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MaryBeth Keifer

Publications and source records attributed to MaryBeth Keifer.

9 recordsLinked to original sources
USGS2026

Recovery trajectories of surface fuels and forest trees following prescribed fire in low elevation conifer forests of California and southern Oregon

Background Prescribed fire is commonly used to manage surface fuels and stand structure in dry coniferous forests in the western United States. While the effectiveness of prescribed fire to manage fuel loads and live forest structure has been well documented, less is known about the shape of recovery trajectories more than a decade following treatment. We used up to 30 years of longitudinal observations from > 180 monitoring plots treated with a single prescribed fire-only treatment across six national parks in California and Oregon to compare competing recovery trajectory models: generalized linear models (GLM) that presumed exponential trajectories over time, generalized additive models (GAM) that had maximum flexibility to fit responses, and generalized Michaelis–Menten models that describe an asymptotic recovery trajectory. Results The Michaelis–Menten model had the lowest median RMSE of the fuel recovery models, with predicted recovery times and maximal fuel loads tending to increase with increasing fuel particle size. However, predictive performance was similar between model forms. GAM best predicted forest structure, showing that stem density of live overstory trees (> 15 cm stem diameter) declined immediately following prescribed fire without appreciable postfire accumulation. Results for live stem biomass were similar, but with less pronounced reductions. Conclusions We found that reductions in surface fuel biomass from a single prescribed fire-only treatment can last for more than a decade for some fuel types. Our analysis also demonstrates that asymptotic models reasonably describe surface fuel recovery trajectories. However, we lack the evidence to definitively conclude that asymptotic models best describe postfire recovery, even with repeated observations of up to three decades postfire. We also found that stem density and biomass of live trees with stem diameter > 15 cm both declined in the first few years immediately following the fire, after which they remained relatively unchanged for the remainder of the observation period.

California, Oregon↗
USGS2026

Effects of repeat prescribed burning in dry coniferous forests in national parks of California

Background Prescribed fire is a common approach to reduce fuels and mitigate fire hazards. The accumulation of live and dead fuels following initial treatment means that repeated application of prescribed fire could be used to maintain this benefit. However, the effect of repeated prescribed fires is not well documented in many dry coniferous forests in the western United States. Here, we present observations of changes in live trees and surface fuels following two prescribed fires in dry coniferous forests in national parks of California. Results Changes in forest structure and accumulation of surface fuels were similar over time following initial-entry and second-entry fires. An exception was that repeated fires were associated with substantial reductions in stem density. There were smaller changes in live tree basal area and stem biomass. Conclusions Our results indicate that following initial-entry fires, subsequent burning maintained reductions in surface fuel loads without major inadvertent losses of live tree basal area and stem biomass, implying the survival of large trees.

California↗
USGS2020

The Fire and Tree Mortality Database, for empirical modeling of individual tree mortality after fire

Wildland fires have a multitude of ecological effects in forests, woodlands, and savannas across the globe. A major focus of past research has been on tree mortality from fire, as trees provide a vast range of biological services. We assembled a database of individual-tree records from prescribed fires and wildfires in the United States. The Fire and Tree Mortality (FTM) database includes records from 164,293 individual trees with records of fire injury (crown scorch, bole char, etc.), tree diameter, and either mortality or top-kill up to ten years post-fire. Data span 142 species and 62 genera, from 409 fires occurring from 1981-2016. Additional variables such as insect attack are included when available. The FTM database can be used to evaluate individual fire-caused mortality models for pre-fire planning and post-fire decision support, to develop improved models, and to explore general patterns of individual fire-induced tree death. The database can also be used to identify knowledge gaps that could be addressed in future research.

Scientific Data↗
USGS2017

Higher sensitivity and lower specificity in post-fire mortality model validation of 11 western US tree species

Managers require accurate models to predict post-fire tree mortality to plan prescribed fire treatments and examine their effectiveness. Here we assess the performance of a common post-fire tree mortality model with an independent dataset of 11 tree species from 13 National Park Service units in the western USA. Overall model discrimination was generally strong, but performance varied considerably among species and sites. The model tended to have higher sensitivity (proportion of correctly classified dead trees) and lower specificity (proportion of correctly classified live trees) for many species, indicating an overestimation of mortality. Variation in model accuracy (percentage of live and dead trees correctly classified) among species was not related to sample size or percentage observed mortality. However, we observed a positive relationship between specificity and a species-specific bark thickness multiplier, indicating that overestimation was more common in thin-barked species. Accuracy was also quite low for thinner bark classes (<1 cm) for many species, leading to poorer model performance. Our results indicate that a common post-fire mortality model generally performs well across a range of species and sites; however, some thin-barked species and size classes would benefit from further refinement to improve model specificity.

International Journal of Wildland Fire↗
USGS2016

Duration of fuels reduction following prescribed fire in coniferous forests of U.S. national parks in California and the Colorado Plateau

Prescribed fire is a widely used forest management tool, yet the long-term effectiveness of prescribed fire in reducing fuels and fire hazards in many vegetation types is not well documented. We assessed the magnitude and duration of reductions in surface fuels and modeled fire hazards in coniferous forests across nine U.S. national parks in California and the Colorado Plateau. We used observations from a prescribed fire effects monitoring program that feature standard forest and surface fuels inventories conducted pre-fire, immediately following an initial (first-entry) prescribed fire and at varying intervals up to >20 years post-fire. A subset of these plots was subjected to prescribed fire again (second-entry) with continued monitoring. Prescribed fire effects were highly variable among plots, but we found on average first-entry fires resulted in a significant post-fire reduction in surface fuels, with litter and duff fuels not returning to pre-fire levels over the length of our observations. Fine and coarse woody fuels often took a decade or longer to return to pre-fire levels. For second-entry fires we found continued fuels reductions, without strong evidence of fuel loads returning to levels observed immediately prior to second-entry fire. Following both first- and second-entry fire there were increases in estimated canopy base heights, along with reductions in estimated canopy bulk density and modeled flame lengths. We did not find evidence of return to pre-fire conditions during our observation intervals for these measures of fire hazard. Our results show that prescribed fire can be a valuable tool to reduce fire hazards and, depending on forest conditions and the measurement used, reductions in fire hazard can last for decades. Second-entry prescribed fire appeared to reinforce the reduction in fuels and fire hazard from first-entry fires.

Forest Ecology and Management↗
USGS2013

Climatic stress increases forest fire severity across the western United States

Pervasive warming can lead to chronic stress on forest trees, which may contribute to mortality resulting from fire-caused injuries. Longitudinal analyses of forest plots from across the western US show that high pre-fire climatic water deficit was related to increased post-fire tree mortality probabilities. This relationship between climate and fire was present after accounting for fire defences and injuries, and appeared to influence the effects of crown and stem injuries. Climate and fire interactions did not vary substantially across geographical regions, major genera and tree sizes. Our findings support recent physiological evidence showing that both drought and heating from fire can impair xylem conductivity. Warming trends have been linked to increasing probabilities of severe fire weather and fire spread; our results suggest that warming may also increase forest fire severity (the number of trees killed) independent of fire intensity (the amount of heat released during a fire).

Ecology Letters↗
USGS2004

Effects of an introduced pathogen and fire exclusion on the demography of sugar pine

An introduced pathogen, white pine blister rust ( Cronartium ribicola ), has caused declines in five-needled pines throughout North America. Simultaneously, fire exclusion has resulted in dense stands in many forest types, which may create additional stress for these generally shade-intolerant pines. Fire exclusion also allows fuels to accumulate, and it is unclear how affected populations will respond to the reintroduction of fire. Although white pine blister rust and fire exclusion are widely recognized threats, long-term demographic data that document the effects of these stressors are rare. We present population trends from 2168 individuals over 5–15 years for an affected species, sugar pine ( Pinus lambertiana ), at several burned and unburned sites in the Sierra Nevada of California. Size-based matrix models indicate that most unburned populations have negative growth rates (λ range: 0.82–1.04). The growth rate of most populations was, however, indistinguishable from replacement levels (λ = 1.0), implying that, if populations are indeed declining, the progression of any such decline is slow, and longer observations are needed to clearly determine population trends. We found significant differences among population growth rates, primarily due to variation in recruitment rates. Deaths associated with blister rust and stress (i.e., resource competition) were common, suggesting significant roles for both blister rust and fire exclusion in determining population trajectories. Data from 15 prescribed fires showed that the immediate effect of burning was the death of many small trees, with the frequency of mortality returning to pre-fire levels within five years. In spite of a poor prognosis for sugar pine, our results suggest that we have time to apply and refine management strategies to protect this species.

Ecological Applications↗
USGS2001

Restoring fire to wilderness: Sequoia and Kings Canyon National Parks

Sequoia and Kings Canyon National Parks, established in 1890, consist of 863,741 acres (349,551 ha) of Sierra Nevada foothills, mid-elevation conifer forest, and high-elevation alpine environment. The parks contain 36 giant sequoia (Sequoiadendron giganteum) groves, including the largest known tree, the General Sherman. Ninety-four percent of the parklands is in designated or proposed wilderness (fig. 1), with conditions resembling roadless areas in national forests.

Fire Management Today↗