources of nitrogen from baleen whales and other marine mammals. Migrating gray, humpback, and North Atlantic and southern right whales convey an estimated 3784 tons N yr⁻¹ and 46,512 tons of biomass yr⁻¹ to winter grounds, a flux also known as the “great whale conveyor belt”; these numbers might have been three times higher before commercial whaling. We discuss how species recovery might help restore nutrient movement by whales in global oceans and increase the resilience and adaptative capacity of recipient ecosystems.

Rapid Arctic warming this century will likely cause major water cycle and atmospheric circulation changes, including weakening mid‐latitude westerly winds and more persistent summer high pressures over Fennoscandia. These conditions can cause drought in northern Europe and extreme rainfall in the Mediterranean region. Uncertainties in the spatiotemporal patterns of these predictions can be partially addressed with records of past climate response to rapid change. The early Holocene collapse of the Northern Hemisphere ice sheets provides a natural experiment to evaluate the climate response to rapid changes in boundary conditions. We analyzed lipid biomarker distributions and hydrogen isotope (δ²H) values from Lake Imandra, Kola Peninsula, to infer Holocene summer temperature and summer precipitation δ²H values. Sensitivity tests of a lake model suggest summer precipitation δ²H values are the main mechanism influencing Lake Imandra δ²H values. Summer precipitation isotope values exhibited a nearly 20‰ ²H‐depletion between 8.6 and 8.0 ka, with ²H ‐enriched values before 8.6 ka and ²H ‐depleted values 8.0 ka to present. Maximum warmth occurred from 8.5 to 7.0 ka. Climate model experiments suggest that the early Holocene Laurentide Ice Sheet collapse caused a westward shift of the Fennoscandian summer high‐pressure center. This caused a decrease in the proportion of local, ²H‐enriched precipitation falling throughout Fennoscandia and an increase in far‐traveled, ²H‐depleted precipitation from the mid‐latitudes, circulation that persisted throughout the Holocene. These results illustrate the sensitivity of climate in Fennoscandia and show that circulation regime shifts can occur in response to changes in boundary conditions far upwind.

This project involved a multicultural team collaboratively co‐creating a climate change module by and for Indigenous people. Embracing the framework of cultural humility, we recognized the bidirectional learning inherent in the project and its role in mitigating power dynamics within the team. This endeavor underscored the significance of transparency, effective communication, respect, reciprocity, trust building, and sensitivity to cultural contexts. Our findings emphasized the need for locally grounded programs that echo local traditional wisdom. We discovered that fostering an environment conducive to active listening and patience is pivotal in establishing a secure space. Our research affirms the equal validity and importance of both Western and Traditional knowledge (TK) systems. Our findings revealed that using a premade university‐designed climate change curriculum wasn't effective for Indigenous participants in this study. Instead, we co‐created a bottom‐up menu‐style approach that could be tailored to the instructor's preference and program capabilities.

Allopatric speciation is a widely accepted hypothesis for species distributed across geographic barriers. Meanwhile, niche conservatism, the tendency of species to retain their ancestral ecological traits, helps reinforce genetic differentiation by stabilising species distributions over time and reducing the role of competition in shaping range boundaries. In contrast, hybridisation can occur at the edges of distribution after secondary contact following climatic or geological events, leading to a reduction in genetic divergence between divergent lineages. In this study, we investigated the role of geographic barriers, niche conservatism and gene flow in the speciation history of Diploderma species in Taiwan, where geographically distinct taxa share similar environmental preferences. By using ddRAD-seq data, seven distinct genetic clusters were identified with two putatively new cryptic species in D. brevipes and D. polygonatum. Most sister species pairs share similar climatic niches based on niche equivalency and similarity tests. We further detected significant historical gene flow between lineages of D. brevipes and D. polygonatum, where secondary contact might have occurred because of palaeoclimate changes and historical demographic expansion. Our results demonstrate that niche conservatism does not always act in concert to strengthen the result of allopatric speciation; instead, it may also lead to gene flow between divergent lineages following secondary contact. On the other hand, postdivergence gene flow may be a creating force generating phenotypic diversity in sexually selected traits in our study system. The underestimated species diversity of Diploderma in Taiwan requires further taxonomic work in the future.

Background Microorganisms are found in almost every environment, including soil, water, air and inside other organisms, such as animals and plants. While some microorganisms cause diseases, most of them help in biological processes such as decomposition, fermentation and nutrient cycling. Much research has been conducted on the study of microbial communities in various environments and how their interactions and relationships can provide insight into various diseases. Co-occurrence network inference algorithms help us understand the complex associations of micro-organisms, especially bacteria. Existing network inference algorithms employ techniques such as correlation, regularized linear regression, and conditional dependence, which have different hyper-parameters that determine the sparsity of the network. These complex microbial communities form intricate ecological networks that are fundamental to ecosystem functioning and host health. Understanding these networks is crucial for developing targeted interventions in both environmental and clinical settings. The emergence of high-throughput sequencing technologies has generated unprecedented amounts of microbiome data, necessitating robust computational methods for network inference and validation. Results Previous methods for evaluating the quality of the inferred network include using external data, and network consistency across sub-samples, both of which have several drawbacks that limit their applicability in real microbiome composition data sets. We propose a novel cross-validation method to evaluate co-occurrence network inference algorithms, and new methods for applying existing algorithms to predict on test data. Our method demonstrates superior performance in handling compositional data and addressing the challenges of high dimensionality and sparsity inherent in real microbiome datasets. The proposed framework also provides robust estimates of network stability. Conclusions Our empirical study shows that the proposed cross-validation method is useful for hyper-parameter selection (training) and comparing the quality of inferred networks between different algorithms (testing). This advancement represents a significant step forward in microbiome network analysis, providing researchers with a reliable tool for understanding complex microbial interactions. The method’s applicability extends beyond microbiome studies to other fields where network inference from high-dimensional compositional data is crucial, such as gene regulatory networks and ecological food webs. Our framework establishes a new standard for validation in network inference, potentially accelerating discoveries in microbial ecology and human health.

For decades, science and engineering education researchers in the United States have sought to understand ways to realize more equitable, student‐centered learning experiences within K‐12 classrooms. One important line of research aligned to this aim has centered on opportunities for developing and supporting students’ epistemic agency, focusing on shifting epistemic agency away from residing solely in the teacher toward instead being enacted across the collaborative classroom community. Yet, despite extant research around this area of inquiry, little is known about how students negotiate epistemic agency amongst themselves. As research begins to delve into these critical student dynamics, we argue that the field must explicitly account for the varied powered relations ingrained within school spaces and how those relations impact students’ learning experiences. We then offer an illustrative example of student data to share a possible direction for critical analysis that could offer insight into such powered relations and how they play out and impact students’ epistemic agency, specifically through the concept of epistemic exclusion. Finally, we conclude with a call to action for educators and researchers.

Better characterization of the relationship between recreation and human-caused wildfire ignitions is critical to inform prevention efforts as visitation to public land increases. Behaviors and attitudes towards fire prevention remain understudied but can provide key insights into decision-making and resource allocation for land managers. We conducted intercept surveys of 739 public land users across three USDA Forest Service (Forest Service) ranger districts with high incidences of human-caused fire ignition in the southwestern US. We found that visitors had diverse information seeking and planning behaviors related to human-caused wildfires and their prevention. Respondents across districts typically indicated a preference for one of three fire prevention approaches: engineering, education, or enforcement, although a subset of respondents did not gravitate towards any particular approach. This typol-ogy can be explained by user characteristics and recreation preferences. We suggest that a dynamic, place-based approach to human-caused wildfire prevention that aligns with local visitor characteristics is likely to have the greatest impact on risk reduction. We suggest that each land management unit should engage a combination of education, enforcement, and engineering strategies tailored to the kinds of visitors their jurisdiction receives. Consistent messaging across diverse platforms and venues that span geographically beyond the unit in question to intercept public land users prior to arrival is likely to reduce accidental or negligent ignition behaviors. Identifying avenues to disseminate changing fire conditions to public land users after arrival is central to raising awareness while protecting public safety.

Silviculture is the central discipline of forestry. It has always been influenced by changes in social and environmental conditions. Much has been accomplished in terms of advancing silviculture, including the culture, scope, and the goals and values it supports. However, we see that trends that initiated or strengthened during the last three decades are not well reflected in the current definition and this provides a barrier for further progress. Such trends include global change, an increased diversity of landowners and associated management goals, expectations of people with a wide range of values, and an acceptance of different ways of knowing. In this context, we see the benefit of providing a more holistic view. Thus, we propose to define silviculture as the “art and science of supporting and stewarding forest and woodland ecosystems and their ability to adapt in order to foster the diverse values of forest's contributions to people, including landowners, rights holders, communities and society". We discuss this proposed definition, specifically how it can lead to increased flexibility in silvicultural decisions, which can reflect a higher diversity of values and strengthen the adaptive capacity of forests. Furthermore, we discuss how addressing these trends requires a change in education.

Climate change is altering the timing of seasonal vegetation cycles (phenology), with cascading consequences on larger ecosystem processes. Therefore, understanding the drivers of vegetation phenology is critical to predicting ecological impacts of climate change. While numerous phenology models exist to predict the timing of the start of the growing season (SOS), there are fewer end-of-season (EOS) models, and most perform poorly in grasslands, since they were made for forests. Our objective was to develop an improved EOS grassland phenology model. We used repeat digital imagery from the PhenoCam Network to extract EOS dates for 44 diverse North American grassland sites (212 site-years) that we fit to 20 new and 3 existing EOS models. All new EOS models (RMSE = 22–33 days between observed and predicted dates) performed substantially better than existing ones (RMSE = 43–46 days). The top model predicted EOS after surpassing a threshold of either accumulated cold temperatures or dryness, but only after a certain number of days following SOS. Including SOS date improved all model fits, indicating a strong correlation between start- and end-of-season timing. Model performance was further improved by independently optimizing parameters for six distinct climate regions (RMSE = 4–19 days). While the best model varied slightly by region, most included similar drivers as the top all-sites model. Thus, across diverse grassland sites, EOS is influenced by both weather (temperature, moisture) and SOS timing. Incorporating these new EOS models into Earth System Models should improve predictions of grassland dynamics and associated ecosystem processes.