Larissa L. Yocom

• Utah State University

The El Niño Southern Oscillation (ENSO) is a climate-forcing mechanism that has been shown to affect precipitation and the occurrence of wildfires in many parts of the world. In the southern United States and northern Mexico, warm events (El Niño) are associated with moist winter conditions and fewer fires, while cool events (La Niñia) tend to favo...

Dendrochronologists studying fire history must be strategic in their search for fire-scarred tree samples. Because it is desirable to extend the period of analysis in a site by looking for old scars, recent scars, and trees with large numbers of scars, researchers have developed rules of thumb regarding which trees are most likely to meet these goa...

Two ends of the fire regime spectrum are a frequent low-intensity fire regime and an infrequent high-intensity fire regime, but intermediate fire regimes combine high- and low-severity fire over space and time. We used fire-scar and tree-age data to reconstruct fire regime attributes of mixed-conifer and aspen forests in the North Rim area of Grand...

Rapid increases in wildfire area burned across North American forests pose novel challenges for managers and society. Increasing area burned raises questions about whether, and to what degree, contemporary fire regimes (1984–2022) are still departed from historical fire regimes (pre-1880). We use the North American tree-ring fire-scar network (NAFS...

Background High-severity burned areas can have lasting impacts on vegetation regeneration, carbon dynamics, hydrology, and erosion. While landscape models can predict erosion from burned areas using the differenced normalized burn ratio (dNBR), post-fire erosion modeling has predominantly focused on areas that have recently burned. Here, we develop...

In western North America, quaking aspen stands (Populus tremuloides Michx.) have predominantly been described as low flammability, “fireproof” forests, but the specific relationship between aspen stand composition, fuel characteristics, and potential fire behavior is not fully understood. We investigated surface and canopy fuel characteristics in 8...

Background High-severity burned areas can have lasting impacts on vegetation regeneration, carbon dynamics, hydrology, and erosion. Landscape models can predict erosion from burned areas using the differenced normalized burn ratio (dNBR), but so far post-fire erosion modelling has been limited to areas that already burned. Here, we developed and va...

Background Wildfire is a major contemporary socio-ecological issue facing the people and natural resources of Southern California, and the prospect that a warming climate could lead to a higher probability of fire in the future is cause for concern. However, connecting climate change to projected burn probability is complex. While most models gener...

Increasing fire severity and warmer, drier postfire conditions are making forests in the western United States (West) vulnerable to ecological transformation. Yet, the relative importance of and interactions between these drivers of forest change remain unresolved, particularly over upcoming decades. Here, we assess how the interactive impacts of c...

After more than a century of low fire activity in the western United States, wildfires are now becoming more common. Reburns, which are areas burned in two or more fires, are also increasing. How fires interact over time is of interest ecologically as well as for management. Wildfires may act as fuel treatments, reducing subsequent fire severity, o...

Accurate assessment of burn severity is a critical need for an improved understanding of fire behavior and ecology and effective post-fire management. Although NASA Landsat satellites have a long history of use for remotely sensed mapping of burn severity, the recently launched (2015 and 2017) European Space Agency Sentinel-2 satellite constellation...

Post‐fire debris flows represent one of the most erosive consequences associated with increasing wildfire severity and investigations into their downstream impacts have been limited. Recent advances have linked existing hydrogeomorphic models to predict potential impacts of post‐fire erosion at watershed scales on downstream water resources. Here w...

Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree‐ring fire scars provide valuable perspectives on fire regimes, including centuries‐long records of fire year, season, frequency, severity, and size. Here, we introduce the...

Spatial patterns of precipitation in the southwestern United States result in a complex gradient from winter-to-summer moisture dominance that influences tree growth. In response, tree growth exhibits seasonal-to-annual variability that is evident in the growth of whole tree rings, and in sub-annual sections such as earlywood and latewood. We evalu...

O período entre 2018 e 2022 mostrou-nos que o problema dos incêndios à escala global não está a diminuir, antes pelo contrário. Parece que as consequências das alterações climáticas já estão a afectar a ocorrência de incêndios florestais em várias partes do Mundo, de uma forma que só esperaríamos que acontecesse vários anos mais tarde. Em muitos pa...

Background The epidemic Dendroctonus rufipennis (spruce beetle) outbreak in the subalpine forests of the Colorado Plateau in the 1990s killed most larger Picea engelmannii (Engelmann spruce) trees. One quarter century later, the larger snags are beginning to fall, transitioning to deadwood (down woody debris) where they may influence fire behavior,...

The increasing incidence of wildfires across the southwestern United States (US) is altering the contemporary forest management template within historically frequent-fire conifer forests. An increasing fraction of southwestern conifer forests have recently burned, and many of these burned landscapes contain complex mosaics of surviving forest and s...

We review science‐based adaptation strategies for western North American (wNA) forests that include restoring active fire regimes and fostering resilient structure and composition of forested landscapes. As part of the review, we address common questions associated with climate adaptation and realignment treatments that run counter to a broad conse...

Implementation of wildfire‐ and climate‐adaptation strategies in seasonally dry forests of western North America is impeded by numerous constraints and uncertainties. After more than a century of resource and land use change, some question the need for proactive management, particularly given novel social, ecological, and climatic conditions. To ad...

Sexual regeneration is increasingly recognized as an important regeneration pathway for aspen in the western United States, a region previously thought to be too dry for seedling establishment except for during unusually wet periods. Because of this historical assumption, information on aspen seedling establishment and factors influencing its occur...

Quaking aspen (Populus tremuloides) is an important component of western U.S. forests, however knowledge concerning processes of aspen seedling establishment, survival, and growth is limited and frequently anecdotal. Following a widespread post-fire establishment event in southern Utah, we explored spatial establishment patterns of >1000 aspen seed...

Trees are long-lived organisms that integrate climate conditions across years or decades to produce secondary growth. This integration process is sometimes referred to as ‘climatic memory.’ While widely perceived, the physiological processes underlying this temporal integration, such as the storage and remobilization of non-structural carbohydrates...

Wildfires pose significant risks to populations living in the Wildland-Urban Interface (WUI). We examine the influence of WUI residents’ risk perceptions as well as other cognitive constructs (guided by Protection Motivation Theory) likely to influence their decisions to take wildfire mitigation actions before and shortly after a near-miss wildfire...

Mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins) causes extensive tree mortality in whitebark pine (Pinus albicaulis Engelm) forests. Previous studies conducted in lodgepole pine (Pinus contorta Douglas), Douglas-fir (Pseudotsuga menziesii (mirb.) Franco), and Engelmann spruce (Picea engelmanni Parry ex. Engelm) have shown that litter, d...

In trees, large uncertainties remain in how non-structural carbohydrates (NSCs) respond to variation in water availability in natural, intact ecosystems. Variation in NSC pools reflects temporal fluctuations in supply and demand, as well as physiological coordination across tree organs in ways that differ across species and NSC fractions (e.g., sol...

Skillful multi-year climate forecasts provide crucial information for decision-makers and resource managers to mitigate water scarcity, yet such forecasts remain challenging due to unpredictable weather noise and the lack of dynamical model capability. Here we demonstrate that the annual water supply of the Colorado River is predictable up to sever...

Background/Question/Methods In the western United States, aspen (Populus tremuloides Michx.) is a species of particular importance, contributing disproportionally to biodiversity in the region. Aspen is frequently cited as an important fuel break because it is thought to be less likely to support crown fire than dense conifer stands. In some areas...

Quaking aspen is a common component of postdisturbance landscapes, in part because of its ability to regenerate via asexual suckers. Previously viewed as exceedingly rare in the western United States, sexual seedling establishment is increasingly seen as another important natural regeneration pathway for aspen, because sexual regeneration increases...

The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics, including reducing tree density and decreasing levels of woody biomass on the forest floor. However, reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass, with po...

Widespread, rapid aspen (Populus tremuloides Michx.) mortality since the beginning of the 21st century, sometimes called sudden aspen decline (SAD), has been documented in many locations across North America, but it has been particularly pronounced in the southwestern United States. We investigated the relationship among aspen growth, mortality, an...

Over the last several decades in forest and woodland ecosystems of the southwestern United States, wildfire size and severity have increased, thereby increasing the vulnerability of these systems to type conversions, invasive species, and other disturbances. A combination of land use history and climate change is widely thought to be contributing t...

Fire shapes landscapes long after the flames are extinguished by leaving legacies of heterogeneous fuel mosaics, species composition patterns, and age classes. Fire perimeters have received little research attention, but their locations have implications for both landscape patterns and processes, including vegetation structure and subsequent distur...

Decision makers need better methods for identifying critical ecosystem vulnerabilities to changing climate and fire regimes. Climate-wildfire-vegetation interactions are complex and hinder classification and projection necessary for development of management strategies. One such vulnerability assessment (VA) is FireCLIME VA, which allows users to c...

The western United States remains well below historical wildfire activity, yet misconceptions abound in the public and news media that the area burning by wildfire each year in the American West is unprecedented. We submit that short-term records of wildfire and a disproportionate focus on recent fire trends within high-profile science stoke these...

Background/Question/Methods Tree rings are often analyzed to reconstruct past climate or disturbances, but there is much to be learned about tree growth responses from tree rings. Traditional approaches to inferring climate from tree rings involve a series of steps to remove age effects, long-term trends that could mask the climate signal, and auto...

Wildfire is a key disturbance agent in forests worldwide, but recent large and costly fires have raised urgent questions about how different current fire regimes are from those of the past. Dendroecological reconstructions of historical fire frequency, severity, spatial variability, and extent, corroborated by other lines of evidence, are essential...

The occurrence of wildfire is influenced by a suite of factors ranging from “top-down” influences (e.g., climate) to “bottom-up” localized influences (e.g., ignitions, fuels, and land use). We carried out the first broad-scale assessment of wildland fire patterns in northern Mexico to assess the relative influence of top-down and bottom-up drivers...

The prevailing paradigm in the western U.S. is that the increase in stand-replacing wildfires in historically frequent-fire dry forests is due to unnatural fuel loads that have resulted from management activities including fire suppression, logging, and grazing, combined with more severe drought conditions and increasing temperatures. To counteract...

Global climate change will lead to shifts in climate patterns and fire regimes in the Southwest over the coming decades. The intent of this working paper is to summarize the current state of scientific knowledge about climate change predictions in the Southwest as well as the pathways by which fire might be affected. While the paper is focused on t...

This working paper discusses several methods for reconstructing historical fire regimes: • Historical documents and photos • Dendrochronology: fire-scar data • Dendrochronology: tree age, death and growth data • Forest structure data • Plant traits • Charcoal Each of these methods will be discussed in terms of advantages, disadvantages, inherent un...

We investigated the influence of broad- v. fine-scale factors on fire in an unusual landscape suitable for distinguishing the drivers of fire synchrony. Our study was conducted in the Sierra Madre Oriental mountain range, in north-eastern Mexico. We worked in nine sites on three parallel mountains that receive nearly identical broad-scale climatic...

Resumen. El bosque de Pinus hartwegii constituye el límite superior arbóreo en las montañas de México. En este estudio se desarrolló una red de cronologías de esta especie, localizadas en volcanes del Eje Neovolcánico Transversal, en el centro del país, y picos elevados de la Sierra Madre Oriental, en el noreste. El Análisis de Componentes Principa...

Fuel treatments are common and are generally regarded as beneficial for reducing fire behavior, as well as for ecological reasons such as increasing understory diversity and reducing competition among trees for nutrients and water. What remains unclear is how long such fuel treatments are effective in reducing undesirable fire behavior. This workin...

El propósito de este estudio fue generar una cronología de anillos de crecimiento lo más extensaposible y usarla como un método indirecto para el desarrollo de una reconstrucción de precipitaciónestacional en el Parque Nacional de Basaseachi (BNP), Chihuahua, México. Para el desarrollo de lacronología, se colectaron núcleos de crecimiento de ejempl...

En el noroeste de Chihuahua, sitio Mesa de las Guacamayas, catalogada como “Área Natural Protegida” ( ANP ) para anidamiento de la cotorra serrana, se desarrolló una serie dendrocronológica con abeto Douglas ( Pseudotsuga menziesii ) con una extensión de 409 años (1600-2008). La cronología de anillo total mostró asociaciones signi - ficativas (r>0....

The purpose of this study was to reconstruct the precipitation at Basaseachi National Park (BNP) in Chihuahua, Mexico.Tree-ring samples from pine species including Pinus durangensis, P. lumholtzii and P.engelmannii were collected in and near BNP and they were cross-dated with existing chronologies. Ring widths of each sample were measured and model...

Surface fire has increasingly been regarded as a critical threat to tropical forests, but much of the research documenting degradation of tropical forests by fire comes from the low‐elevation humid tropics. Fire in high‐elevation tropical forests has received less research attention, but these forests are of high conservation value because they sup...

Old-growth forests are biologically and ecologically valuable systems that are disappearing worldwide at a rapid rate. México still holds large areas covered by temperate forests in the mountains of the Sierra Madre Occidental, but few of these retain old-growth characteristics. We studied four sites with remnant old-growth forests in Mesa de las G...

The "pyroclimatic hypothesis" proposed by F. Biondi and colleagues provides a basis for testable expectations about climatic and other controls of fire regimes. This hypothesis asserts an a priori relationship between the occurrence of widespread fire and values of a relevant climatic index. Such a hypothesis provides the basis for predicting spati...

The breeding biology of Australian passerines is characterised by long breeding seasons and the potential to produce multiple broods within a single season. However, many species undergo a yearly migration from their breeding sites to climatically milder wintering grounds. This migratory behaviour may impose constraints on the breeding biology of t...