Climate change is raising the elevation of rain-snow transition lines and accelerating spring snowmelt, posing increasing risks to California's regional ecosystems and water infrastructure. Research has shown that snow accumulation and retention are shaped by complex interactions with forest structure. Open-canopy gaps tend to preserve snowpack better than closed-canopy forests. However, it is unclear how long these advantages persist as forests regenerate. This study examines how canopy gap age, defined as years since group selection harvest, affects snow depth across twenty-eight canopy gaps in the north-central Sierra Nevada. Multiple Linear regression models indicated that each additional year of canopy gap age corresponded to a 4.8% decline in March snow depth and a 0.3-day acceleration in snow disappearance, though these coefficients should be interpreted as indicative of direction and relative magnitude rather than precise predictions. Greater snow depth and later snow disappearance dates were both associated with younger canopy gaps, with these benefits declining approximately linearly over 30-40 years as regenerating cohorts grew and canopy closure progressed. Multivariate Autoregressive State-Space models showed that gap age was not a strong predictor of day-to-day snow depth; the time series was dominated by ablation periods during which snow depth loss was broadly similar across age classes. Combined with visual inspection of the season's snow depth patterns, this suggests that gap age primarily influences end-of-season snow depth through differences established during accumulation events rather than during ablation periods. Gap age may serve as a practical proxy for structural forest characteristics that are difficult to measure yet critically influence end-of-season snow depth and presence, though replication is needed to assess the robustness and predictive utility of this relationship across multiple water years. From a forest management perspective, gap-based silviculture such as group selection harvesting is a promising starting point for maintaining greater snow depth as a co-benefit alongside other management objectives. Advancing this understanding will require multi-year observations, comprehensive snowpack measurements, and closer examination of how young regenerating vegetation influences snowpack.

An industrial forester and a silviculture professor got into a friendly debate over how to manage a 40-year-old Sierra mixed-conifer stand. They both agreed it needed to be thinned and agreed on how much should be thinned, but they differed over how to thin it. The industrial forester argued for thinning from above. For the same amount of basal area removal, it would generate more revenue than any other thinning method, while still leaving the stand positioned to grow just as well post-treatment. The silviculturalist worried thinning from above would come at a cost. Even if subsequent stand-level volume production was unaffected (a questionable claim), the smaller trees reach maturity later, delaying the final harvest. Better to retain the largest trees, get to maturity quickly, and start the next rotation sooner. In 2016, a field trial was established to resolve the debate empirically. This paper is a companion to that project. Here, we explore the contested economic logic at the center of the argument. We aim to provide a conceptual foundation—developed analytically and illustrated graphically—for interpreting the empirical findings. We show that if post-treatment stand growth is the same for both methods, then thinning from above is financially preferable to thinning from below, despite delaying regeneration and contrary to silviculturalists’ customary skepticism of the method. We stop short of offering specific management recommendations, pending further results from the field trial, but identify the conditions that must hold for thinning from below to outperform thinning from above.

Background Following high-severity wildfires in conifer forests that rely on wind dispersal for regeneration, reforestation practices are used to hasten the development of large, fire-resistant trees that are better able to persist through the next fire. Planted forests, however, are particularly prone to high-severity wildfire effects for the initial decades following their establishment. This vulnerability suggests the need for surface fuel reduction treatments in the early stages of stand development. Such treatments would be aligned with the disturbance regime of frequent-fire forests and could also hasten the development of multi-aged structures dominated by fireresistant trees. Conventional treatments early in stand development include shrub competition reduction and precommercial thinning, but prescribed fire is typically avoided. To assess the potential for inclusion of prescribed fire in young stand management, we investigated how four different treatments – mastication, mastication plus herbicide, two prescribed burns, and mastication plus two burns – affected individual and stand-level growth versus fuel loads in young mixed-conifer plantations in the north-central Sierra Nevada, California, USA. Results Total surface fuel load more than doubled over five years in the mastication only and mastication plus herbicide treatments. Fuel accumulation was avoided in the two treatments that included prescribed fire. Stand growth was similar across the mastication only, mastication plus herbicide, and mastication plus burn treatments. Stand growth was lowest in the burn only treatment. The mastication plus herbicide treatment maximized individual tree growth, especially for white fir and incense-cedar. Individual tree growth was similar among the burn only, mastication only, and mastication plus burn treatments. Conclusions Mastication followed by repeated prescribed burning could be a viable management strategy to reduce wildfire hazard without sacrificing growth in young mixed-conifer stands that are entering a vulnerable stage of fire risk. Mastication in combination with herbicide may facilitate the growth of large, fire-resistant trees, but does not address surface fuel buildup. The use of fire alone can effectively reduce fuels, but stand growth may be somewhat low relative to mastication and herbicide. Incorporating prescribed fire is a promising approach for protecting planted stands from high-severity fire while transitioning them into multi-aged structures. Gapbased silvicultural systems that facilitate the development of multi-cohort stands can also use prescribed fire broadly in order to restore heterogeneity and low surface fuel loads.

The century-long era of fire suppression has resulted in dramatic decreases in giant sequoia regeneration and recruitment. A 2001 mechanical disturbance in a native grove created experimental canopy gaps ranging in size from 0.05 to 0.4 ha, where factors of giant sequoia recruitment were monitored. The patches of recruitment all burned in a 2021 wildfire, creating an opportunity to study fire-gap recruitment dynamics. The study questions were (1) what was the relationship between gap size and tree height up to the point of the fire, (2) which treeand gap-level variables explained mortality amongst the planted trees, and (3) did a pre-fire thin-and-prune treatment increase fire-related crown damage? There was an asymptotic relationship between average tree height and gap size. Increases in gap size beyond 0.2 ha led to only modest increases in average tree height. The overall mortality rate of study trees, averaged across gaps, was 26 %, ranging from 5.0 % to 52 %. A generalized linear mixed-effects model (GLMM) was fit to determine factors of mortality. Taller trees had lower probability of mortality, followed by trees closer to the centers of gaps. The pre-fire thin-and-prune treatment did not have a statistically significant effect on mortality or crown damage. A key finding was that canopy gaps facilitated giant sequoia recruitment by altering the resource environment while also altering patterns of fuel accumulation. Tree height was maximized in gaps greater than 0.2 ha, but gaps as small as 0.05 ha protected interior trees from fire.

Prescribed fires play a critical role in reducing the intensity and severity of future wildfires by systematically and widely consuming accumulated vegetation fuel. While the current probability of prescribed fire escape in the United States stands very low, their consequential impact, particularly the large wildfires they cause, raises substantial concerns. The most direct way of understanding this trade-off between wildfire risk reduction and prescribed fire escapes is to explore patterns in the historical prescribed fire records. This study investigates the spatiotemporal patterns of escaped prescribed fires in California from 1991 to 2020, offering insights for resource managers in developing effective forest management and fuel treatment strategies. The results reveal that the months close to the beginning and end of the wildfire season, namely May, June, September, and November, have the highest frequency of escaped fires. Under similar environmental conditions, areas with more records of prescribed fire implementation tend to experience fewer escapes. The findings revealed the vegetation types most susceptible to escaped prescribed fires. Areas with tree cover ranging from 20 to 60

Gap-based silviculture, which we define as the creation and maintenance of multi-aged stands through the periodic harvesting of discrete canopy gaps, provides a potential mechanism for converting previously high-graded stands into more heterogeneous, multi-aged structures. An advantage of small canopy gaps, relative to even-aged regeneration methods, is their potential to suppress shrub competition while allowing seedling growth without the use of herbicides or other means of managing shrub competition. While this idea has been proposed in principle, it has not been tested. The objective of this study was to evaluate the use of small canopy gaps, which were 0.08 ha in size with a mean ratio of gap diameter to border tree height of 1.3, as a method to regenerate four mixed-conifer tree species. Gaps were randomly treated either with or without herbicide in a Sierra Nevada mixed-conifer forest. Our hypothesis was that, if this opening size provided sufficient edge effect to control shrub competition, there would be no or little difference in seedling growth between herbicide-treated and control gaps. For all species planted, height and basal diameter growth trends over time were very similar between gaps treated with and without herbicide. The similarity in seedling growth occurred despite a substantial difference in shrub cover between untreated (43%) and treated gaps (3%). We interpret this as evidence that a gap structure such as the one tested can allow a co-occurrence of mediated shrub development and seedling recruitment and that the primary limitation on seedling growth comes from overstory trees, not shrubs. We demonstrate an example of the difference in seedling growth that can be expected between small gaps and clearcuts in order to discuss tradeoffs between these silvicultural systems. Following repeated measurements of seedlings for 7 years following planting, a wildfire burned across the study area, allowing for an additional assessment of wildfire-related seedling damage and mortality in gaps with differing levels of shrub abundance. Substantial mortality of study trees occurred following wildfire (62% mortality 1-year post-fire), but mortality was similar between treated and control gaps. This suggests that shrubs do not have a negative impact with respect to fire related mortality in small canopy gaps despite higher shrub cover. Gap-based silviculture could be a valuable tool for developing multi-aged, multi-species stands without the use of herbicide.

Wildfires are a significant threat to human health, in part through degraded air quality. Prescribed burning can reduce wildfire severity but can also lead to an increase in air pollution. The complexities of fires and atmospheric processes lead to uncertainties when predicting the air quality impacts of fire and make it difficult to fully assess the costs and benefits of an expansion of prescribed fire. By modeling differences in emissions, surface conditions, and meteorology between wildfire and prescribed burns, we present a novel comparison of the air quality impacts of these fire types under specific scenarios. One wildfire and two prescribed burn scenarios were considered, with one prescribed burn scenario optimized for potential smoke exposure. We found that PM2.5 emissions were reduced by 52%, from 0.27 to 0.14 Tg, when fires burned under prescribed burn conditions, considerably reducing PM2.5 concentrations. Excess short-term mortality from PM2.5 exposure was 40 deaths for fires under wildfire conditions and 39 and 15 deaths for fires under the default and optimized prescribed burn scenarios, respectively. Our findings suggest prescribed burns, particularly when planned during conditions that minimize smoke exposure, could be a net benefit for the impacts of wildfires on air quality and health.

Prescribed burning is an effective treatment to reduce the risk of very severe wildfires. Many forests, however, are ill-suited for prescribed fire, because of high fuel loads, high tree densities, or young stands that are vulnerable to low intensity fires. Utilizing prescribed fire in reforested stands established after high-severity fires can protect against further losses from subsequent wildfires (“reburn” fires). Only a handful of studies provide practical guidance on how and when to burn young forests. We apply the concept of “pyrosilviculture” to suggest ways in which pre-fire silvicultural treatments can make prescribed burns more effective across a variety of age classes and structures. We also update results from a study in which several age classes of stands (12-, 22-, 32-, and 100-year-old) were burned experimentally on the same day. This focuses on a key question for managers: how to determine the right stand age at which prescribed fires may become feasible. As expected, older stands were more resistant to damage and had higher survival rates. If tree survival during prescribed fires is a primary objective, then a conservative approach is to wait until stands are age 30 before instituting prescribed fire. This is likely an overestimate of the minimum age, given that the prescribed fires applied in this study occurred during especially dry conditions. Under different objectives, higher mortality may be considered beneficial if it creates low-density, high-complexity stands that are similar to historic conditions.

Background In ecosystems where fire has been excluded, pyrosilviculture can restore some processes historically maintained by fire while mitigating risk where fire is inevitable. Pyrosilviculture in crown fire-adapted forests is, however, limited by insight into the temporal window of fire return matching canopy seedbank development. Here, we characterized demographic responses to fire and non-native pine pitch canker infection in a chronosequence of serotinous bishop pine stands burned at high-severity to quantify (1) temporal patterns of seedbank development given seed viability and density, cone production, and tree density, and (2) pine pitch canker incidence across tree ages and sizes to assess how infection might impact stand and seedbank development. We use our findings to elucidate pyrosilvicuture as a means of restoring fire given practical challenges of reintroducing high-severity fire in crown-fire adapted forests embedded within wildland urban interfaces (WUI). Results Bishop pine produces an abundant, viable seedbank within eight years that persists across developmental stages and age classes. Seed abundance and viability are exceptionally high at even the earliest age (median > 600,000 seeds ha − 1 and 97% viability at 6 years) and remain high, with the oldest stands (36 years) maintaining median densities of > 500,000 seeds ha − 1 and viability of 95%. We additionally learned that pine pitch canker infection is most severe during the sapling stage (8–10 years post-fire), likely altering stand development trajectories as well as potentially limiting recruitment, and thus the aerial seedbank, into the canopy. Conclusions In bishop pine and equally-fecund serotinous species, pyrosilviculture appears a viable management tool across a broad fire return window given the early development and persistence of a robust, viable seedbank, allowing managers flexibility in restoring fire to promote forest persistence while simultaneously mitigating wildfire risk. Moreover, pyrosilviculture in pine pitch canker infected stands may also provide disease mitigation. Although the long-term effects of pine pitch canker infection remain unknown, bishop pines’ viable, persistent seedbank suggests that managers can ignite prescribed fire across a broad return interval — as short as eight years and as long as several decades — to promote bishop pine persistence, mitigate disease infection rates, and reduce wildfire risk in WUI-adjacent ecosystems.

Shaded fuel breaks are treatments that aim to mitigate wildfires by establishing linearly aligned locations where wildfire suppression efforts can be more effective at stopping wildfires. Despite the potential of fuel breaks to alter fire behavior, there have been limited quantitative assessments of their effectiveness following exposure to wildfires. In addition, wildfires often occur in complex terrains that are difficult to access with ground vehicles and sensors, posing challenges for data acquisition. However, the use of Remote-controlled Aerial Vehicles (RAVs), such as drones, is becoming increasingly popular as a viable means of conducting high-resolution ob-servations in areas of interest. This study presents the results from a unique opportunity to utilize three distinct observation scale platforms (in-situ, aerial, and spaceborne) to investigate the burn severity impacts across a prior shaded fuel break that serendipitously encountered the 2020 Creek Fire in the Sierra Nevada forests of California, USA. To provide a direct measure of fire severity, ground-based measurements determined the per-centage crown volume (PCV) of scorch and char as a function of distance from the fuel break edge. Along five transects of the fuel break, we also utilized visible bands from drone imagery and digital photogrammetry, to generate georeferenced orthophotos and quantify vegetation health using the Green Leaf Index (GLI). We also quantified burn severity by computing the Delta Normalized Burn Ratio (dNBR) and vegetation health using the Normalized Difference Vegetation Index (NDVI) from Sentinel 2 spaceborne observations. Our results indicate that within the fuel break, the PCV of char is 2 x less than it was outside of it (with PCV char declining at a rate of 2% per 3 m into the fuel break). Burn severity is 5 x less, and vegetation health is approximately 3 x greater within the fuel break compared to directly outside. Furthermore, postfire vegetation health was only 1 x less within the fuel break compared to the pre fire condition, whereas it was 5 x less in the surrounding region. The results confirm that the fuel break altered the fire behavior, reducing the fire intensity, thereby proving effective at reducing fire burn severity and preserving vegetation health within the fuel break.

The Internet-of-things ecosystem has been a driving force in the creation of smart communities where a variety of physical phenomena can be monitored continuously, e.g., air quality, traffic conditions on roads, energy consumption in buildings, etc. In this paper, we address how IoT can be quickly and effectively deployed for short-term and sporadic events (e.g., fire spread in a wildland area and flood propagation), where monitoring the evolving event is critical. In particular, we propose QuIC-IoT, a model-driven planning platform that aims to temporarily deploy a custom IoT infrastructure for monitoring short-term events, where phenomena-spread is driven by models that are physics-based. Our driving usecase event is a quasi-planned prescribed fire or RxFire - this is a wildfire resilience technique where intentional small fires are ignited apriori by forestry personnel to destroy fuel and help contain the spread of actual wildfires. Anomalies that may occur during these quasi-planned events must be rapidly captured by the IoT deployment, e.g., escaped RxFires can escalate to catastrophic wildfires under unpredictable conditions of wind, vegetation, etc. QuIC-IoT incorporates domain expert-developed models to guide IoT deployment; the event area is partitioned into subregions and a criticality metric that quantifies the likelihood of anomalies at each location is computed. QuIC-IoT allows us to mix fixed and quasi-mobile IoT devices to flexibly deploy IoT in challenging terrain and as the phenomena (RxBurn) evolves. We evaluate QuIC-IoT in two real-world forest settings (large and small) in Blodgett Forest, CA, USA, with concrete burn plans developed by wildfire experts. Our experimental results reveal that QuIC-IoT enables over 3X improvement in cost-effectiveness and performance (timely detection of anomalies) as compared to baseline IoT deployment algorithms.

Fire suppression and past selective logging of large trees have fundamentally changed frequent-fire-adapted forests in California. The culmination of these changes produced forests that are vulnerable to catastrophic change by wildfire, drought, and bark beetles, with climate change exacerbating this vulnerability. Management options available to address this problem include mechanical treatments (Mech), prescribed fire (Fire), or combinations of these treatments (Mech + Fire). We quantify changes in forest structure and composition, fuel accumulation, modeled fire behavior, intertree competition, and economics from a 20-year forest restoration study in the northern Sierra Nevada. All three active treatments (Fire, Mech, Mech + Fire) produced forest conditions that were much more resistant to wildfire than the untreated control. The treatments that included prescribed fire (Fire, Mech + Fire) produced the lowest surface and duff fuel loads and the lowest modeled wildfire hazards. Mech produced low fire hazards beginning 7 years after the initial treatment and Mech + Fire had lower tree growth than controls. The only treatment that produced intertree competition somewhat similar to historical California mixed-conifer forests was Mech + Fire, indicating that stands under this treatment would likely be more resilient to enhanced forest stressors. While Fire reduced modeled wildfire hazard and reintroduced a fundamental ecosystem process, it was done at a net cost to the landowner. Using Mech that included mastication and restoration thinning resulted in positive revenues and was also relatively strong as an investment in reducing modeled wildfire hazard. The Mech + Fire treatment represents a compromise between the desire to sustain financial feasibility and the desire to reintroduce fire. One key component to long-term forest conservation will be continued treatments to maintain or improve the conditions from forest restoration. Many Indigenous people speak of “active stewardship” as one of the key principles in land management and this aligns well with the need for increased restoration in western US forests. If we do not use the knowledge from 20+ years of forest research and the much longer tradition of Indigenous cultural practices and knowledge, frequent-fire forests will continue to be degraded and lost.

An essential component of sustainable forest management is accurate monitoring of forest activities. Although monitoring efforts have generally increased for many forests throughout the world, in practice, effective monitoring is complex. Determining the magnitude and location of progress towards sustainability targets can be challenging due to diverse forest operations across multiple jurisdictions, the lack of data standardization, and discrepancies between field inspections and remotely-sensed records. In this work, we used California as a multijurisdictional case study to explore these problems and develop an approach that broadly informs forest monitoring strategies. The State of California recently entered into a shared stewardship agreement with the US Forest Service (USFS) and set a goal to jointly treat one million acres of forest and rangeland annually by 2025. Currently, however, federal and state forest management datasets are disjoint. This work addresses three barriers stymying the use of federal and state archival records to assess management goals. These barriers are: 1) current databases from different jurisdictions have not been combined due to their distinct data collection processes and internal structures; 2) datasets have not been comprehensively analyzed, despite the need to understand the extent of previous treatments as well as the rate of current activity; and 3) the spatial accuracy of archival datasets has not been evaluated against remotely-sensed data. To reduce these barriers, we first aggregated existing archival forest management records between 1984 and 2019 from the USFS' Forest Activity Tracking System (FACTS) and the California Department of Forestry and Fire Protection (CAL FIRE) using a qualitative scalar of treatment intensity. Combined FACTS and CAL FIRE completed footprint acres - defined as unique areas of land where a treatment was completed at any time since 1984 - have decreased since a peak in 2008. At most, 300,000 footprint acres are completed each year, 30% of the million-acre goal. Prescribed fires - defined as direct burning operations - have risen over time, according to the FACTS hazardous fuels dataset but prescribed fire records in CAL FIRE's dataset have rapidly increased since 2016. We also refined the spatial and temporal detail of the aggregated management record using the Continuous Change Detection and Classification algorithm on satellite remote sensing data to produce a state-wide time series map of harvest disturbances. A comparison of the algorithm's refined data to the archival record potentially suggests over-reporting in both FACTS and CAL FIRE's archival datasets. Our integrated dataset provides a better assessment of current treatments and the path towards the 1-million-acre a year goal. The refined dataset leverages the strengths of complementary, albeit imperfect, monitoring strategies from archives and remotely-sensed detection.

Prescribed (Rx) burns are conducted on days when the meteorological thresholds of maximum air temperature, relative humidity, and wind speeds are all met (burn window) in order to ensure safe Rx burn practices. Limited burn windows have been consistently identified as one of the most important constraints for conducting Rx burns in California. We investigate whether burn windows across California can be extended from the typical fall season to include other opportune seasons for facilitating specific management objectives. We quantify the seasonal Rx burn efficiencies by assessing the frequency and burned areas using an aggregate of Rx datasets, and we compute the seasonal spatiotemporal trends in the number of days the set of meteorological parameters are met over thirty-five years (1984 to 2019), using the gridMET 4 km dataset. Our results indicate that while fall burns are most frequently executed (40% of the time), the spring (and to a lesser extent winter) seasons yield efficient Rx burns similar to fall because greater acres are being consumed with less burns. In addition, winter and spring seasons experience burn window opportunities (70-90% of the time) over larger areas than the other seasons, and this is predominantly over forested regions in Northern California. Our results also indicate that burn windows in the winter and spring are decreasing at a rate of one day per year over a larger spatial area than that of summer and fall. This decrease is primarily driven by changes in the number of days the relative humidity thresholds are met. Policymakers recognize the critical importance that Rx burns have on a multitude of ecosystem restoration factors, fire behavior dynamics, and firefighter safety. Therefore, there is a need to capitalize on these additional burn windows before these opportunities become less feasible in the future.

In dry, productive forests where historically infrequent high-severity fires are now common, new silvicultural systems will be needed to better align management activity with the ecosystem's dependent disturbance regime of frequent low and moderate-severity fires. Merging timber harvests with prescribed fire programs can be advantageous because each disturbance provides benefits that the other cannot provide alone. We conducted a study aimed at providing information to managers interested in merging gap-based silviculture with frequent prescribed fire. We studied the influence of burn season (spring versus fall) on canopy mortality and damage by conducting prescribed burns in 13-14 year old stands that had been regenerated with gap-based silviculture. We also pruned sugar pine (Pinus lambertiana) and incense-cedar (Calocedrus decurrens) prior to burns to evaluate the influence of pruning on fire related mortality and damage. Fall (21%) and spring (19%) burns resulted in similar amounts of mortality two years following burns, but the fall burns consumed considerably more fuel compared to spring burns. Percent volume crown scorch was greater in spring burns and greater when crown bases were low to the ground. Fall burns were generally favorable assuming a management context where fuel consumption and survival is desirable. However, either burn season may be acceptable using fire as a thinning mechanism is desired to encourage the development of low-density, mature stands. As a pre-fire treatment, pruning did not clearly reduce fire-related mortality or crown damage. Considering that pruning itself is a form of crown damage, it could be considered counterproductive as a pre-fire treatment because of increased heat entering pruned crowns as a result of increased surface fuel and the loss of heat-buffering lower branches. Merging gap-based silviculture with prescribed fires in perpetuity may be initially complex operationally in the Sierra Nevada, but it offers managers a disturbance regime-guided method for sustaining heterogeneity at fine and coarse scales while maintaining low surface fuels. The timing of introducing fires into young stands as well as traditional timber management tools such as rotation ages and harvest intervals can be altered depending on exact objectives.

Background In the wake of increasingly frequent and severe wildfires in California, artificial regeneration and density management facilitate prompt reforestation and the rapid growth of large, fire-resistant trees. Young plantations are particularly prone to high-severity wildfire effects, suggesting the implementation of fuel reduction treatments in the early stages of stand development. The extent to which density management ( i.e. , thinning) and fuels management ( i.e. , prescribed fire) can work together is uncertain given their potentially conflicting effects on tree and stand level growth. We investigated how four different treatments – mastication, mastication plus herbicide, two prescribed burns, and mastication plus two burns – affected individual and stand-level growth versus fuel loads in mixed-conifer plantations during young stand development in the north-central Sierra Nevada, California, USA. Results The mastication plus herbicide treatment maximized individual tree growth, especially for white fir and incense-cedar, but fuel loads doubled after five years without the use of fire. The mastication only treatment resulted in a 151% increase in fuel loads over the same period, and individual tree growth was comparable to the burn only and mastication plus burn treatments. The burn only treatment greatly decreased fuel loads but also resulted in low relative stand growth. The mastication plus burn treatment prevented fuel accumulation and generally did not slow down individual tree growth. In addition, stand growth occurred at a rate similar to that of the mastication plus herbicide treatment. Conclusions Mastication followed by repeated prescribed burning could be a viable management strategy to reduce wildfire hazard without sacrificing growth in young mixed-conifer stands that are entering a vulnerable stage of fire risk. Mastication in combination with herbicide may grow trees to a large, fire-resistant size more quickly, but does not address fuel buildup. The use of fire alone can effectively reduce fuels while not substantially impacting individual tree growth, but stand growth may decline relative to mastication and herbicide.

As fire regimes shift in western North America, patches of stand-replacing fire are becoming larger. Forest succession in these patches is not well understood. There is concern that competition with rapidly reestablishing shrubs, combined with dispersal limitation, may delay or impede conifer recovery and/or shift tree composition toward shade-tolerant species. However, tree–shrub interactions and shrub neighborhood dynamics have not been closely examined. To investigate the patterns and processes determining forest recovery after severe wildfire, we developed a data-driven simulation model that we use to predict conifer emergence above the shrub canopy. Our model results showed that ponderosa pine (Pinus ponderosa) emerged at a faster rate than white fir (Abies concolor) under whitethorn ceanothus (Ceanothus cordulatus) and deerbrush (Ceanothus integerrimus), and at a similar rate under greenleaf manzanita (Arctostaphylos patula). Across all shrub species, ponderosa pine had a relative advantage over fir in the period between conifer establishment and peak shrub competition, requiring a mean of 16 years for 50% of individuals to emerge compared to 22 years for fir. Fir emergence rates then surpassed those of pine, leading to similar overall emergence by simulation end: 83% ± 7% for pine and 82% ± 7% for fir. These results show that, on balance, shrub neighborhood dynamics do not produce an ecological filter favoring firs for the initial cohort of established seedlings, but emergence patterns are sensitive to shrub species. Further applications of this data-driven simulation framework could improve understanding of other important components of post-fire succession.

Background Young, planted forests are particularly vulnerable to wildfire. High severity effects in planted forests translate to the loss of previous reforestation investments and the loss of future ecosystem service gains. We conducted prescribed burns in three ~35-year-old mixed conifer plantations that had previously been masticated and thinned during February in order to demonstrate the effectiveness of winter burning, which is not common in the Sierra Nevada, California. Results On average, 59% of fine fuels were consumed and the fires reduced shrub cover by 94%. The average percent of crown volume that was damaged was 25%, with no mortality observed in overstory trees 1 year following the fires. A plot level analysis of the factors of fire effects did not find strong predictors of fuel consumption. Shrub cover was reduced dramatically, regardless of the specific structure that existed in plots. We found a positive relationship between crown damage and the two variables of Pinus ponderosa relative basal area and shrub cover. But these were not particularly strong predictors. An analysis of the weather conditions that have occurred at this site over the past 20 years indicated that there have consistently been opportunities to conduct winter burns. On average, 12 days per winter were feasible for burning using our criteria. Windows of time are short, typically 1 or 2 days, and may occur at any time during the winter season. Conclusions This study demonstrates that winter burning can be an important piece of broader strategies to reduce wildfire severity in the Sierra Nevada. Preparing forest structures so that they can be more feasible to burn and also preparing burn programs so that they can be nimble enough to burn opportunistically during short windows are key strategies. Both small landowners and large agencies may be able to explore winter burning opportunities to reduce wildfire severity. Antecedentes Las plantaciones jóvenes son particularmente vulnerables a los incendios. Los efectos de una alta severidad del fuego en plantaciones jóvenes se convierten en pérdidas de las inversiones previas en la reforestación y también en pérdidas de ganancias futuras en los servicios ecosistémicos. Condujimos quemas prescriptas en tres plantaciones de coníferas mixtas de aproximadamente 33 años de edad que había sido previamente raleadas y trituradas. La quema se realizó durante febrero para demostrar la efectividad de las quemas de invierno, lo cual no es común en las Sierras Nevadas de California, EEUU. Resultados En promedio, el 59% de los combustibles finos fueron consumidos y las quemas redujeron la cobertura de arbustos en un 94%. El porcentaje promedio del volumen de copa que fue dañado alcanzó el 25%, sin mortalidad observada en los doseles de los árboles un año después de la quema. Un análisis a nivel parcela de los factores que incidieron en los efectos del fuego no mostraron fuertes predicciones en el consumo de combustibles. La cobertura de arbustos fue reducida dramáticamente, independientemente de la estructura existente en cada parcela. Encontramos una relación positiva entre el daño a las copas y dos variables de Pinus ponderosa como área basal relativa y cobertura de arbustos. Desde luego, ambos no fueron predictores importantes. Un análisis de las condiciones ambientales que ocurrieron en este sitio en los últimos 20 años indicó que había habido consistentemente períodos en los cuales se hubiesen podido realizar quemas prescriptas. En promedio, en 12 días por cada invierno hubiese sido posible realizar estas quemas de acuerdo a nuestros criterios. Dentro de ellos, las ventanas de prescripción en el tiempo fueron cortas, típicamente de uno a dos días, pudiendo presentarse en cualquier momento durante el invierno. Conclusiones Este estudio demuestra que las quemas de invierno pueden ser una parte importante de estrategias más amplias para reducir la severidad de los incendios en las Sierras Nevadas . El preparar las estructuras forestales de manera que puedan ser más factibles de quemar y a la vez preparar programas de quema que puedan ser lo suficientemente ágiles como para quemar convenientemente durante los períodos cortos en los que las ventanas de oportunidad lo permiten, se tornan en estrategias claves. Tanto los pequeños propietarios como las grandes agencias de administración de recursos pueden explorar las quemas de invierno para reducir la severidad de los incendios.

Giant sequoia is a famously massive and long-lived tree endemic to the Sierra Nevada of California, whose persistence is threatened by a changing climate and an altered disturbance regime. One approach for protecting threatened species is to incorporate them into working landscapes. In a forestry context, the objectives of a working landscape include the production of timber and the storage of carbon. Given its potential for rapid growth, an understanding of the growth-density relationships for giant sequoia is a necessity for planning future management for these common management objectives. To investigate the effect of initial planting density on both individual tree and stand level characteristics, we used repeated measures data from a 28-year-old giant sequoia spacing trial. After 28 years, survival among all spacing treatments was high (>98%). Individual bole volume increased with greater growing space allocated per tree. Although initial relative growth rates based on bole volume differed among spacing treatments, relative growth rates were similar after 21 years. At the stand level, total stand volume was similar across all spacing treatments after 28 years. However, wider spacing treatments exhibited higher amounts of merchantable volume. After 28 years, stands of giant sequoia sequestered approximately 92.2 Mg ha(-1) across all spacing treatments. Our results show that giant sequoias are able to produce merchantable timber at a young age and sequester large amounts of carbon in a relatively short amount of time, supporting that giant sequoia is a promising candidate species for planting for timber production as well as carbon sequestration.