Malcolm North

• PhD
• Professor at University of California, Davis

Drawing upon over 100 years of scholarly work on microclimate, we first present an overview of the history, key references, and critical issues surrounding the collection and utilization of microclimate records in ecosystem studies. We place particular emphasis on addressing specific and pressing issues related to the applications of microclimate a...

Although recent large wildfires in California forests are well publicized in media and scientific literature, their cumulative effects on forest structure and implications for forest resilience remain poorly understood. In this study, we evaluated spatial patterns of burn severity for 18 exceptionally large fires and compared their cumulative impac...

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...

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...

Live shrubs in forest understories pose a challenge for mitigating wildfire risk with prescribed fire. Factors driving shrub consumption in prescribed fires are variable and difficult to explain. This study investigated spatial patterns and drivers of Sierra Nevada mixed-conifer forest shrub consumption in prescribed fires through analysis of high-...

Changing disturbance regimes and climate can overcome forest ecosystem resilience. Following high-severity fire, forest recovery may be compromised by lack of tree seed sources, warmer and drier postfire climate, or short-interval reburning. A potential outcome of the loss of resilience is the conversion of the prefire forest to a different forest...

The US Endangered Species Act has enabled species conservation but has differentially impacted fire management and rare bird conservation in the southern and western US. In the South, prescribed fire and restoration‐based forest thinning are commonly used to conserve the endangered red‐cockaded woodpecker (Picoides borealis; RCW), whereas in the We...

Quantifying historical fire regimes provides important information for managing contemporary forests. Historical fire frequency and severity can be estimated using several methods; each method has strengths and weaknesses and presents challenges for interpretation and verification. Recent efforts to quantify the timing of historical high-severity f...

Changing climate and a legacy of fire-exclusion have increased the probability of high-severity wildfire, leading to an increased risk of forest carbon loss in ponderosa pine forests in the southwestern USA. Efforts to reduce high-severity fire risk through forest thinning and prescribed burning require both the removal and emission of carbon from...

Changing climate and a legacy of fire-exclusion have increased the probability of high-severity wildfire, leading to an increased risk of forest carbon loss in ponderosa pine forests in the southwestern USA. Efforts to reduce high-severity fire risk through forest thinning and prescribed burning require both the removal and emission of carbon from...

Recent and projected increases in the frequency and severity of large wildfires in the western U.S. makes understanding the factors that strongly affect landscape fire patterns a management priority for optimizing treatment location. We compared the influence of variations in the local environment on burn severity patterns on the large 2013 Rim fir...

Forests sequester carbon from the atmosphere, helping mitigate climate change. In fire-prone forests, burn events result in direct and indirect emissions of carbon. High fire-induced tree mortality can cause a transition from a carbon sink to source, but thinning and prescribed burning can reduce fire severity and carbon loss when wildfire occurs....

Globally, wildfire size, severity, and frequency have been increasing, as have related fatalities and taxpayer-funded firefighting costs. In most accessible forests, wildfire response prioritizes suppression because fires are easier and cheaper to contain when small. In the United States, for example, 98% of wildfires are suppressed before reaching...

Coastal redwood (Sequoia sempervirens), the world's tallest tree species, rehydrates leaves via foliar water uptake during fog/rain events. Here we examine if bark also permits water uptake in redwood branches, exploring potential flow mechanisms and biological significance. Using isotopic labeling and microCT imaging, we observed that water entere...

Changing climate and a legacy of fire-exclusion have increased the probability of high-severity wildfire, leading to an increased risk of forest carbon loss in ponderosa pine forests in the southwestern USA. Efforts to reduce high-severity fire risk through forest thinning and prescribed burning require both the removal and emission of carbon from...

Fire in high-elevation forest ecosystems can have severe impacts on forest structure, function and biodiversity. Using a 105-year data set, we found increasing elevation extent of fires in the Sierra Nevada, and pose five hypotheses to explain this pattern. Beyond the recognized pattern of increasing fire frequency in the Sierra Nevada since the la...

More than a century of forest and fire management of Inland Pacific landscapes has transformed their successional and disturbance dynamics. Regional connectivity of many terrestrial and aquatic habitats is fragmented, flows of some ecological and physical processes have been altered in space and time, and the frequency, size and intensity of many d...

With air quality, liability, and safety concerns, prescribed burning and managed wildfire are often considered impractical treatments for extensive fuels reduction in western US forests. For California's Sierra Nevada forests, we evaluated the alternative and analyzed the amount and distribution of constraints on mechanical fuels treatments on USDA...

Forests are a significant part of the global carbon cycle and are increasingly viewed as tools for mitigating climate change. Natural disturbances, such as fire, can reduce carbon storage. However, many forests and dependent species evolved with frequent fire as an integral ecosystem process. We used a landscape forest simulation model to evaluate...

A principal challenge of federal forest management has been maintaining and improving habitat for sensitive species in forests adapted to frequent, low- to moderate-intensity fire regimes that have become increasingly vulnerable to uncharacteristically severe wildfires. To enhance forest resilience, a coordinated landscape fuel network was installe...

Background / Purpose: Treeline advance in response to climate change does not happen uniformly across the landscape nor does it happen identically for all species. Two species, bristlecone pine and limber pine, in the California White Mountains are both treeline species but it appears that the two species are responding differentially above treel...

Background/Question/Methods Large old-growth trees play critical roles in forests, sequestering carbon, providing habitat, and shaping future forest dynamics. Understanding growth-climate relationships of large old-growth trees is therefore important for assessing future forest productivity, while changes in growth-climate relationships may be pr...

Background/Question/Methods Previous work has characterized forest structure in stands of Sierra Nevada mixed-conifer forest following the reintroduction of an active fire regime. Areas with restored frequent fire are expected to have greater resilience to wildfire and other environmental stressors. However, with increasing incidence of wildfires...

Background/Question/Methods Stresses on Sierra Nevada forests are likely to rise as changing climatic conditions increase the frequency and intensity of wildfire and drought events. Forest reconstructions and field studies indicate one role of fire in increasing forest resilience is the creation of structural and habitat heterogeneity. Recent rese...

Background/Question/Methods Land management agencies use vulnerability assessment to predict how species distributions will be affected by abiotic changes and to inform its management decisions. With abiotic change, biotic interactions are also likely to be affected. Current vulnerability assessments lack an understanding of the mechanisms by whic...

Background/Question/Methods We studied whether the biophysical setting or experienced fire history exerted greater control over the physical structure of forests in Yosemite National Park, California, USA. In mountainous regions, topography creates a mosaic of biophysical settings that vary in precipitation, temperature, heat load, and slope posi...

Mapped estimates of forest aboveground biomass (AGB) at regular intervals are important in carbon cycle studies. In the southwestern United States, there have been extensive changes to forests over the last decade, due to wildfire, climate-driven insect outbreaks and disease, increasing forest-human interaction, resource exploitation, and increasin...

Widespread fire suppression and thinning have altered the structure and composition of many forests in the western United States, making them more susceptible to the synergy of large-scale drought and fire events. We examine how these changes affect carbon storage and stability compared to historic fire-adapted conditions. We modeled carbon dynamic...

Many high-elevation regions in the western USA are protected public lands that remain relatively undisturbed by human impact. Over the last century, however, nonnative trout and cattle have been introduced to subalpine wetland habitats used by sensitive amphibian species. Our study compares the relative importance of cattle and trout impact on amph...

Large trees (>76 cm breast-height diameter) are vital components of Sierra Nevada/Cascades mixed-conifer ecosystems because of their fire resistance, ability to sequester large amounts of carbon, and role as preferred habitat for sensitive species such as the California spotted owl. To investigate the likely performance of large trees in a rapidly...

In Mediterranean environments in western North America, historic fire regimes in frequent-fire conifer forests are highly variable both temporally and spatially. This complexity influenced forest structure and spatial patterns, but some of this diversity has been lost due to anthropogenic disruption of ecosystem processes, including fire. Informati...

In many forests of the western US, increased potential for fires of uncharacteristic intensity and severity is frequently attributed to structural changes brought about by fire exclusion, past land management practices, and climate. Extent of forest change and effect on understory vegetation over time are not well understood, but such information i...

With projected climate change, we expect to face much more forest fire in the coming decades. Policymakers are challenged not to categorize all fires as destructive to ecosystems simply because they have long flame lengths and kill most of the trees within the fire boundary. Ecological context matters: In some ecosystems, high-severity regimes are...

Fire suppression and past logging have dramatically altered forest conditions in many areas, but changes to within-stand tree spatial patterns over time are not as well understood. The few studies available suggest that variability in tree spatial patterns is an important structural feature of forests with intact frequent fire regimes that should b...

Background/Question/Methods Forests provide many ecosystem services, including significant carbon storage that can offset anthropogenic greenhouse gas emissions. Balancing carbon storage and ecosystem function in forests that evolved with frequent, low intensity fire regimes may require tradeoffs. Although fire exclusion increases carbon storage...

Background/Question/Methods: Forests sequester carbon from the atmosphere, helping mitigate climate change. Fire suppression in many dry, temperate forests has increased stem density and fuel loads, resulting in an increase in wildfire severity, which can kill much of the overstory converting the burned forest from a carbon sink to a source. Mech...

A full factorial design crossing overstory (O) and understory (U) thinning and prescribed burning (B) was started at Teakettle Experimental Forest, California, in 2001 with the aim of achieving shifts in species composition to favor fire-resistant pines over fir. The goal of the present study was to evaluate the use of metabolic changes as early in...

A forest carbon (C) offset is a quantifiable unit of C that is commonly developed at the local or regional project scale and is designed to counterbalance anthropogenic C emissions by sequestering C in trees. In cap-and-trade programs, forest offsets have market value if the sequestered C is additional (more than would have occurred in the absence...

Management efforts to promote forest resiliency as climate changes have often used historical forest structure and composition to provide general guidance for fuels reduction and forest restoration treatments. However, it has been difficult to identify what stand conditions might be fire and drought resilient because historical data and reconstruct...

The USDA Forest Service is implementing a new planning rule and starting to revise forest plans for many of the 155 National Forests. In forests that historically had frequent fire regimes, the scale of current fuels reduction treatments has often been too limited to affect fire severity and the Forest Service has predominantly focused on suppressi...

Background/Question/Methods Managers and the public are increasingly interested in restoring forests to a condition that is not only less likely to burn in an uncharacteristically severe wildfire, but is also ecologically diverse. Unfortunately, lack of adequate reference information hampers our ability to define restoration targets in many areas...

Background/Question/Methods A central challenge in managing Sierra Nevada forests has been trying to reduce fuel accumulations from decades of fire suppression without adversely impacting ecosystem attributes. In particular, fuels treatments are often slowed or stalled by concerns for maintaining or improving habitat for threatened species. Over...

Although research on spotted owls (Strix occidentalis) has increased dramatically in the last decade, factors influencing owl reproduction still are poorly known. This ongoing study uses 9 years of demographic data to analyze associations between owl reproduction and weather, cone crop abundance, and nest-site structure. Initial results indicate no...

Fire suppression and other past management practices in the western USA have led to dense conifer forests with high canopy cover and thick layers of surface fuels, changes likely to alter understory microclimate relative to historical conditions. Silvicultural treatments are used to restore forest resilience, but little is known about their microcl...

Significant differences in microclimate have been found within crowns of dispersed vs. clumped leave trees resulting from fuels reduction treatments in Sierra Nevada mixed-conifer forest. The question remained whether these differences in abiotic conditions might be biologically significant to arboreal epiphyte communities. The objective of our exp...

Fire once played an important role in shaping many Sierran coniferous forests, but reduced fire frequency and extent have altered forest conditions. Productive, mesic riparian forests can accumulate high stem densities and fuel loads, making them susceptible to high-severity fire. Fuels treatments applied to upland forests, however, are often exclu...

Many semi-arid coniferous forests in western North America have reached historically unprecedented densities over the past 150 years and are dominated by shade-tolerant trees. Silvicultural treatments generally open the canopy but may not restore shade-intolerant species. We determined crossover-point irradiance (CPI) (light at which the height gro...

Background/Question/Methods Following 90 years of fire suppression and fuels accumulation, Sierra Nevada forest management is often focused on reducing the risk of high-severity fire without compromising habitat for sensitive species. One method proposed for balancing these objectives is to manage forest landscapes for the heterogeneity of forest...

Fire plays an important role in shaping many Sierran coniferous forests, but longer fire return intervals and reductions in area burned have altered forest conditions. Productive, mesic riparian forests can accumulate high stem densities and fuel loads, making them susceptible to high-severity fire. Fuels treatments applied to upland forests, howev...

Forests contain the world's largest terrestrial carbon stocks, but in seasonally dry environments stock stability can be compromised if burned by wildfire, emitting carbon back to the atmosphere. Treatments to reduce wildfire severity can reduce emissions, but with an immediate cost of reducing carbon stocks. In this study we examine the tradeoffs...

The diets of a fungal specialist, northern flying squirrel (Glaucomys sabrinus (Shaw, 1801)), and a dietary generalist, lodgepole chipmunk (Neotamias speciosus (Merriam, 1890)), were examined in the old-growth, mixed-conifer forest at the Teakettle Experimental Forest in California’s southern Sierra Nevada. Spores of fungi were identified from feca...

The effects of management on soil carbon efflux in different ecosystems are still largely unknown yet crucial to both our understanding and management of global carbon flux. To compare the effects of common forest management practices on soil carbon cycling, we measured soil respiration rate (SRR) in a mixed-conifer and hardwood forest that had und...

The large carbon stores of many of the worlds' forests are prone to reversal from wildfire. Fuels treatments can reduce wildfire emissions but at an immediate carbon reduction cost. Comparing these tradeoffs in forest burned by wildfire, we found treatments reduced wildfire emissions by 58% but total carbon loss, including biomass removed, was high...

Past forest management practices, fire suppression, and climate change are increasing the need to actively manage California Sierra Nevada forests for multiple environmental amenities. Here we present a relatively low-cost, repeatable method for spatially parsing the landscape to help the U.S. Forest Service manage for different forest and fuel con...

Sequestered forest carbon can provide a climate change mitigation benefit, but in dry temperate forests, wildfire poses a reversal risk to carbon offset projects. Reducing wildfire risk requires a reduction in and redistribution of carbon stocks, the benefit of which is only realized when wildfire occurs. To estimate the time needed to recover carb...

Fire is an important ecological process in many western U.S. coniferous forests, yet high fuel loads, rural home construction and other factors have encouraged the suppression of most wildfires. Using mechanical thinning and prescribed burning, land managers often try to reduce fuels in strategic areas with the highest fuel loads. Riparian forests,...

In the western United States, mechanical thinning and prescribed fire are common forest management practices aimed at reducing potential wildfire severity and restoring historic forest structure, yet their effects on forest microclimate conditions are not well understood. We collected microclimate data between 1998 and 2003 in a mixed-conifer fores...

There have been few fire history studies of eastern Sierra Nevada forests in California, USA, where a steep elevation gradient, rain shadow conditions, and forest stand isolation may produce different fire regimes than those found on the range’s western slope. We investigated historic fire regimes and potential climate influences on four forest typ...

Climate change models for California's Sierra Nevada predict greater inter-annual variability in precipitation over the next 50 years. These increases in precipitation variability coupled with increases in nitrogen deposition from fossil fuel consumption are likely to result in increased productivity levels and significant increases in forest under...

Thinning to reduce wildfire hazard is a common management practice in frequent-fire forests of the American west, but it is uncertain whether projects will help regenerate fire-resistant, shade-intolerant pines. We studied naturally established saplings of six conifer species in mixed-conifer forest in northern California, USA to determine how thre...

Depending on management, forests can be an important sink or source of carbon that if released as CO2 could contribute to global warming. Many forests in the western United States are being treated to reduce fuels, yet the effects of these treatments on forest carbon are not well understood. We compared the immediate effects of fuels treatments on...

Background/Question/Methods Forest reconstructions and limited historical data are often used to infer desired conditions for fuels-treated forests. Most of these studies, however, provide incomplete information for how fire regimes and resulting forest structure varied across the landscape. Uniform fuels treatments do not provide high canopy cove...

Background/Question/Methods Mechanical thinning and prescribed fire are widely used in many fire-suppressed western forests to reduce fuels and restore ecosystem structure and function. These treatments should reduce competition for resources, increasing growth of the large leave trees and the treated stand's potential future carbon storage. Severa...

Background/Question/Methods Fire is an important ecological process in many western U.S. coniferous forests, yet high fuel loads and rural home construction lead to the suppression of most wildfires. Using mechanical thinning and prescribed burning, managers often try to reduce fuels in strategic areas with the highest fuel loads. Riparian forests...

Background/Question/Methods Depending on management, forests can be an important sink or source of carbon. The recent increase in frequency of large and severe fires due to past fire suppression and ongoing climate change represents risk in forest carbon offset investment. Under current carbon accounting mechanisms, all forest carbon offset projec...

Predicted changes in climate and increasing nitrogen deposition are likely to have significant impacts on species that have limited distributions or are already experiencing diminished population size. Arnica dealbata (A. Gray, Asteraceae), a listed sensitive species in Yosemite National Park, is endemic to California and has limited distribution w...

The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of multiple use management of the Nation's forest resources for sustained yields of wood, water, forage, wildlife, and recreation. Through forestry research, cooperation with the States and private forest owners, and management of the National Forests and Nationa...

Soil respiration (R S) is a major carbon pathway from terrestrial ecosystems to the atmosphere and is sensitive to environmental changes. Although commonly used mechanical thinning and prescribed burning can significantly alter the soil environment, the effect of these practices on R S and on the interactions between R S and belowground characteris...

Restoring Sierra Nevada mixed-conifer forests after a century of fire suppression has become an important management priority as fuel reduction thinning has been mandated by the Healthy Forests Restoration Act. However, in mechanically thinned stands there is little information on the effects of different patterns and densities of live-tree retenti...

Examinamos las preferencias de árboles para nidos de las ardillas (Glaucomys sabrinus) en un bosque de árboles viejos de coníferas mixtas en el Parque Nacional Yosemite en California. Seguimos 8 ardillas a 21 árboles para nidos de julio a septiembre del 2004. Las ardillas escogieron árboles para nidos que fueron más grandes en diámetros y más altos...

Prescribed burning and mechanical thinning are used to manage fuels within many western North American forest ecosystems, but few studies have examined the relative impacts of these treatments on forest wildlife. We sampled northern flying squirrels (Glaucomys sabrinus) and microhabitat variables in burned, thinned and control stands of mixed-conif...

With growing debate over the impacts of post-fire salvage logging in conifer forests of the western USA, managers need accurate assessments of tree survival when significant proportions of the crown have been scorched. The accuracy of fire severity measurements will be affected if trees that initially appear to be fire-killed prove to be viable aft...

Fire and thinning restoration treatments in fire-suppressed forests often damage or stress leave trees, altering pathogen and insect affects. We compared types of insect- and pathogen-mediated mortality on mixed-conifer trees 3years after treatment. The number of bark beetle attacked trees was greater in burn treatments compared with no-burn treatm...

Truffles are an important food resource for wildlife in North American forests, but decades of fire exclusion have altered the availability of this resource. In Yosemite National Park, resource management policies seek to restore essential forest processes such as fire while minimizing adverse ecological impacts that may result from burning decades...

Forests are viewed as a potential sink for carbon (C) that might otherwise contribute to climate change. It is unclear, however, how to manage forests with frequent fire regimes to maximize C storage while reducing C emissions from prescribed burns or wildfire. We modeled the effects of eight different fuel treatments on treebased C storage and rel...

In forests, high-severity burn patches—wherein most or all of the trees are killed by fire—often occur within a mosaic of low-and moderate-severity effects. Although there have been several studies of postfire salvage-logging effects on bird species, there have been few studies of effects on bird spe-cies associated with high-severity patches in fo...

Past riparian microclimate studies have measured changes horizontally from streams, but not vertically through the forest canopy. We recorded temperature and relative humidity for a year along a two-dimensional grid of 24 data-loggers arrayed up to 40 m height in four trees 2 -30 m slope distance from a perennial second order stream in the Sierra N...

Fire is a driver of ecosystem patterns and processes in forests globally, but natural fire regimes have often been altered by decades of active fire management. Following almost a century of fire suppression, many western U.S. forests have greater fuel levels, higher tree densities, and are now dominated by fire-sensitive, shade-tolerant species. T...

California's Sierra Nevada mountains are predicted to experience greater variation in annual precipitation according to climate change models, while nitrogen deposition from pollution continues to increase. These changes may significantly affect understory communities and fuels in forests where managers are attempting to restore historic conditions...