Using Count Regression to Investigate Millennial-Scale Vegetation and Fire Response from Multiple Sites Across the Northern Rocky Mountains, USA

Fire · 2025-08-14

The Northern Rocky Mountains, USA contain a vast forested landscape, managed primarily by the federal government. This region contains some of the highest elevations forests and most iconic endangered and threatened species in the contiguous United States. The influence of human impacts and climate change are evident on the landscape today, with larger and more frequent fires impacting vegetation composition and recovery. This project uses paleoecological data from six lake sediment cores to investigate what drives fire across this region over the Holocene. Count regression was used to predict charcoal influx as a function of Pinus pollen accumulation rates (PAR) and percent. The results show that fire activity increases significantly with Pinus pollen, and that baseline fire activity varies significantly across sites, largely following an elevation gradient. The results of this analysis illustrate a novel way to use paleoecological data to provide valuable information to federal agencies as they prepare for future management of these ecologically valuable areas.

Using x-ray fluorescence to identify Mazama ash in the Lake Bonneville basin, Utah, USA

The Holocene · 2025-07-31 · 1 citations

Generalizable solutions are needed for identifying volcanic tephra in sedimentary records. We used x-ray fluorescence (XRF) analysis first to detect volcanic tephra material, followed by electron microprobe analysis to identify the tephra as Mazama ash (7682–7584 cal yr BP) in three sediment cores from the Lake Bonneville basin. We compare these records from varying environmental settings to evaluate tephra presence in the mid-Holocene. We suggest the preservation of tephras such as Mazama ash is tied to the environmental conditions in which they are deposited. Environments with standing water such as lakes or stable wetland springs are more likely to preserve identifiable ash material, while settings susceptible to alternating wet and dry conditions may retain only a trace elemental signature of a tephra due to physical erosion. We propose the development of tephra indices based on unique geochemistry is a useful tool for detection and identification of tephra material in sedimentary records. Here, we develop a Mazama Tephra Index (MTI), specific to Mazama ash in Lake Bonneville basin sediments: MTI = (Y + Zr + Nb)/Rb. We tested the applicability of the MTI and were successful in XRF detection of Mazama ash in all three records.

Holocene land cover change in North America: continental trends, regional drivers, and implications for vegetation–atmosphere feedbacks

Climate of the past · 2025-11-06 · 1 citations

Abstract. Land cover governs the biogeophysical and biogeochemical feedbacks between the land surface and atmosphere. Holocene vegetation–atmosphere interactions are of particular interest, both to understand the climate effects of intensifying human land use and as a possible explanation for the Holocene temperature conundrum, a widely studied mismatch between simulated and reconstructed temperatures. Progress has been limited by a lack of data-constrained, quantified, and consistently produced reconstructions of Holocene land cover change. As a contribution to the Past Global Changes (PAGES) LandCover6k Working Group, we present a new suite of land cover reconstructions with uncertainty for North America, based on a network of 1445 sedimentary pollen records and the REVEALS pollen–vegetation model (PVM) coupled with a Bayesian spatial model. These spatially comprehensive land cover maps are then used to determine the pattern and magnitude of North American land cover changes at continental to regional scales. Early Holocene afforestation in North America was driven by rising temperatures and deglaciation, and this afforestation likely amplified early Holocene warming via the albedo effect. A continental-scale mid-Holocene peak in summergreen trees and shrubs (8.5 to 4 ka) is hypothesized to represent a positive and understudied feedback loop among insolation, temperature, and phenology. A last-millennium decrease in summergreen trees and shrubs with corresponding increases in open land was likely driven by a spatially varying combination of intensifying land use and neoglacial cooling. Land cover trends vary within and across regions, due to individualistic taxon-level responses to environmental change. Major species-level events, such as the mid-Holocene decline in Tsuga canadensis (eastern hemlock), may have altered regional climates. The substantial land cover changes reconstructed here support the importance of biogeophysical and biogeochemical vegetation feedbacks to Holocene climate–carbon dynamics. However, recent model experiments that invoke vegetation feedbacks to explain the Holocene temperature conundrum may have overestimated land cover forcing by replacing Northern Hemisphere grasslands >30° N with forests, an ecosystem state that is not supported by these land cover reconstructions. These Holocene reconstructions for North America, along with similar LandCover6k products now available for other continents, serve the Earth system modeling community by providing better-constrained land cover scenarios and benchmarks for model evaluation, ultimately making it possible to better understand the regional- to global-scale processes driving Holocene land cover, carbon cycle, and climate dynamics.

Student responses to the climate crisis: managing distress and exploring support systems

International Journal of Sustainability in Higher Education · 2025-10-07 · 4 citations

Purpose This study explored how undergraduate students familiar with the climate crisis navigate climate-specific challenges in their personal lives, an area where knowledge is extremely inadequate. Design/methodology/approach The authors examined a broad range of adaptive (i.e. helpful) and maladaptive (i.e. unhelpful) strategies that students employ to manage their emotions concerning climate change, as well as resources that could help them adjust to the climate crisis. Quantitative and qualitative survey data were collected. Findings Students used various adaptive strategies to manage their emotions, including recreation, self-care, eco-friendly behaviors (such as changing habits, advocacy and volunteerism), personal and professional social support and actively seeking knowledge and positivity to empower themselves while participating in climate action. Furthermore, students suggested that having more professionally trained social support and resources for engaging in sustainable action would better help them adapt to the challenges posed by climate change. Gaining insights into effective methods for regulating climate impact can facilitate preventative and treatment strategies to cope with significant climate distress in young people. Practical implications The authors hope that the current lessons can inform pedagogy and help develop evidence-based mental health resources that equip current and future generations to effectively adapt to and mitigate the climate crisis. Originality/value The current findings shed light on eclectic approaches that university students adopt to manage their emotional responses to climate distress. They highlight that most students feel a dearth of resources available to them to effectively manage their personal climate distress and contribute to sustainability.

Holocene Land Cover Change in North America:  Trends, Drivers, and Feedbacks

2024-03-09

Land cover governs biogeophysical and biogeochemical feedbacks between the land surface and atmosphere. Holocene vegetation-atmosphere interactions are of particular interest, both to understand the climate effects of intensifying human land use and as a possible explanation for the Holocene Conundrum, a widely studied mismatch between simulated and reconstructed temperatures. Progress addressing the Conundrum has been limited by a lack of data-constrained, quantified, and consistent reconstructions of Holocene land cover change. Following protocols from PAGES LandCover6k, a network of 1445 sedimentary pollen records from the Neotoma Paleoecology Database, and the REVEALS pollen-vegetation model coupled with a Bayesian spatial model, we developed land cover reconstructions with uncertainty for North America for 25 time intervals spanning the Holocene. We use these spatially comprehensive land cover maps to determine the pattern and magnitude of land cover changes at continental to regional scales and discuss underlying ecological, climatic, and anthropogenic drivers. Finally, we infer Holocene radiative forcing from these land cover shifts.Major land cover changes in North America include: 1) Early Holocene afforestation is attributed to rising temperatures and deglaciation, which likely amplified early Holocene warming via the albedo effect; 2) A continental-scale mid-Holocene peak in summergreen trees and shrubs (8.5 to 4 ka) may have been caused by a positive and understudied feedback loop among insolation, temperature, and phenological seasonality.  3) A  last-millennium decrease in summergreen trees and shrubs with corresponding increases in open land, likely driven by intensifying land use and neoglacial cooling. Land cover trends vary within and across regions due to individualistic taxon-level responses to environmental change.  Major species-level events, such as the mid-Holocene decline of eastern hemlock, may have altered regional climates. The substantial land-cover changes reconstructed here underscore the importance of biogeophysical vegetation feedbacks to Holocene climate dynamics. Continental-scale radiative forcing inferred from land cover change indicates early and late pre-industrial Holocene warming interrupted by a mid-Holocene period of cooling and followed by cooling in the recent millenia. These forcings from natural vegetation change are of the same order of magnitude as global forcings resulting from changes in atmospheric greenhouse gas concentrations from 1750 to 2019.These Holocene reconstructions for North America serve the Earth system modeling community by providing better-constrained land cover scenarios and benchmarks for model evaluation, that improve the understanding of regional- to global-scale processes driving Holocene land cover dynamics.

Using Paleoecological Methods to Study Long-Term Disturbance Patterns in High-Elevation Whitebark Pine Ecosystems

Fire · 2024 · 2 citations

• Environmental science
• Ecology
• Geology

Pinus albicaulis (whitebark pine) is a keystone species, providing food and habitat to wildlife, in high-elevation ecological communities. In recent years, this important species has been negatively impacted by changes in fire regimes, increased Dendroctonus ponderosae (mountain pine beetle) outbreaks associated with human landscape and climate modification, and the continued impact of the non-native Cronartium ribicola (white pine blister rust). This research investigates changes in fire occurrence, the establishment of Pinus albicaulis, and fuel availability at a high-elevation site in the Sawtooth National Recreation Area, Idaho, USA. Charcoal and pollen analyses were used to reconstruct fire and vegetation patterns for Phyllis Lake, Idaho, USA, over the past ~8200 cal y BP. We found that significant fire episodes occurred when the pollen accumulation rates (PARs) indicated more arboreal fuel availability, and we identified that Pinus albicaulis became well established at the site ~7200 cal y BP. The high-elevation nature of Phyllis Lake (2800 m) makes this record unique, as there are not many paleorecords at this high elevation from the Northern Rocky Mountains, USA. Additional high-elevation sites in Pinus albicaulis habitats will provide critical insight into the long-term dynamics of this threatened species.

Holocene land cover change in North America: continental trends, regional drivers, and implications for vegetation-atmosphere feedbacks

2024-02-20 · 3 citations

Abstract. Land cover governs the biogeophysical and biogeochemical feedbacks between the land surface and atmosphere. Holocene vegetation-atmosphere interactions are of particular interest, both to understand the climate effects of intensifying human land use and as a possible explanation for the Holocene Conundrum, a widely studied mismatch between simulated and reconstructed temperatures. Progress has been limited by a lack of data-constrained, quantified, and consistently produced reconstructions of Holocene land cover change. As a contribution to the Past Global Changes (PAGES) LandCover6k Working Group, we present a new suite of land cover reconstructions with uncertainty for North America, based on a network of 1445 sedimentary pollen records and the REVEALS pollen-vegetation model coupled with a Bayesian spatial model. These spatially comprehensive land cover maps are then used to determine the pattern and magnitude of North American land cover changes at continental to regional scales. Early Holocene afforestation in North America was driven by rising temperatures and deglaciation, and this afforestation likely amplified early Holocene warming via the albedo effect. A continental-scale mid-Holocene peak in summergreen trees and shrubs (8.5 to 4 ka) is hypothesized to represent a positive and understudied feedback loop among insolation, temperature, and phenology seasonality. A last-millennium decrease in summergreen trees and shrubs with corresponding increases in open land likely was driven by a spatially varying combination of intensifying land use and neoglacial cooling. Land cover trends vary within and across regions, due to individualistic taxon-level responses to environmental change. Major species-level events, such as the mid-Holocene decline of eastern hemlock, may have altered regional climates. The substantial land-cover changes reconstructed here support the importance of biogeophysical vegetation feedbacks to Holocene climate dynamics. However, recent model experiments that invoke vegetation feedbacks to explain the Holocene Conundrum may have overestimated the land cover forcing by replacing Northern Hemisphere grasslands >30° N with forests; an ecosystem state that is not supported by these land cover reconstructions. These Holocene reconstructions for North America, along with similar LandCover6k products now available for other continents, serve the Earth system modeling community by providing better-constrained land cover scenarios and benchmarks for model evaluation, ultimately making it possible to better understand the regional- to global-scale processes driving Holocene land cover dynamics.

A late glacial paleoenvironmental and climate record from the Sierra de Juarez, Baja California

Quaternary International · 2024-07-04 · 3 citations

Ciénegas are desert wetlands that are strongly correlated with the stability of the hydrologic cycle in arid landscapes. However, these environments are particularly vulnerable to climate change, drought, water diversion, and fire suppression which all have contributed to the degradation of ciénegas along the U.S.-Mexican borderlands. Therefore, identifying the timing of precipitation patterns in this region is of particular interest because of its relationship to many ecological responses of the landscape such as groundwater recharge and fire. Here, we present the first-ever fire paleoenvironmental record from Ciénega Chimeneas, a ciénega complex in the Sierra de Juárez of Baja California. We explore how changes in the amount and seasonality of moisture affected ciénega complexes and fire activity from across the southwestern North American region over the past 45,000 years. Our record suggests that during the late glacial period, 41,000–21,000 cal yr BP, the increase of Larrea and Quercus indicate an increase in summer precipitation. Subsequently, when summer precipitation increased, pollen preservation and pollen accumulation rates (PAR) also increased. Increased vegetation allowed for increased fire activity during the late glacial period. Regionally, most of the comparison sites also indicated wet conditions during the full glacial period. However, around 21,000 cal yr BP, effective moisture decreased resulting in a dramatic change in the vegetation assemblage. Specifically, the summer wet taxa disappeared, while pollen preservation and PAR decreased, suggesting a dry period until ∼14,000 cal yr BP. Little fire activity is recorded after 21,000 cal yr BP, likely due to the absence of fuels. At ∼14,000 cal yr BP, Larrea and Quercus reappear suggesting increased summer precipitation. However, the appearance of Cyperaceae and increases in grasses suggest increased winter precipitation. We suggest that the combination of summer wet and winterwet taxa ∼14,000 cal yr BP represents an increase in ENSO conditions, while the summer moisture controls remained relatively constant.

Mosaic of somatic mutations in one of Earth’s largest organisms, Pando

bioRxiv (Cold Spring Harbor Laboratory) · 2024-10-22 · 10 citations

Abstract While evolutionary biology traditionally focuses on the spread of mutations within populations, the dynamics of mutational spread within individuals, particularly in long-lived clonally-spreading organisms, remain poorly understood. Here we examine the genetic structure of ‘Pando’, Earth’s largest known quaking aspen ( Populus tremuloides ) clone. We sequenced over 500 samples across Pando and neighboring clones, including multiple tissue types. At fine spatial scales, we detected significant genetic structure, particularly in leaf tissue, but this signal weakened across larger distances, suggesting either rapid root growth homogenizes the system over time or mechanisms exist that prevent widespread mutation transmission. Phylogenetic analyses date Pando between ∼12,000 and 37,000 years old, supported by continuous aspen pollen presence in nearby lake sediments. Tissues accumulated mutations at different rates, with leaves showing significantly higher mutation loads than roots or branches. This work provides the first quantitative age estimate for this remarkable organism and offers initial insights into the spatial dynamics of somatic mutation in a massive clonal plant. While our reduced-representation sequencing approach limits detection of rare variants, these findings establish a foundation for understanding how long-lived modular organisms accumulate and distribute genetic variation, questions that will benefit from future high-coverage whole-genome sequencing across tissues.

Supplementary material to "Holocene land cover change in North America: continental trends, regional drivers, and implications for vegetation-atmosphere feedbacks"

2024-02-20 · 2 citations