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The National Fire and Fire Surrogate Study: effects of fuel reduction methods on forest vegetation structure and fuels
Ecological Applications
Abstract
Changes in vegetation and fuels were evaluated from measurements taken before and after fuel reduction treatments (prescribed fire, mechanical treatments, and the combination of the two) at 12 Fire and Fire Surrogate (FFS) sites located in forests with a surface fire regime across the conterminous United States. To test the relative effectiveness of fuel reduction treatments and their effect on ecological parameters we used an information‐theoretic approach on a suite of 12 variables representing the overstory (basal area and live tree, sapling, and snag density), the understory (seedling density, shrub cover, and native and alien herbaceous species richness), and the most relevant fuel parameters for wildfire damage (height to live crown, total fuel bed mass, forest floor mass, and woody fuel mass).
In the short term (one year after treatment), mechanical treatments were more effective at reducing overstory tree density and basal area and at increasing quadratic mean tree diameter. Prescribed fire treatments were more effective at creating snags, killing seedlings, elevating height to live crown, and reducing surface woody fuels. Overall, the response to fuel reduction treatments of the ecological variables presented in this paper was generally maximized by the combined mechanical plus burning treatment. If the management goal is to quickly produce stands with fewer and larger diameter trees, less surface fuel mass, and greater herbaceous species richness, the combined treatment gave the most desirable results. However, because mechanical plus burning treatments also favored alien species invasion at some sites, monitoring and control need to be part of the prescription when using this treatment.
... Studies investigating how the understory plant community responds to mechanical restoration treatments in dry conifer forests have yielded mixed results with respect to the direction, magnitude, and timing of effect (Schwilk et al. 2009;Abella and Springer 2015;Willms et al. 2017). Changes in overall understory abundance and diversity were variable one to three years after treatment, with both increases and decreases commonly reported (Collins et al., 2007;Dodson et al., 2008;Wayman and North, 2007). ...
... Mechanical restoration treatments in dry conifer forests have been implemented in many different places with varying conditions throughout the western US (Schwilk et al., 2009;Stephens et al., 2012), yet little is known about how biologically meaningful environmental gradients affect understory responses to treatments Jang et al., 2021;Kane et al., 2010). It is possible that variations in topography and climate may modify understory responses following treatment; cooler and wetter sites may be able to support more understory vegetation post-treatment than their warmer, drier counterparts (North et al., 2005). ...
... In this study, gains in native species were accompanied by gains in non-native richness and cover in treated plots by 4-6 years after treatment (Figs. 2 and 3; Table 3). While restoration treatments are critically needed to increase dry conifer forest resilience to wildfire and other disturbances, preventing non-native species proliferation in the process is also a high priority (Collins et al. 2007;Schwilk et al. 2009;Jang et al. 2021). Monitoring in treated areas should continue for non-native species like cheatgrass (a prolific seeder) and Canada thistle (a strong vegetative spreader) which showed a clear affinity for treated areas. ...
Restoration efforts are underway in dry conifer forests across the western United States to increase their resilience to wildfire and other disturbances. Because such treatments typically decrease overstory density and homogeneity, they can also drive changes in the understory plant community. Past studies of post-treatment changes in understories have found variable results over short time frames and across regions, highlighting the need to study longer-term, region-specific responses. We investigated whether mechanical restoration treatments benefited understory plants in dry conifer forests of the Colorado Front Range, and what biotic and abiotic variables modified understory plant responses in treated areas. We analyzed data collected 1–2 years pre-treatment, 1–2 years post-treatment, and 4–6 years post-treatment in 168 plots, which were distributed across 8 sites and 16 pairs of treated and nearby untreated areas. Treatments were implemented by removing trees with heavy machinery or hand tools (i.e., thinning). By the time treatments were 4–6 years old, native understory plant cover was 1.7 times higher in treated compared to untreated plots, and native richness was 1.1 times higher. Heightened cover and richness values in treated plots were not driven by a single native plant functional group, but by a large portion of the native community; long-lived, graminoid, vegetatively spreading, and non-vegetatively spreading plants all had higher cover in treated plots, while short-lived, long-lived, forb, graminoid, and non-vegetatively spreading plants had higher richness in treated plots. Non-native plants showed 3.1 times higher cover and 4.4 times higher richness in treated compared to untreated plots at 4–6 years post-treatment, but were present at very low levels (e.g., ≤ 0.5% mean cover in either treatment). Greater native plant cover and richness at 4–6 years post-treatment were associated with lower overstory basal areas that resembled 19th-century forest structural conditions for the landscape. Contrary to expectations, a long-term measure of moisture availability (i.e., 30-year average climatic water deficit) was not a strong predictor of native cover or richness in treated plots 4–6 years post-treatment; rather, they were better predicted by moisture availability during the spring months prior to sampling. Overall, the consistent and enduring stimulation of cover and richness of native understory plants after mechanical treatments, with only limited invasion from non-native species, illustrates the important benefits of ongoing restoration activities in dry conifer forests of the Colorado Front Range.
... Perhaps the broadest and most comprehensive study of fuel treatment effectiveness was the National Fire and Fire Surrogates Study (NFFS) supported by Forest Service R&D and the Joint Fire Science Program and led by scientists from Forest Service R&D, USGS, and numerous university partners (McIver et al. 2012, Schwilk et al. 2009). The 12-site NFFS was a multivariate experiment that evaluated landscape and ecological consequences of alternative fuel management treatments in seasonally dry forests of the United States. ...
... Mechanical treatments did not serve as surrogates for fire for most ecological factors, suggesting that wildland fire must be maintained whenever possible. Restoring and maintaining resilient landscapes will require repeated treatments over time, with eastern forests requiring more frequent applications (McIver et al. 2012, Schwilk et al. 2009). During the past several years, the Joint Fire Science Program has had an active line of work investigating fuel treatment effectiveness (see http://www.firescience.gov ...
... regimes are usually expressed as wildfire frequency, extent, pattern, and severity(Agee 1993, Bowman et al. 2009, Brown and Smith 2000, Keeley et al. 2009, Morgan et al. 2001. Note that in the context of fire ecology, fire severity refers to the effects of wildland fires on landscape and ecosystem components, including the human dimensions (Hardy 2005). ...
This report focuses on wildland fire management and response outcomes—in the context of fire and fuels research and development (R&D) at the Forest Service, an agency of the U.S. Department of Agriculture (USDA)—that have transformed the business of wildland fire in the United States. This research has resulted in knowledge, data, and applications that have contributed greatly to the following outcomes.
Outcome 1. Enhanced Physical Fire Science
Wildland fire managers and responders are able to predict the occurrence, extent, and severity of fires with more precision and accuracy resulting in better decisionmaking, resource allocation, and firefighter and public safety. National systems that characterize fire danger and risk are maintained and innovated.
Outcome 2. Better Access to Smoke and Emissions Tools
Practitioners and regulators have access to information and tools for estimating smoke and emissions from wildland fire to support decisions about suppression, managed wildfires, and prescribed fire implementation, primarily to address firefighter and public health and safety.
Outcome 3. Advanced Wildland Fuels Management
Wildland fuels are characterized using consistent and comprehensive science and technology to meet diverse objectives and ensure effective investment strategies to restore resilient landscapes, mitigate wildfire risk, and deliver benefits to the public.
Outcome 4. Improved Social and Economic Context for Wildland Fire Management and Response
The public is aware of the costs and benefits of wildland fire management and response, and socioeconomic research and development are foundations for large landscape collaboration, organizational performance and effectiveness, and firefighter and public safety. Fire management organizations have access to information and tools to improve performance through learning and innovative leadership.
Outcome 5. Strengthened Wildland Fire Ecology Practices Supporting Landscape Restoration
Diverse and comprehensive information and tools that characterize the ecologic costs and benefits of fire are avail¬able to support the restoration of resilient landscapes; deliver clean, abundant water; and strengthen communities. Accessible science and technology exist for adaptive and collaborative fire management in the face of changing baseline conditions.
... Although improved resilience and protection of biodiversity are goals of proposed adaptation management, active management may, in some cases, have little effect on future stand resistance (Morris et al., 2022), is often unnecessary for natural forest resilience (e.g., Cansler et al., 2022;Hart et al., 2015) and biodiversity (Thom & Seidl, 2016;Viljur et al., 2022), and is generally counterproductive to carbon storage, structural complexity, tree diversity, and resistance to invasive species. (Donato et al., 2013;Miller et al., 2018;Patton et al., 2022;Schwilk et al., 2009;Young et al., 2017; Table 1). Moreover, conservation evidence for the effectiveness of management interventions is often lacking or has mixed results (Sutherland et al., 2021), resources for interventions are limited, and management incurs substantial financial and other costs to society (Houtman et al., 2013). ...
... In some cases, thinning has been shown to reduce subsequent tree death from insects and drought compared to untreated areas, thereby promoting stand resistance and maintaining an existing species composition, while procuring sound timber (Hood et al., 2016;Knapp et al., 2021). However, in other cases prescribed burn treatments increased subsequent tree mortality (Knapp et al., 2021;Stark et al., 2013;Youngblood et al., 2009), and thinning and burn treatments generally promote the spread of invasive plants relative to controls (Schwilk et al., 2009;Willms et al., 2017). Additionally, loss of tree basal area and carbon storage from thinning and prescribed burning is often equal to or considerably greater than tree mortality and carbon loss from the disturbances themselves Hood et al., 2016;Knapp et al., 2021;Powers et al., 2010;Yocom-Kent et al., 2015). ...
... Management strategy and outcome (+ positive; À negative; ? unknown)Schwilk et al., 2009, Donato et al., 2013Miller et al., 2016;Young et al., 2017;Stiers et al., 2018, Shell et al., 2021Patton et al., 2022 ...
Abstract Forests are critical to the planetary operational system and evolved without human management for millions of years in North America. Actively managing forests to help them adapt to a changing climate and disturbance regime has become a major focus in the United States. Aside from a subset of forests wherein wood production, human safety, and experimental research are primary goals, we argue that expensive management interventions are often unnecessary, have uncertain benefits, or are detrimental to many forest attributes such as resilience, carbon accumulation, structural complexity, and genetic and biological diversity. Natural forests (i.e., those protected and largely free from human management) tend to develop greater complexity, carbon storage, and tree diversity over time than forests that are actively managed; and natural forests often become less susceptible to future insect attacks and fire following these disturbances. Natural forest stewardship is therefore a critical and cost effective strategy in forest climate adaptation.
... High-severity wildfires kill large numbers of trees, creating dead woody fuels that are deposited on the forest floor over time as the dead trees decay, thereby increasing potential fire severity (Peterson et al. 2015, Ritchie et al. 2013). In contrast, low-severity fires-and most prescribed fires-consume surface fuels without generating large amounts of new woody fuels, thereby limiting future fire severity (Safford et al. 2012, Schwilk et al. 2009). ...
... Forest restoration treatments-particularly those with fuel reduction and fire resilience objectives-often seek to modify overstory stand structure and surface woody fuels with the goal of reducing future wildfire severity Skinner 2005, Allen et al. 2002). These treatments typically employ mechanical thinning of overstory trees and prescribed burning, alone or in combination (Allen et al. 2002, Schwilk et al. 2009). As noted earlier, prescribed fires are generally low-severity fires that consume surface fuels and thereby limit future fire severity for 10 to 15 years (Prichard et al. 2010, Safford et al. 2012. ...
... As noted earlier, prescribed fires are generally low-severity fires that consume surface fuels and thereby limit future fire severity for 10 to 15 years (Prichard et al. 2010, Safford et al. 2012. Mechanical thinning treatments can reduce potential fire severity by reducing the likelihood of crown fire occurrence but may also increase surface woody fuels if not combined with prescribed fire (Schwilk et al. 2009). ...
... Timber harvesting may sometimes be used as a fuel management technique, e.g., thinning (Agee and Skinner, 2005;Proctor and McCarthy, 2015;Keenan et al., 2021), but more generally it is a process to extract timber. Timber harvesting influences fine fuel both directly via addition of harvesting residue and indirectly by changing stand structure and fine fuel accumulation (Schwilk et al., 2009;Stephens et al., 2009;Hood et al., 2020). Post-harvest burning is often applied following harvesting to reduce the fine and coarse fuels created by the harvesting operation and promote regeneration of canopy species (Florence, 2004). ...
... Post-harvest burning is often applied following harvesting to reduce the fine and coarse fuels created by the harvesting operation and promote regeneration of canopy species (Florence, 2004). The type of harvesting operation and equipment used will influence forest regeneration, the growing conditions (e.g., light availability) and future fine fuel inputs (McCaw et al., 2002;Schwilk et al., 2009;Campbell et al., 2016). For example, selective harvesting where some mature trees are retained may have a different effect on fine fuel than clear-felling, as litter inputs from some mature trees are maintained and fewer gaps are created. ...
... The effect of different combinations of thinning (a form of timber harvesting) and prescribed burning on fine fuel has been studied extensively for North American forests. Generally, thinning followed by burning gives the best results for wildfire risk reduction, as it produces stands with fewer, larger trees and less surface litter (Schwilk et al., 2009;Waldrop et al., 2010). However, this reduction in wildfire risk may be offset by increased shrub cover following thinning and burning in some forest systems (Odland et al., 2021). ...
Forests are managed for a range of ecological and economic values. Prescribed burning and timber harvesting are two widely used and often co-occurring forest management activities. Both may alter wildfire risk by changing fuel characteristics. Prescribed burning alters the amount and arrangement of fuel, which changes the probability of ignition and rate of fire spread. Timber harvesting may influence future fuel composition, amount and structure directly via the addition of harvesting residue and indirectly by changing stand structure and fine fuel accumulation. Whilst there is reasonable understanding of how fuel changes immediately after a single prescribed burn or harvest in temperate eucalypt forests, the long-term effects of frequent prescribed burning combined with timber harvesting are poorly understood. We used a long-term (∼25 year) prescribed burning experiment conducted in ∼1000 ha of temperate eucalypt forest in southeastern New South Wales, Australia to determine the effects of a single selective timber harvest and 0–6 subsequent prescribed burns on the accumulation and composition of fine fuel (<25 mm thickness). It was found that fine fuel loads differed between harvested and unharvested stands, with 30 % less leaves and fine twigs (<6 mm) in the litter bed but 24 % more green understorey fuel up to 10 years post-burn in harvested stands. Frequent prescribed burning did not change total fine fuel load in harvested stands but did change fine fuel composition, with 4 times more leaves in the litter bed and 6 times less green understorey fuel in plots burnt at high frequencies (>4 fires in 25 years) versus low frequencies (0 fires in 25 years). Similar trends were observed in unharvested stands following frequent burning, however, there was 45% more leaves in the litter bed of frequently burnt, unharvested stands compared to frequently burnt, harvested stands. Our results suggest that irrespective of harvesting, frequent burning (>4 fires over 25 years) in temperate eucalypt forest may be a suitable strategy for lowering wildfire risk as it can reduce the amount of green understorey fuel, which may reduce flame heights and the likelihood of canopy fire. However, the decrease in green understorey fuel may be offset by the increase in leaves in the litter bed, which support fire ignition and spread. Our results highlight how the presence of timber harvesting changes the accumulation and composition of fine fuel post-fire, yet timber harvesting is currently not well integrated into many landscape fuel models, which often focus solely on time since last fire. Overlooking key attributes of disturbance history (timber harvesting, number of past fires), may jeopardise the accuracy of fuel models, and therefore the reliability of fire behaviour predictions.
... Past management (Agee and Lolley, 2006;Agee and Skinner, 2005;Hessburg et al., 2015;Schwilk et al., 2009) and prior fires (Parks et al., 2015a;Prichard et al., 2017;Stephens et al., 2009;Stevens-Rumann et al., 2016) influence the spread, intensity, and severity of subsequent fires. Silviculture and fire, including both prescribed and wildfire, are thus the main tools that managers can use to restore ecological resilience and resistance, and direct ecosystems toward conditions that will be more resilient under future climates Millar et al., 2007;Schuurman et al., 2020). ...
... We found that management treatments that include prescribed fire were most effective at decreasing the severity of subsequent fires. These results are consistent with previous research in our study area (Agee and Lolley, 2006;Lyons-Tinsley and Peterson, 2012;Prichard et al., 2020;Prichard and Kennedy, 2014), and elsewhere in western North America (Kalies and Yocom Kent, 2016;Schwilk et al., 2009;Stephens and Moghaddas, 2005), but our sampled area encompasses > 7,000 sampled 30-m areas in the entire reburned landscape (51,919 ha; Table 6), and all 3,086 ha within prescribed fire areas that were subsequently burned by a wildfire, instead of field plots Fig. 5. Two-variable partial dependence surfaces showing probability of high severity fire, as measured by the Relativized Burn Ratio, in areas that were longunburned before the fire. The most important predictor variables was the fire resistance score (FRS) captures community-scale tree species fire resistance traits (x-axis of each panels; Stevens et al., 2020). ...
... These results too are supported by previous research indicating that thinning alone can moderate fire behavior, in our study area (Prichard et al., 2020;Prichard and Kennedy, 2014). But across western North America, the combination of thinning and prescribed fire is most effective at moderating fire behavior and reducing fire severity (Fulé et al., 2012;Kalies and Yocom Kent, 2016;Martinson and Omi, 2013;Prichard et al. 2021, Schwilk et al., 2009. We also found that harvest treatments burned with higher severity than paired controls, which is consistent with previous research showing that harvest operations can increase surface fuel loads when tree limbs and tops are relocated to surface fuel beds, resulting in higher fire severity (Prichard and Kennedy, 2012;Stephens et al., 2009). ...
Author direct link, available until mid-Dec, 2021: https://authors.elsevier.com/a/1d-zm1L%7EGwQxUc
We investigated the relative importance of daily fire weather, landscape position, climate, recent forest and fuels management, and fire history to explaining patterns of remotely-sensed burn severity – as measured by the Relativized Burn Ratio – in 150 fires occurring from 2001 to 2019, which burned conifer forests of northeastern Washington State, USA. Daily fire weather, annual precipitation anomalies, and species’ fire resistance traits were important predictors of wildfire burn severity. In areas burned within the past two to three decades, prior fire decreased the severity of subsequent burns, particularly for the first 16 postfire years. In areas managed before a wildfire, thinning and prescribed burning treatments lowered burn severity relative to untreated controls. Prescribed burning was the most effective treatment at lowering subsequent burn severity, and prescribed burned areas were usually unburned or burned at low severity in subsequent wildfires. Patches that were harvested and planted <10 years before a wildfire burned with slightly higher severity. In areas managed within 5 years after an initial fire, postfire harvest and planting reduced prevalence of stand-replacing fire in reburns. However, overall, postfire management actions after a first wildfire only weakly influenced the severity of subsequent fires. The importance of fire-fire interactions to moderating burn severity establishes the importance of stabilizing feedbacks in active fire regimes, and our results demonstrate how silvicultural treatments can be combined with prescribed fire and wildfires to maintain resilient landscapes.
... • Roller chopping reduces woody shrub cover and density, though herbaceous plant species richness does not always increase as much with this method as it does after a prescribed fire. (Schwilk et al. 2009;Watts et al. 2006). This corroborates that surrogates often reduce structure but provide few immediate ecological benefits. ...
... Finally, in some areas fire may be difficult to use but not completely off the table. In cases where surrogate treatments are used in conjunction with prescribed fire, the results can be quite effective (Menges and Gordon 2010;Schwilk et al. 2009). The combination of fire and herbicides can make up for decades of fire exclusion on a site, converting it to a state close to its former condition in less than 10 years (Outcalt and Brockway 2010). ...
Fire has been a significant part of southeastern American forests for thousands of years. Prescribed fire is an effective method to achieve some land management goals, but sometimes it is not possible to use this tool. Fortunately, there are alternative treatment options that land managers can consider. Although none of these surrogate treatments will produce the same suite of benefits as prescribed fire, they can mimic some of the benefits that prescribed fire creates and are better than applying no treatments. This publication provides an overview for landowners and land managers that want to understand surrogate treatments and the economic and ecological tradeoffs associated with each treatment.
... Fire-scarred trees are particularly vulnerable to subsequent fire damage, as exposed wood and thinner bark can lead to greater cambium damage (Shive et al. 2022). Prescribed fire alone typically does not significantly change overstory conditions (Schwilk et al. 2009, Stephens et al. 2012), but the reduction of surface and ladder fuels (Figs. 3 and 4) through repeated small prescribed fires over decades achieved conditions associated with forest resilience. This outcome is highlighted through the trends in tree density and basal area in the Wawona area. ...
... Local incident management personnel stated that "without the debris removal already completed [along Wawona Road], I do not believe we would have been able to keep fire from crossing the road. " Mechanical thinning treatments primarily manipulate and reduce crown connectivity, tree density, and basal area, forest characteristics that strongly influence crown fire potential and long-range spotting (Schwilk et al. 2009, Stephens et al. 2009), which are components of fire behavior that are highly resistant to control. By requiring fewer firefighters in the grove and along Wawona Road, additional firefighters could be committed to structure protection in Wawona and handline construction in heavily fuel-loaded areas that were important for holding (pers. ...
Background
The Washburn fire started on July 7, 2022 in the lower Mariposa Grove in Yosemite National Park, posing immediate threats to the iconic giant sequoias ( Sequoiadendron giganteum ), critical Pacific fisher ( Pekania pennanti ) habitat, and the community of Wawona. The wildfire quickly gained national attention and the public followed Yosemite’s firefighting efforts closely. In the aftermath of the Washburn fire, we evaluate how decades of fire management and recent roadside thinning in the Park shaped the tactics and outcomes of this wildfire. Fuels reduction and prescribed fire have been at the core of Yosemite’s fire management program since the 1970s and much of this activity has been concentrated in the two areas where firefighting operations were most successful in protecting key resources. We use long-term fire effects monitoring data, airborne light detection and ranging data, and operational perspectives to link together science, management, and fire operations.
Results
Successful initial attack and suppression efforts kept fire out of the Mariposa Grove and the community, where topography and the distribution of heavy fuels largely drove fire behavior throughout the course of the fire. We demonstrate the cumulative effects of decades of fuels treatments in reducing two major drivers of fire behavior – tree density and fuel load – and highlight substantially lower ladder fuels and fire severity in treatment units compared to untreated areas within the Washburn fire footprint.
Conclusions
We show how repeated prescribed fire and fuels treatments can promote forest structure indicative of frequent-fire regimes, moderate extreme fire behavior, improve the ability to protect key resources of concern, and increase human safety in the face of unplanned wildfire. Strategically placed prescribed fire and fuels treatments surrounding the Washburn fire were key considerations in wildfire suppression tactics and were instrumental in protecting the Mariposa Grove.
... longer-term vegetation recovery in ecosystems with prescribed burning and wildfires (e.g., Stephens et al., 2009;Volkova et al., 2019). Consequently, fuel reduction is a key management tool to reduce wildfire impacts in fire-suppressed systems (Schwilk et al., 2009;Stephens et al., 2009). Our results show fuel loads also weigh on postfire decomposition of new fuels. ...
... Similarly, Daniels et al. [58] demonstrated that climatic factors had a particularly pronounced influence on fuel accumulation in single-species forests, especially under changing climatic conditions. Furthermore, Schwilk et al. [59] highlighted significant differences in the response mechanisms of various forest types to climatic and biological factors. These differences emphasize the need for forest management strategies that are tailored to the specific characteristics and ecological dynamics of each forest type. ...
(1) Objective: To improve forest fire prevention, this study provides a reference for forest fire risk assessment in Sichuan Province. (2) Methods: This research focuses on various forest vegetation types in Sichuan Province. Given data from 6848 sample plots, five machine learning models—random forest, extreme gradient boosting (XGBoost), k-nearest neighbors, support vector machine, and stacking ensemble (Stacking)—were employed. Bayesian optimization was utilized for hyperparameter tuning, resulting in machine learning models for predicting forest fuel loads (FLs) across five different vegetation types. (3) Results: The FL model incorporates not only vegetation characteristics but also site conditions and climate data. Feature importance analysis indicated that structural factors (e.g., canopy closure, diameter at breast height, and tree height) dominated in cold broadleaf, subtropical broadleaf, and subtropical mixed forests, while climate factors (e.g., mean annual temperature and temperature seasonality) were more influential in cold coniferous and subtropical coniferous forests. Machine learning-based FL models outperform the multiple stepwise regression model in both fitting ability and prediction accuracy. The XGBoost model performed best for cold coniferous, cold broadleaf, subtropical broadleaf, and subtropical mixed forests, with coefficient of determination (R2) values of 0.79, 0.85, 0.81, and 0.83, respectively. The Stacking model excelled in subtropical coniferous forests, achieving an R2 value of 0.82. (4) Conclusions: This study establishes a theoretical foundation for predicting forest fuel capacity in Sichuan Province. It is recommended that the XGBoost model be applied to predict fuel loads (FLs) in cold coniferous forests, cold broadleaf forests, subtropical broadleaf forests, and subtropical mixed forests, while the Stacking model is suggested for predicting FLs in subtropical coniferous forests. Furthermore, this research offers theoretical support for forest fuel management, forest fire risk assessment, and forest fire prevention and control in Sichuan Province.
... To address this knowledge gap, we leveraged an installation of the National Fire and Fire Surrogate Study in the central Sierra Nevada, California (Schwilk et al., 2009). We used a 20-year dataset collected before and after alternative, repeated fuel treatments to investigate demographics of seedling establishment for six native tree species and to identify the primary factors influencing trends. ...
Fire exclusion over the last two centuries has driven a significant fire deficit in the forests of western North America, leading to widespread changes in the composition and structure of these historically fire‐adapted ecosystems. Fuel treatments have been increasingly applied over the last few decades to mitigate fire hazard, yet it is unclear whether these fuel‐focused treatments restore the fire‐adapted conditions and species that will allow forests to persist into the future. A vital prerequisite of restoring fire‐adaptedness is ongoing establishment of fire‐tolerant tree species, and both the type and reoccurrence of fuel treatments are likely to strongly influence stand trajectories. Here, we leveraged a long‐term study of repeated fuel treatments in a Sierra Nevada mixed‐conifer forest to examine the regeneration response of six native tree species to the repeated application of common fuel treatments: prescribed fire, mechanical, mechanical plus fire, and untreated controls. Our objectives were to (1) quantify differences in forest structure and composition following the repeated application of alternative fuel treatments that may influence the establishment environment and then (2) identify the stand structure and climate conditions influencing seedling dynamics. We found that both treatment type and intensity are highly influential in shifting forests toward more fire‐adapted conditions and determining species‐specific regeneration dynamics. Specifically, the conifer species tracked here increased in either colonization or persistence potential following repeated applications of fire, indicating fire may be most effective for restoring regeneration conditions broadly across species. Fire alone, however, was not enough to promote fire‐adapted composition, with concurrent mechanical treatments creating more favorable conditions for promoting colonization and increasing abundances of fire‐tolerant ponderosa pine. Yet, even with repeated fuel treatment application, establishment of fire‐intolerant species far exceeded that of fire‐tolerant species over this 20‐year study period. Moreover, increasing growing season water stress negatively impacted seedling dynamics across all species regardless of treatment type and intensity, an important consideration for ongoing management under heightened climatic stress. While repeated treatments are waypoints in restoring fire‐adapted conditions, more intense treatments via gap‐creation or hotter prescribed fires targeting removal of fire‐intolerant species will be necessary to sustain recruitment of fire‐tolerant species.
... Variation in the effects of thinning and burning treatments on drought resistance may be due to differences in local treatment implementation or inter-or intraspecific differences in tree response. Therefore, controlled experiments conducted across biophysical gradients (e.g., Schwilk et al., 2009;Stoddard et al., 2021) are needed to disentangle such effects. ...
The frequency and severity of drought events are predicted to increase due to anthropogenic climate change, with cascading effects across forested ecosystems. Management activities such as forest thinning and prescribed burning, which are often intended to mitigate fire hazard and restore ecosystem processes, may also help promote tree resistance to drought. However, it is unclear whether these treatments remain effective during the most severe drought conditions or whether their impacts differ across environmental gradients. We used tree‐ring data from a system of replicated, long‐term (>20 years) experiments in the southwestern United States to evaluate the effects of forest restoration treatments (i.e., evidence‐based thinning and burning) on annual growth rates (i.e., basal area increment; BAI) of ponderosa pine (Pinus ponderosa), a broadly distributed and heavily managed species in western North America. The study sites were established at the onset of the most extreme drought event in at least 1200 years and span much of the climatic niche of Rocky Mountain ponderosa pine. Across sites, tree‐level BAI increased due to treatment, where trees in treated units grew 133.1% faster than trees in paired, untreated units. Likewise, trees in treated units grew an average of 85.6% faster than their pre‐treatment baseline levels (1985 to ca. 2000), despite warm, dry conditions in the post‐treatment period (ca. 2000–2018). Variation in the local competitive environment promoted variation in BAI, and larger trees were the fastest‐growing individuals, irrespective of treatment. Tree thinning and prescribed fire altered the climatic constraints on growth, decreasing the effects of belowground moisture availability and increasing the effects of atmospheric evaporative demand over multi‐year timescales. Our results illustrate that restoration treatments can enhance tree‐level growth across sites spanning ponderosa pine's climatic niche, even during recent, extreme drought events. However, shifting climatic constraints, combined with predicted increases in evaporative demand in the southwestern United States, suggest that the beneficial effects of such treatments on tree growth may wane over the upcoming decades.
... Thinning alone often does not reduce and can actually increase surface fuels, and therefore needs to be combined with fire in order to reduce the risk of high intensity wildfires , Lydersen et al. 2017); Fire is a keystone ecosystem process that regulates numerous functions in western forests (e.g., nutrient cycling, decomposition, snag creation, carbon retention, seed germination, etc) --and mechanical treatments cannot replace or replicate many of these important ecological effects (Schwilk et al. 2009, Seidl et al. 2016, Keeley & Safford 2016, Silvas-Bellanca 2011); Managed wildfire can be applied to a much larger proportion of the landscape than mechanical treatments, and in many areas, fire alone is often sufficient to create more resilient forest conditions ); Application of managed wildfire is often more ecologically beneficial, efficient and cost-effective than mechanical treatments at achieving forest restoration goals, and is the best way to align forest conditions with current and future climatic conditions (Boisramé et al. 2017. ...
... Fuel management refers to reducing the loadings of live and dead fuel, improving stand conditions, and reducing the forest fire intensity using prescribed burning, mechanical removal, forest tending, and other measures [7]. Chambers found that prescribed burning can reduce fuel in the long term [8], but the risk of plant invasion is higher and prone to disrupting the ecological balance [9]; Stottlemyer found that mechanical removal can reduce the heat released during combustion and reduce the fire intensity by removing coarse and aerial fuel [10,11], but it requires substantial human and material resources [12][13][14]. Fire retardants have been used to change the burning behavior of wildfires, decrease the fire intensity, and slow the fire's advance. José found that flame retardants can reduce the flammability of fuel to a certain extent, but some of them cause negative effects on the environment [15,16]. ...
This paper aimed to provide technical support for fuel management by exploring different strengths of fuel removal on the physical and chemical properties and flammability of Betula platyphylla forests in the wildland–urban interface. After investigating the northeastern region during the forest fire prevention period in May 2023, a typical WUI area was selected, and three different treatment strengths, combined with a control, were set up to carry out indoor and outdoor experiments for 27 weeks. Compared with previous studies, this study mainly investigated and analyzed the dynamic changes in the physical and chemical properties and fuel flammability after different intensities of treatments on a time scale. By processing and analyzing the data, the following results were obtained. Significant differences existed in the fuel loading of different time-lag fuels over time (p < 0.05). The ash and ignition point of 1 h time-lag fuel after different treatment intensities generally increased first and then decreased, and the higher heat value and ash-free calorific value generally decreased first and then increased. The physical and chemical properties of 10 h and 100 h time-lag fuel fluctuated with time, but the overall change was insignificant. The indicator that had the greatest impact on the combustion comprehensive score for different time-lag fuels was fuel loading. The change in the flammability of dead surface fuel with time varied significantly, and different treatment intensities effectively reduced the fuel’s flammability. The reduction effects, presented in descending order, were as follows: medium-strength treatment > low-strength treatment > high-strength treatment > control check. In conclusion, different treatment intensities have significant effects on the flammability of the fuel, and the medium-strength treatment has the best effect. Considering the ecological and economic benefits, adopting the medium-strength treatment for the WUI to regulate the fuel is recommended.
... A plant community, an organized grouping of all the plants in a specific region, functions as a dynamic equilibrium system where individual plants are interconnected and influenced by their synergistic environment [24][25][26]. The spatial arrangement of various plant individuals within the community alters the microclimate conditions for combustion, and the combustion properties of mixed combustibles differ from those of individual components [27,28]. ...
Fire is a prevalent hazard that poses a significant risk to public safety and societal progress. The continuous expansion of densely populated urban areas, exacerbated by global warming and the increasing intensification of urban heat islands, has led to a notable increase in the frequency and severity of fires worldwide. Incorporating measures to withstand different types of calamities has always been a crucial aspect of urban infrastructure. Well-designed plant communities play a pivotal role as a component of green space systems in addressing climate-related challenges, effectively mitigating the occurrence and spread of fires. This study conducted field research on 21 sites in the green belt around Shanghai, China, quantifying tree morphological indexes and coordinate positions. The spatial structure attributes of different plant communities were analyzed by principal component analysis, CRITIC weighting approach, and stepwise regression analysis to build a comprehensive fire resistance prediction model. Through this research, the relationship between community spatial structures and fire resistance was explored. A systematic construction of a prediction model based on community spatial structures for fire resistance was undertaken, and the fire resistance performance could be quickly judged by easily measured tree morphological indexes, providing valuable insights for the dynamic prediction of fire resistance. According to the evaluation and ranking conducted by the prediction model, the Celtis sinensis, Sapindus saponaria, Osmanthus fragrans, Koelreuteria paniculata, and Distylium racemosum + Populus euramericana ‘I-214’ communities exhibited a high level of fire resistance. On the other hand, the Koelreuteria bipinnata + Ligustrum lucidum, Ginkgo biloba + Camphora officinarum + Ligustrum lucidum, and Ligustrum lucidum + Sapindus saponaria communities obtained lower scores and were positioned lower in the ranking. It is emphasized that the integration of monitoring and regulation is essential to ensure the ecological integrity and well-being of green areas in the Wildland–Urban Interface.
... Previous studies in ponderosa pine-dominated mixed-confier forests in the western U.S. have examined the effects of fuel-reduction treatments on structural complexity (e.g.; Korb et al., 2012;Ritter et al., 2022), overstory and understory composition (e.g., Fulé et al., 2002;Schwilk et al., 2009), and tree responses to stand density and competition reduction (e.g., Bernal et al., 2023;Fiedler et al., 2010). However, no study to date has investigated the influence of fuel-reduction treatments on tree species-mixture effects on individual tree performance. ...
... While this experiment was not designed to separate the effects of individual thinning or burning treatments, these questions have been addressed with finer-scale experiments in other areas (e.g. Schwilk et al. 2009). The need to restore more open conditions to uncharacteristically dense forests that have resulted from decades of anthropogenic fire exclusion is a widespread management problem in seasonally dry forests of North America, whereas in many other parts of the world, reforestation due to overharvesting and land conversion is the primary restoration goal (Lamb 2014;Chazdon & Guariguata 2016). ...
Tree thinning and the application of prescribed surface fire are widespread forest restoration strategies used to regain ecological structure and function throughout dry forests of the western United States. Though such treatments are increasingly applied to broad extents, their effects on forest ecosystems are commonly evaluated at individual experimental sites or treatment units rather than large, operational landscapes. We evaluated the responses of forest structure, regeneration, old‐tree mortality, and tree growth to forest restoration for 21 years in a landscape‐scale (2114 ha) experiment in a Ponderosa pine ( Pinus ponderosa )‐Gambel oak ( Quercus gambelii ) forest in northern Arizona, United States. Relative to the start of the experiment in 1996, tree density and basal area (BA) in the treated area were reduced by 56 and 38%, respectively, at the end of the study period compared to the untreated control. Conifer seedling densities generally declined and sprouting hardwoods increased following treatment. Mortality of old oak trees was significantly higher in the treated area compared to the control, likely due to fire‐caused injury during the prescribed burning. Mean annual BA increment of individual trees was 93% higher in the treated area than in the control. Our study provides new information on Ponderosa pine forest responses to restoration treatments at broad spatial scales and under realistic operational conditions. Results from this study can help inform landscape‐scale restoration projects in dry, fire‐dependent forests.
... As has been shown repeatedly in other studies (Schwilk et al. 2009;Schweitzer et al. 2016;Barefoot et al. 2019), prescribed fire alone is not sufficient to restore and maintain Quercus-Pinus mixedwoods in forests that have not been man-aged for decades. Silvicultural prescriptions designed to reduce the fuelbed, increase understory light availability, and create microsite variability may be most suited for Pinus regeneration. ...
To enhance forest resilience to predicted increases in forest stressors, managers increasingly desire ecologically based restoration approaches that increase ecosystem adaptation potential. Mixedwood stands, which contain a range of life history and functional traits, may be more resistant and resilient to ecosystem stressors. Management of Quercus–Pinus mixedwood stands includes the use of prescribed fire, which requires an understanding of vegetation-fuels-fire feedbacks in these ecosystems. However, a paucity of knowledge exists on the intra-stand spatial patterns of fire effects. We analyzed the effects of a newly initiated prescribed fire program on the intra-stand characteristics of understory woody plants and fuelbed composition and loading in a long-unburned Quercus–Pinus mixedwood stand in Tennessee, USA. We sampled vegetation and fuels in two plots, one that experienced two prescribed fires (burned plot), and one fire-excluded plot directly adjacent (unburned plot). On the burned plot, we recorded lower sapling and seedling densities across taxa. Spatial analysis of advance reproduction in the burned plot indicated a combination of patchy fire effects, canopy openings, and high-light understory environments. We documented significant reductions in total fuel mass. The combination of spatial analysis and ordination revealed that prescribed fires homogenized fuel loads within the burned plot.
... A combination of mechanical removal and a prescribed burn can be highly effective in increasing mouse abundance in a forested setting (Greenberg et al. 2006). This is consistent from forest managers finding that both mechanical and prescribed burn treatments have the largest positive effect on species diversity and species richness (Campbell et al. 2007;Schwilk et al. 2009). This can be applied to management of grasslands as the prescribed burn is effective at restoring alvar habitat and the addition of some mechanical removal can provide refugia the mice select in vegetation. ...
Grassland alvar is a rare plant community that occurs throughout North America and northern Europe, and may require control of encroaching vegetation to be maintained or restored. We evaluated the hypothesis that restoration techniques used to restore the alvar ecosystem do not lead to declines in small mammal abundance. More specifically, we used a Before-After Control-Impact (BACI) design to compare how two methods of vegetation control, prescribed burns and mechanical removal, affected small mammal populations. The restoration was conducted beginning in 2019 on Pelee Island, Ontario, Canada. Live trapping of small mammals and associated vegetation sampling were conducted before and after on treatment and control locations. The only small mammal species to be caught during the study was the white-footed mouse (Peromyscus leucopus (Rafinesque, 1818)), which had an observed decrease across all treatment sites and the control site. Generalized linear mixed effects models demonstrated that the main effects of treatment and year best explained mouse abundance at the site level. Interannual variability appeared to explain more variation in mouse abundance than treatment effects. Our study did not provide strong evidence that the vegetation control measures we employed might limit white-footed mouse abundance.
... Key objectives of the national study were to determine the effectiveness of fire and fire surrogate (i.e., mechanical thinning) treatments, alone and in combination, to reduce fire risk and shift forests to more open-structured, resilient, and sustainable conditions (Schwilk et al., 2009). For the Ohio Hills site, a reversal of mesophication was the primary objective, which would be characterized by a suite of changes including reduced dominance of mesophytic trees beneath the canopy, an increase in the abundance of large oak-hickory advance regeneration, fuel beds more conducive to prescribed fire, and a more diverse and productive ground-layer flora. ...
Across much of the eastern United States, oak forests are undergoing mesophication as shade‐tolerant competitors become more abundant and suppress oak regeneration. Given the historical role of anthropogenic surface fires in promoting oak dominance, prescribed fire has become important in efforts to reverse mesophication and sustain oaks. In 2000 we established the Ohio Hills Fire and Fire Surrogate (FFS) study to examine whether repeated prescribed fire (Fire), mechanical partial harvest (Mech), and their combined application (Mech + Fire) reduced the dominance of subcanopy mesophytic competitors, increased the abundance of large oak–hickory advance regeneration, created a more diverse and productive ground‐layer flora, and produced fuel beds more conducive to prescribed fire, reducing the risk of high‐severity wildfire. Here we report on the ~20‐year effects of treatments on vegetation and fuels and examine the support for interactive effects across a topographic‐moisture and energy gradient. In general, we found that Fire and Mech + Fire treatments tended to reverse mesophication while the Mech‐only treatment did not. The moderate and occasionally high‐intensity fires resulted in effects that were ultimately very similar between the two fire treatments but were modulated by topography with increasing fire severity on drier sites. In particular, we found support for an interaction effect between treatment and topography on forest structure and tree regeneration responses. Fire generally reduced mesophytic tree density in the midstory and sapling strata across all site conditions, while leading to substantial gains in the abundance of large oak–hickory advance regeneration on dry and intermediate landscape positions. Fire also promoted ground‐layer diversity and created compositionally distinct communities across all site conditions, primarily through the increased richness of native perennial herbs. However, the fire had limited effects on fine surface fuel loading and increased the loading of large woody fuels, potentially increasing the risk of high‐severity wildfire during drought conditions. We conclude that two decades of repeated fires, with and without mechanical density reduction, significantly shifted the trajectory of mesophication across most of the landscape, particularly on dry and intermediate sites, highlighting the capacity of a periodic fire regime to sustain eastern oak forests and promote plant diversity but modulated by topography.
... Six and Skov (2009) reported short-term bark beetle activity and emphasized the short pulse of activity associated with burning, wherein some tree-killing beetle species responded positively and killed fire-injured trees but successful attacks did not expand to healthy trees. Schwilk et al. (2009) and(McIver et al., 2013) compared vegetation and fuel responses at Lubrecht with results from other sites in the National FFS study. In these short-term multisite syntheses, Lubrecht showed similar responses to other sites in the network; mechanical treatment was most effective at quickly attaining a desirable stand structure and composition but was not a complete surrogate for fire. ...
Fuel and restoration treatments seeking to mitigate the likelihood of uncharacteristic high‐severity wildfires in forests with historically frequent, low‐severity fire regimes are increasingly common, but long‐term treatment effects on fuels, aboveground carbon, plant community structure, ecosystem resilience, and other ecosystem attributes are understudied. We present 20‐year responses to thinning and prescribed burning treatments commonly used in dry, low‐elevation forests of the western United States from a long‐term study site in the Northern Rockies that is part of the National Fire and Fire Surrogate Study. We provide a comprehensive synthesis of short‐term (<4 years) and mid‐term (<14 years) results from previous findings. We then place these results in the context of a mountain pine beetle (MPB; Dendroctonus ponderosae) outbreak that impacted the site 5–10 years post‐treatment and describe 20‐year responses to assess the longevity of restoration and fuel reduction treatments in light of the MPB outbreak. Thinning treatments had persistently lower forest density and higher tree growth, but effects were more pronounced when thinning was combined with prescribed fire. The thinning+prescribed fire treatment had the additional benefit of maintaining the highest proportion of ponderosa pine (Pinus ponderosa) for overstory and regeneration. No differences in understory native plant cover and richness or exotic species cover remained after 20 years, but exotic species richness, while low relative to native species, was still higher in the thinning+prescribed fire treatment than the control. Aboveground live carbon stocks in thinning treatments recovered to near control and prescribed fire treatment levels by 20 years. The prescribed fire treatment and control had higher fuel loads than thinning treatments due to interactions with the MPB outbreak. The MPB‐induced changes to forest structure and fuels increased the fire hazard 20 years post‐treatment in the control and prescribed fire treatment. Should a wildfire occur now, the thinning+prescribed fire treatment would likely have the lowest intensity fire and highest tree survival and stable carbon stocks. Our findings show broad support that thinning and prescribed fire increase ponderosa pine forest resilience to both wildfire and bark beetles for up to 20 years, but efficacy is waning and additional fuel treatments are needed to maintain resilience.
... Removing these trees may require higher intensity burns or multiple burn treatments [12,13]. A single instance of prescribed fire is not likely to restore historic forest structure [14]. Therefore, thinning is necessary before a prescribed fire is conducted. ...
Understanding and quantifying the resilience of forests to disturbances are increasingly important for forest management. Historical fire suppression, logging, and other land uses have increased densities of shade tolerant trees and fuel buildup in the western United States, which has reduced the resilience of these forests to natural disturbances. One way to mitigate this problem is to use fuel treatments such as stand thinning and prescribed burning. In this study, we investigated changes in forest structure in the Lassen and Plumas National Forests of northern California following a large wildfire. We used long-term field data and aerial photos to examine what management techniques can be effectively used to restore a healthy forest structure and increase the resilience of forests to drought and wildfires. Forest resilience was quantitatively modeled using the forest vegetation simulator and analyzed under varied thinning practices and fuel management scenarios. Results showed that trees below 1,219 m in elevation had the least mortality and gained the most biomass. Trees taller than 45.7 m lost the most biomass. We found that thinning basal area to 16.1 m²·hm⁻² resulted in the highest resilience score for California mixed conifer forest stands and thinning to 9.2 m²·hm⁻² resulted in the highest resilience score for Jeffrey pine stands. Structural diversity had a negative relationship with resilience score. Understanding forest structure, forest resilience, and the factors that make trees vulnerable to mortality will allow managers to better plan fuel treatments for these forests.
... The convergence of all size classes of woody fuels among treatments supports previous work that repeated applications of mastication and prescribed fire are needed to reduce woody fuel accumulations and promote resilient forest structure and composition (Knapp et al., 2017, Schwilk et al., 2009. The fuel accumulation from 2008 to 2021 is similar to post-wildfire forests where pre-fire fuel loadings match prefire levels in six to seven years, though duff recovers over longer periods in dry mixed conifer systems (Eskelson andMonleon, 2018, Lutz et al., 2020). ...
... Through long-term adaptation, plants have evolved heritable fire-adapted traits to improve their fire adaptability during long-term adaptation to fire disturbance [44]. Short-term studies (<10 years) have shown that programmed burns have minimal effect on the mortality of canopy trees [45][46][47]. The mortality rate of P. yunnanensis under natural conditions was approximately 0.93% to 1.27%, while under prescribed burns, it was 1.33%, indicating that P. yunnanensis has some fire resistance and that prescribed burns on it are safe. ...
Prescribed burning is a widely used fuel management employed technique to mitigate the risk of forest fires. The Pinus yunnanensis Franch. forest, which is frequently prone to forest fires in southwestern China, serves as a prime example for investigating the effects of prescribed burning on the flammability of surface dead fuel. This research aims to establish a scientific foundation for managing dead fuel in forests, as well as fire prevention and control strategies. Field data was collected from P. yunnanensis forests located in central Yunnan Province in 2021 and 2022. The study implemented a randomized complete block design with two blocks and three treatments: an unburned control (UB), one year after the prescribed burning (PB1a), and three years after the prescribed burning (PB3a). These treatments were evaluated based on three indices: surface dead-bed structure, physicochemical properties, and potential fire behavior parameters. To analyze the stand characteristics of the sample plots, a paired t-test was conducted. The results indicated no significant differences in the stand characteristics of P. yunnanensis following prescribed burning (p > 0.05). Prescribed burning led to a significant decrease in the average surface dead fuel load from 10.24 t/ha to 3.70 t/ha, representing a reduction of 63.87%. Additionally, the average fire−line intensity decreased from 454 kw/m to 190 kw/m, indicating a decrease of 58.15%. Despite prescribed burning, there were no significant changes observed in the physical and chemical properties of dead fuels (p > 0.05). However, the bed structure of dead fuels and fire behavior parameters exhibited a significant reduction compared with the control sample site. The findings of this study provide essential theoretical support for the scientific implementation of prescribed burning programs and the accurate evaluation of ecological and environmental effects post burning.
... Forest fuel reduction through prescribed burning (PB) imitates the natural process that originally occurred, so it can be a substitute to highintensity wildfires (Schwilk et al., 2009), except doing it in a controlled and limited way. Aboriginal Australians have been using controlled burning practices for tens of thousands of years (Bowman, 1998;Gammage, 2013), while Europeans introduced incident response-based wildfire control (Keating and Handmer, 2013;Pyne, 1991). ...
Fires are an important aspect of environmental ecology; however, they are also one of the most widespread destructive forces impacting natural ecosystems as well as property, human health, water and other resources. Urban sprawl is driving the construction of new homes and facilities into fire-vulnerable areas. This growth, combined with a warmer climate, is likely to make the consequences of wildfires more severe. To reduce wildfires and associated risks, a variety of hazard reduction practices are implemented, such as prescribed burning (PB) and mechanical fuel load reduction (MFLR). PB can reduce forest fuel load; however, it has adverse effects on air quality and human health, and should not be applied close to residential areas due to risks of fire escape. On the other hand, MFLR releases less greenhouse gasses and does not impose risks to residential areas. However, it is more expensive to implement. We suggest that environmental, economic and social costs of various mitigation tools should be taken into account when choosing the most appropriate fire mitigation approach and propose a conceptual framework, which can do it. We show that applying GIS methods and life cycle assessment we can produce a more reasonable comparison that can, for example, include the benefits that can be generated by using collected biomass for bioenergy or in timber industries. This framework can assist decision makers to find the optimal combinations of hazard reduction practices for various specific conditions and locations.
... This effect is generally transitory, but varies with the degree of disturbance (Nave et al. 2010). Mechanical treatments to thin forest stands can cause disturbance that leads to additional soil carbon losses through increased erosion (Schwilk et al. 2009, Stephens et al. 2012. Forest harvest also creates emissions from the operation of machinery used to implement forest harvest; these emissions vary widely based upon the size and type of machinery, as well as the specifics of silvicultural treatments (box 3). ...
Forest and grassland ecosystems in the United States play a critical role in the global carbon cycle, and land management activities influence their ability to absorb and sequester carbon. These ecosystems provide a critical regulating function, offsetting about 12 to 19 percent of the Nation’s annual greenhouse gas emissions. Forests and grasslands are managed for many different objectives and a variety of goods and services, including clean water, clean air, biodiversity, wood products, wildlife habitat, food, recreation, and carbon sequestration. Although carbon may be of interest in developing management plans and options, it may not be a primary management objective. The amount of carbon absorbed by, and stored within, a particular ecosystem can be affected by many factors related to land management, including land-use change, management activities, disturbance, the use of harvested wood, and climate. The long-term capacity of forest ecosystems to absorb and sequester carbon depends in large part on their health, productivity, resilience, and ability to adapt to changing conditions. This report describes the role of forest and grassland ecosystems in the carbon cycle and provides information for considering carbon as one of many objectives for land management activities.
... Fuel reduction treatments can reduce wildfire impacts on forests (Agee and Skinner 2005), bolster suppression efforts (Agee et al. 2000), and improve firefighter safety (Moghaddas and Craggs 2007). In high fire hazard forests, the application of thinning treatments followed by prescribed fire can create fire resistant forest structures by reducing stand densities (Stephens et al. 2009), retaining larger-diameter, fire-resistant trees with greater crown base heights (Agee and Skinner 2005), and decreasing surface and ladder fuels (Schwilk et al. 2009;Hood 2010). Mainly, these changes enhance managers' ability to accommodate the effects of wildfire on the landscape and promote overall forest resilience by allowing ecosystems to maintain their basic structure and function amid disturbance and eventually return to similar structure and composition post-disturbance DeRose and Long 2014;Tubbesing et al. 2019;Steel et al. 2021). ...
Background
In California’s mixed-conifer forests, fuel reduction treatments can successfully reduce fire severity, bolster forest resilience, and make lasting changes in forest structure. However, current understanding of the duration of treatment effectiveness is lacking robust empirical evidence. We leveraged data collected from 20-year-old forest monitoring plots within fuel treatments that captured a range of wildfire occurrence (i.e., not burned, burned once, or burned twice) following initial plot establishment and overstory thinning and prescribed fire treatments.
Results
Initial treatments reduced live basal area and retained larger-diameter trees; these effects persisted throughout the 20-year study period. Wildfires maintained low surface and ground fuel loads established by treatments. Treatments also reduced the probability of torching immediately post-treatment and 20 years post initial thinning treatments.
Conclusions
Fuel treatments in conifer-dominated forests can conserve forest structure in the face of wildfire. Additionally, findings support that the effective lifespans of treatments can be extended by wildfire occurrence. Our results suggest that continued application of shaded fuel breaks is not only a sound strategy to ensure forest persistence through wildfire but may also be compatible with restoration objectives aimed at allowing for the use of more ecologically beneficial fire across landscapes.
... Forest fuel reduction through prescribed burning (PB) imitates the natural process that originally occurred, so it can be a substitute to highintensity wildfires (Schwilk et al., 2009), except doing it in a controlled and limited way. Aboriginal Australians have been using controlled burning practices for tens of thousands of years (Bowman, 1998;Gammage, 2013), while Europeans introduced incident response-based wildfire control (Keating and Handmer, 2013;Pyne, 1991). ...
... Studies by McKinley et al. (2011) and Ryan et al. (2010) indicate that reducing the amount of forest harvest can decrease carbon losses to the atmosphere. As stated by Schwilk et al. (2009) and Stephens et al. (2012), forest disturbances can lead to additional soil carbon losses through soil erosion inducement. All F-ratios are based on the residual mean square error a Significant at 0.05% level of significance ...
Mabira Central Forest Reserve (CFR), one of the biggest forest reserves in Uganda, has increasingly undergone encroachments and deforestation. This chapter presents the implications of a range of forest management options for carbon stocks in the Mabira CFR. The effects of forest management options were reviewed by comparing above-ground biomass (AGB), carbon, and soil organic carbon (SOC) in three management zones. The chapter attempts to provide estimates of AGB and carbon stocks (t/ha) of forest (trees) and SOC using sampling techniques and allometric equations. AGB and carbon were obtained from a count of 143 trees, measuring parameters of diameter at breast height (DBH), crown diameter (CW), and height (H) with tree coordinates. It also makes use of the Velle (Estimation of standing stock of woody biomass in areas where little or no baseline data are available. A study based on field measurements in Uganda. Norges Landbrukshoegskole, Ås, 1995) allometric equations developed for Uganda to estimate AGB.
The strict nature reserve management zone was noted to sink the highest volume of carbon of approximately 6,771,092.34 tonnes, as compared to the recreation zone (2,196,467.59 tonnes) and production zone (458,903.57 tonnes). A statistically significant relationship was identified between AGB and carbon. SOC varied with soil depth, with the soil surface of 0–10 cm depth registering the highest mean of 2.78% across all the management zones. Soil depth and land use/cover types also had a statistically significant effect on the percentage of SOC ( P = 0.05). A statistically significant difference at the 95% significance level was also identified between the mean carbon stocks from one level of management zones to another. Recommendations include: demarcating forest boundaries to minimize encroachment, enforcement of forestry policy for sustainable development, promote reforestation, and increase human resources for efficient monitoring of the forest compartments.
... We predicted that vegetation structure would respond to these disturbances. Specifically, we hypothesized that disturbances would be associated with diminished tree cover, and, due to increased light penetration, would be associated with increasing cover of bare ground, grasses, forbs, and, over time, shrubs (Goosem, 2007;Shatford et al., 2007;Schwilk et al., 2009;Stephens et al., 2012;Crotteau et al., 2013;Miller et al., 2014). We also hypothesized that disturbances would reduce soil stability and alter soil chemistry (Kutiel and Shaviv, 1989;Manley et al., 1995;Neff et al., 2005;James et al., 2021). ...
Introduction
Ecological conditions at a given site are driven by factors including resource availability, habitat connectivity, and disturbance history. Land managers can influence disturbance history at a site by harvesting resources, creating transportation pathways, introducing new species, and altering the frequency and severity of events such as fires and floods. As a result, locations with different land management histories have also likely experienced different disturbance trajectories that, over time, are likely to result in different ecological characteristics.
Methods
To understand how the presence of different management histories may shape ecological conditions across large landscapes, we examined plant and soil characteristics at matched sampling points across jurisdictional boundaries within four Protected Area-Centered Ecosystems (PACEs) in the western US. We employed Bayesian modeling to explore 1) the extent to which specific ecological variables are linked to disturbance and jurisdiction both among and within individual PACEs, and 2) whether disturbance evidence differs among jurisdictions within each PACE.
Results
Across all jurisdictions we found that disturbances were associated with ecologically meaningful shifts in percent cover of bare ground, forbs, grass, shrubs, and trees, as well as in tree species richness, soil stability, and total carbon. However, the magnitude of shifts varied by PACE. Within PACEs, there were also meaningful associations between some ecological variables and jurisdiction type; the most consistent of these were in soil stability and soil carbon:nitrogen ratios. Disturbance evidence within each PACE was relatively similar across jurisdictions, with strong differences detected between contrast jurisdictions only for the Lassen Volcanic National Park PACE (LAVO).
Discussion
These findings suggest an interaction between management history and geography, such that ecotones appear to manifest at jurisdictional boundaries within some, but not all, contexts of disturbance and location. Additionally, we detected numerous differences between PACEs in the size of disturbance effects on ecological variables, suggesting that while the interplay between disturbance and management explored here appears influential, there remains a large amount of unexplained variance in these landscapes. As continued global change elevates the importance of large landscape habitat connectivity, unaligned management activities among neighboring jurisdictions are likely to influence existing ecological conditions and connectivity, conservation planning, and desired outcomes.
... The combination of mechanical thinning and prescribed burning appears to be a potential good management approach for fire risk and drought stress mitigation. Previous studies have experimentally proved short-term benefits of combining prescribed burning with thinning in reducing potential fire hazard (Piqué and Domènech, 2018;Schwilk et al., 2009). Hood et al. (2020) reported absence of long-term benefits after treatments in terms of fuel reduction, but they described a long-lasting change in species composition towards less flammable mixtures. ...
Vegetation structure affects the vulnerability of a forest to drought events and wildfires. Management decisions, such as thinning intensity and type of understory treatment, influence competition for water resources and amount of fuel available. While heavy thinning effectively reduces tree water stress and intensity of a crown fire, the duration of these benefits may be limited by a fast growth response of the understory. Our aim was to study the effect of forest structure on pine forests vulnerability to extreme drought events and on the potential wildfire behaviour after management, with a special focus on the role of the understory. In three sub-Mediterranean sites of NE Spain dominated by Pinus nigra, two intensities of thinning (light: aiming at 70-75% canopy cover; and heavy: aiming at 50-60% canopy cover) followed by two understory treatments (mechanical only and mechanical plus prescribed burning) were applied, resulting in four differently managed stands plus an untreated control per site. Four to five years after management, we measured forest structure (overstory in one 314 m 2 circular plot and understory in 20 quadrats of 1 m 2 per treatment unit) and fuel load (in two 10 m transects per treatment unit) and simulated water balance and fire behaviour under extreme weather conditions. Understory contribution was assessed comparing the real structure with a virtual forest stand where understory vegetation equalled the one of the untreated control. Our results suggest that the resulting mid-term structure following treatments effectively reduced water stress and fire behaviour compared with untreated control, and that the most effective treatments were the ones where prescribed burning was applied after light or heavy thinning. While understory clearing contributes to increase the resistance to both disturbances, an additive effect of burning the debris reduced the vulnerability to drought and wildfires after treatments. Our study highlights the importance of managing the understory to further increase forest resistance to both disturbances.
... Given that the shrubs in their experiment were 80-100 years old and as large as 23 cm in diameter, the lack of a greater watershed response suggests that soil moisture pools or canopy tree water use may have increased. The short-lived effects of the shrub removal reported by Johnson and Kovner (1956) suggests that the combination of mechanical, chemical (herbicide) and burning treatments (Schwilk et al., 2009;McIver et al., 2013), similar to those employed in our study, are required to improve forest structure over the long term. ...
Forest disturbance to overstory vegetation can result in increased abundance of understory vegetation, potentially affecting various ecosystem processes. Habitat expansion of a native evergreen woody shrub, Rhododendron maximum (rosebay rhododendron), in southern Appalachian Mountain riparian forests of the eastern United States has occurred following the mortality of Castanea dentata (American chesnut) in the early 20th century and more recently Tsuga canadensis (Eastern hemlock). Increased abundance of R. maximum has been associated with reduced tree seedling recruitment and survival, as well as shorter overstory tree height compared to where R. maximum understory was not present. As part of a larger investigation into the removal of R. maximum to restore vegetation structure and composition, this study examined the effects of removing R. maximum understory (by cutting) and soil O-horizon (by prescribed fire) on microclimate, whole tree and plot-level transpiration during 2016 and 2017 growing seasons. We found increased soil moisture in the wetter year (2017) and greater variation in light transmission to the forest floor after the treatment. Larger trees were able to increase their water use in the drier year (2016), resulting in similar plot-level transpiration of treatment and reference plots. Removal of R. maximum understory is not expected to significantly alter streamflow or stream chemistry during the growing season; however, it can help restore forest structure through improving tree seedling survival and recruitment as well as increasing growth of established trees.
... For example, changing fire regimes drive corresponding shifts in ecosystem carbon and nutrient cycles by changing plant communities, removing plant biomass (both live and dead), direct combustion of soil organic legacies including carbon (C) and nitrogen (N), altering fuel loads, and impacting soil microbial communities (e.g., Baird et al. 1999;Kauffman et al. 1995;Mack et al. 2021;Muqaddas et al. 2015;Ojima et al. 1994;Pellegrini et al. 2015). Drivers that may underlie the responses of fungal communities are complex and likely include (i) direct heatinduced mortality from fire; (ii) abrupt changes to substrates and nutrient availability (Kaye and Hart 1998;Wang et al. 2012); (iii) long-lasting indirect changes in environmental conditions (Chen and Cairney 2002;Reazin et al. 2016); and (iv) altered physiology or mortality of plant hosts on which some fungi depend (Haase and Sackett 1998;Schwilk et al. 2009). Simultaneous shifts in plant responses (from individual plant physiology to entire communities), substrates for fungal decomposers, and soil nutrient availability (including immobilization, losses through combustion and volatilization, and release through organismal mortality) all complicate generalizing fungal fire ecology, particularly across widespread variation in fire regimes and ecosystems. ...
Fires occur in most terrestrial ecosystems where they drive changes in the traits, composition, and diversity of fungal communities. Fires range from rare, stand-replacing wildfires to frequent, prescribed fires used to mimic natural fire regimes. Fire regime factors, including burn severity, fire intensity, and timing, vary widely and likely determine how fungi respond to fires. Despite the importance of fungi to post-fire plant communities and ecosystem functioning, attempts to identify common fungal responses and their major drivers are lacking. This synthesis addresses this knowledge gap and ranges from fire adaptations of specific fungi to succession and assembly fungal communities as they respond to spatially heterogenous burning within the landscape. Fires impact fungi directly and indirectly through their effects on fungal survival, substrate and habitat modifications , changes in environmental conditions, and/or physiological responses of the hosts with which fungi interact. Some specific pyrophilous, or "fire-loving," fungi often appear after fire. Our synthesis explores whether such taxa can be considered cosmopolitan, and whether they are truly fire-adapted or simply opportunists adapted to rapidly occupy substrates and habitats made available by fires. We also discuss the possible inoculum sources of post-fire fungi and explore existing conceptual models and ecological frameworks that may be useful in generalizing fungal fire responses. We conclude with identifying research gaps and areas that may best transform the current knowledge and understanding of fungal responses to fire.
... Thus, a perceived lack of effectiveness for these two approaches may reflect respondents' expertise in fire behavior and forest management; this is confirmed by the finding that "lack of information regarding fuel treatments" is not strongly limiting. In contrast, prescribed burning following tree cutting and livestock grazing were also considered less effective by respondents although they have proven effective in other jurisdictions (Schwilk et al., 2009;Prichard et al., 2021;Rouet-Leduc et al., 2021). These approaches are not common practice for reducing fire risk in BC, so respondents may not be familiar with the effectiveness of these approaches, which can be a barrier to uptake (McGee, 2007;McCaffrey et al., 2013). ...
Wildfires in the wildland-urban interface (WUI) are increasingly threatening lives and livelihoods. These growing impacts have prompted a paradigm shift toward proactive wildfire management that prioritizes prevention and preparedness instead of response. Despite this shift, many communities remain unprepared for wildfires in the WUI due to diverse individual and social-political factors influencing engagement with proactive management approaches. The catastrophic fire seasons of 2017, 2018, and 2021 in British Columbia (BC), Canada, highlighted just how vulnerable communities continue to be and the urgent need to understand the factors limiting engagement to future resilience to wildfire. Our study, conducted prior to the catastrophic fire season in 2017, surveyed 77 community leaders across BC to better understand the factors driving engagement, including risk perception, preferences and support for approaches, and key barriers limiting progress. We demonstrate that wildfire risk is an urgent issue facing communities across BC, but a range of factors drive variable community engagement with proactive wildfire management. First Nations and smaller (≤5,000 residents) communities were less likely to have developed a community wildfire plan, even though First Nations were significantly more concerned than municipalities/regional districts about certain values (such as drinking water and biodiversity) that were at risk from wildfire. In general, proactive approaches that were considered effective were also the most supported. The most highly supported approaches included enforcement of regulations and education, both of which are considered provincial responsibility in BC and are unlikely to alter community values in the WUI. In contrast, approaches involving prescribed burning of the understory had the highest levels of opposition. Despite variability in these individual factors, social-political barriers related to financial and social (time and expertise) capacity primarily limited engagement with proactive wildfire management, including provincial and federal funding programs. However, these barriers are not equally felt across community groups; First Nations identified social capacity (such as expertise on government-sponsored approaches and awareness of funding programs) as significantly more limiting than municipalities/regional districts. Our study illustrates the limitations of implementing a “shared responsibility” of proactive wildfire management in the WUI in BC without targeted supports to address unequal capacity barriers.
... For example, in dry zone forests, a growing body of evidence highlights the effectiveness of forest treatments to alter forest stand structure (Raymond and Peterson 2005, Prichard et al. 2010, 2020, Prichard and Kennedy 2012) and landscape-scale fire spread and severity (Collins et al. 2011, Finney et al. 2008, Ager et al. 2010, Safford 2012, Tubbesing et al. 2019, Hessburg et al. 2021). In addition, stand-level effects of restoration treatments have been monitored on a wide variety of ecosystem resources (Gaines et al. 2007(Gaines et al. , 2010aNorth 2009, McIver et al. 2012 for a review, Moghaddas et al. 2010, Schwilk et al. 2009, Stephens et al. 2009a, 2009b, Stephens and Moghaddas 2005. Based on study findings, there is evidence that properly designed treatments can reduce burned area and wildfire severity and improve forest resilience to climatic changes, but there are tradeoffs in terms of some kinds of wildlife (e.g., spotted owl nesting, roosting) habitats (Barros et al. 2018, Ager et al. 2020. ...
The 1994 Northwest Forest Plan signified a watershed moment for natural resource management on federal lands in the Pacific Northwest. It established clear priorities for ecologically motivated management of terrestrial and aquatic ecosystems and biodiversity conservation on nearly 10 million hectares of public lands in Oregon, Washington, and northern California. Conservation reserves were the primary means of safeguarding remaining old forest and riparian habitats, and the populations of northern spotted owl, marbled murrelet, and Pacific salmon that depend on them. As envisioned, reserves would provide habitat for the protected species during a lengthy recovery period. However, reserve strategies were grounded on two tacit assumptions: the climate is stable, and there are limited disruptions by invasive species; neither of which has turned out to be true. Managing for northern spotted owls and other late-successional and old forest associated species within the context of static reserves has turned out to be incredibly challenging. As climatic and wildfire regimes continually shift and rapidly reshape landscapes and habitats, conservation efforts that rely solely on maintaining static conditions within reserves are likely to fail, especially in seasonally dry forests. Forest planners and managers are now occupied with efforts to amend or revise Forest Plans within the NWFP area. According to the 2012 Planning Rule, their charge is to focus management on restoring ecosystem integrity and resiliency and address impacts of climate change and invasive species. Here, we integrate information from ecological and climate sciences, species recovery planning, and forest plan monitoring to identify management adaptations that can help managers realize the original Plan goals as integrated with the goals of the 2012 Planning Rule. There are no guarantees associated with any future planning scenario; continual learning and adaptation are necessary. Our recommendations include managing for dynamic rather than static conditions in seasonally dry forests, managing dynamically shifting reserves in wetter forests, where dynamics occur more slowly, reducing stressors in aquatic and riparian habitats, and significantly increased use of adaptive management and collaborative planning.
... The other two sites (2A and 2B) were part of the nationwide Fire and Fire Surrogate (FFS) study conducted by the U.S. Forest Service and each included a thinned plot, a thinned-and-burned plot and a control plot. Lowintensity prescribed fire was applied to the thinned-and-burned plots as part of the restoration treatments (Faiella & Bailey, 2007;Schwilk et al., 2009). Prescribed burn methods were consistent across the study sites as all were conducted as part of the FFS project. ...
Thinning of semi‐arid forests to reduce wildfire risk is believed to improve forest health by increasing soil moisture. Increased snowpack, reduced transpiration, and reduced rainfall interception are frequently cited mechanisms by which reduced canopy density may increase soil moisture. However, the relative importance of these factors has not been rigorously evaluated in field studies. We measured snow depth, snow water equivalent, and the spatial and temporal variation in soil moisture at four experimental paired treatment‐control thinning sites in high elevation ponderosa pine forest northern Arizona, USA. We compared snow and soil moisture measurements with forest structure metrics derived from aerial imagery and 3‐dimensional lidar data to determine the relationship between vegetation structure, snow, and soil moisture throughout the annual hydrologic cycle. Soil moisture was consistently and significantly higher in thinned forest plots, even though the treatments were performed 8‐11 years before this study. However, we did not find evidence that snow water equivalent was higher in thinned forests across a range of snow conditions. Regression tree analysis of soil moisture and vegetation structure data provided some evidence that localized differences in transpiration and interception of precipitation influence the spatial pattern of soil moisture at points in the annual hydrologic cycle when the system is becoming increasingly water limited. However, vegetation structure explained a relatively low amount of the spatial variance (R2 < 0.23) in soil moisture. Continuous measurements of soil moisture in depth profiles showed stronger attenuation of soil moisture peaks in thinned sites, suggesting differences in infiltration dynamics may explain the difference in soil moisture between treatments as opposed to overlying vegetation alone. Our results show limited support for commonly cited relationships between vegetation structure, snow, and soil moisture and indicate that future research is needed to understand how reduction in tree density alters soil hydraulic properties. This article is protected by copyright. All rights reserved.
Background
Decades of fire suppression caused drastic changes to community structure and composition across ecosystems, including in Ozark woodlands in Missouri, USA. Reintroducing fire can restore ground flora by reducing midstory tree density, increasing ground layer light, and reducing leaf litter accumulation, but we lack a clear understanding of how these effects vary across time and space. We investigated the effects of repeated prescribed fire on ground flora species richness, floristic quality, abundance, community composition, and stand structure over 20 years in a landscape matrix of dry-mesic woodlands, dry woodlands, and glades using data collected from the Ozark National Scenic Riverways Fire Effects Monitoring program in the Current River Watershed in the Missouri Ozarks.
Results
We found that fire plays a key role in driving community structure and dynamics across community types, although with varying levels of intensity. Herbaceous species richness, abundance, and floristic quality index increased across all community types, while mean coefficient of conservatism decreased. Abundance and floristic quality effects were stronger in drier sites. Community composition changed with successive burns, resulting in several indicator species for post burn treatments. The density of midstory trees declined across community types with repeated fire. The number of burns significantly affected overstory tree density overall, but overstory tree density only declined in dry woodlands and glades and not in dry-mesic woodlands.
Conclusions
Our results suggest that landscape fire shapes plant community structure and dynamics. Specifically, these findings show that fire effects vary among community types and suggest that land managers should consider landscape heterogeneity in fire application for restoration. Separate community types imbedded in the same landscape may respond to fire differently. Understanding repeated fire effects over several decades across multiple community types is critical to informing fire-driven woodland restoration across landscape scales.
Piñon–juniper (PJ) woodlands are a dominant community type across the Intermountain West, comprising over a million acres and experiencing critical effects from increasing wildfire. Large PJ mortality and regeneration failure after catastrophic wildfire have elevated concerns about the long‐term viability of PJ woodlands. Thinning is increasingly used to safeguard forests from fire and in an attempt to increase climate resilience. We have only a limited understanding of how fire and thinning will affect the structure and function of PJ ecosystems. Here, we examined vegetation structure, microclimate conditions, and PJ regeneration dynamics following ~20 years post‐fire and thinning treatments. We found that burned areas had undergone a state shift that did not show signs of returning to their previous state. This shift was characterized by (1) distinct plant community composition dominated by grasses; (2) a lack of PJ recruitment; (3) a decrease in the sizes of interspaces in between plants; (4) lower abundance of late successional biological soil crusts; (5) lower mean and minimum daily soil moisture values; (6) lower minimum daily vapor pressure deficit; and (7) higher photosynthetically active radiation. Thinning created distinct plant communities and served as an intermediate between intact and burned communities. More intensive thinning decreased PJ recruitment and late successional biocrust cover. Our results indicate that fire has the potential to create drier and more stressful microsite conditions, and that, in the absence of active management following fire, there may be shifts to persistent ecological states dominated by grasses. Additionally, more intensive thinning had a larger impact on community structure and recruitment than less intensive thinning, suggesting that careful consideration of goals could help avoid unintended consequences. While our results indicate the vulnerability of PJ ecosystems to fire, they also highlight management actions that could be adapted to create conditions that promote PJ re‐establishment.
Uno studio che ha messo a confronto diversi tipi di trattamento (fuoco prescritto, trinciatura meccanizzata e combinazione di entrambi) per la manutenzione dei viali parafuoco. L’indagine ha stimato il carico e la struttura dei combustibili di superficie in tre anni successivi agli interventi. Attraverso l’uso di tecniche di simulazione sono state valutate le differenze tra i trattamenti nel mitigare il comportamento del potenziale incendio estivo.
The establishment of sustainable, low-intensity fire regimes is a pressing global challenge given escalating risk of wildfire driven by climate change. Globally, colonialism and industrialisation have disrupted traditional fire management, such as Indigenous patch burning and silvo-pastoral practices, leading to substantial build-up of fuel and increased fire risk. The disruption of fire regimes in southeastern Tasmania has led to dense even-aged regrowth in wet forests that are prone to crown fires, and dense Allocasuarina-dominated understoreys in dry forests that burn at high intensities. Here, we investigated the effectiveness of several fire management interventions at reducing fire risk. These interventions involved prescribed burning or mechanical understorey removal techniques. We focused on wet and dry Eucalyptus-dominated sclerophyll forests on the slopes of kunanyi/Mt. Wellington in Hobart, Tasmania, Australia. We modelled potential fire behaviour in these treated wet and dry forests using fire behaviour equations based on measurements of fuel load, vegetation structure, understorey microclimate and regional meteorological data. We found that (a) fuel treatments were effective in wet and dry forests in reducing fuel load, though each targeted different layers, (b) both mechanical treatments and prescribed burning resulted in slightly drier, and hence more fire prone understorey microclimate, and (c) all treatments reduced predicted subsequent fire severity by roughly 2-4 fold. Our results highlight the importance of reducing fuel loads, even though fuel treatments make forest microclimates drier, and hence fuel more flammable. Our finding of the effectiveness of mechanical treatments in lowering fire risk enables managers to reduce fuels without the risk of uncontrolled fires and smoke pollution that is associated with prescribed burning. Understanding the economic and ecological costs and benefits of mechanic treatment compared to prescribed burning requires further research.
Prescribed fires are an important management tool for reducing fuels and returning fire to the landscape. However, rarely are changes in fuels fully quantified using pre- to post-prescribed fire measurements and those studies that do exist show variable results. In the southern Rockies, little literature exists on the impacts of prescribed fires; thus we examined multiple prescribed fires in northern Colorado to understand fire effects and changes in fuel complexes. Most prominently, prescribed fires influenced litter, duff, and rotten coarse woody debris but did not influence other surface fuels. Canopy base height increased and tree density decreased, while basal area was relatively unimpacted. Season of burning impacted fire effects as substrate burn severity, bole char, and crown volume scorch were highest in summer and fall. Continued monitoring of prescribed fires is critical to understand the influence of prescribed fire on wildfires and ultimately improve prescribed fire outcomes.
Entender cómo la gestión forestal afecta a la resistencia de los bosques a múltiples perturbaciones es esencial para garantizar el cumplimento de los objetivos silvícolas. Muchas perturbaciones naturales, como sequías e incendios, a menudo suceden a la par y su impacto depende en gran medida de la estructura y composición del bosque, así como de la calidad de estación. En este estudio nos centramos en el efecto que tienen diferentes tipos de tratamientos selvícolas sobre la resistencia a medio plazo del pino laricio (Pinus nigra) a episodios de sequía e incendios. En 2015 y 2016 se realizaron claras por lo bajo de distinta intensidad (baja y alta), seguidas de dos tipos de gestión del sotobosque (desbroce y tratamiento mecánico o quema de restos) en tres localidades submediterráneas (Solsonès, Cataluña), resultando en cuatro rodales gestionados y un rodal control por localidad. Las simulaciones de balance hídrico y de comportamiento de un incendio sugieren que la reducción del sotobosque mediante quemas de restos en ambas intensidades de clara es el tratamiento que más resistencia confiere al bosque, mientras que la dendrocronología indica que los pinos dominantes incrementan su producción.
The social barriers and opportunities of prescribed fire management practices in the mid-Atlantic region are unknown. We hypothesized that there are mismatches between community perceptions of prescribed fire operations in the mid-Atlantic U.S. and the realities of its current and potential use in landscape management, but that these mismatches varied across the region between places with recent (Pennsylvania (PA)) and long-term (New Jersey (NJ)) active management programs. We used interdisciplinary, mixed-method approaches including trailhead surveys, focus groups, field measurements, simulation modeling, and environmental cost-benefit analysis. The goal was to triangulate the interactions among fire effects on ecosystems, community perceptions of benefits and concerns about prescribed fire, and manager perceptions of barriers and opportunities for putting managed fire safely back on the landscape.
Prescribed fire in dry coniferous forests of the western U.S. is used to reduce fire hazards. How large, old trees respond to these treatments is an important management consideration. Growth is a key indicator of residual tree condition, which can be predictive of mortality and response to future disturbance. Using a combination of long-term plot records and dendrochronological samples, we analyzed the effects of prescribed fire treatments from the early 1990 s on forest structure and individual tree growth in mixed-conifer forests of Lassen Volcanic National Park in northern California. Prescribed fire reduced stand live tree basal area and stem density at our sites up to 10 years following fire. Within two prescribed fire burn units and two adjacent unburned stands, we analyzed tree cores from 136 large (mean stem diameter > 70 cm) yellow pine (Pinus jeffreyi and P. ponderosa) and 136 large (mean stem diameter > 50 cm) white fir (Abies concolor). After accounting for annual precipitation, basal area increment for individual trees initially declined up to < 3 years post-fire for white fir and > 10 years post-fire for yellow pine, presumably in response to tree injuries. Growth improved for both species at a site that was burned twice, particularly for white fir. Recent average basal area increment was positively related to crown ratio and negatively associated with an index of local competition. Our findings suggest that forest management, such as prescribed fire and mechanical thinning, may be beneficial in terms of maintaining or improving tree growth among large residual trees. However, managers may want to balance the benefits of these treatments against inadvertent injury and mortality of large trees.
Emulation silviculture is the use of silvicultural techniques that try to imitate natural disturbances such as wildfire. Emulation silviculture is becoming increasingly popular in Canada because it may help circumvent the political and environmental difficulties associated with intensive forest harvesting practices. In this review we summarize empirical evidence that illustrates disparities between forest harvesting and wildfire. As a rule, harvesting and wildfire affect biodiversity in different ways, which vary a great deal among ecosystem types, harvesting practices, and scale of disturbance. The scales of disturbance are different in that patch sizes created by logging are a small subset of the range of those of wildfire. In particular, typical forestry does not result in the large numbers of small disturbances and the small number of extremely large disturbances created by wildfires. Moreover, the frequency of timber harvesting is generally different from typical fire return intervals. The latter varies widely, with stand-replacing fires occurring in the range of 20 to 500 years in Canada. In contrast, harvest frequencies are dictated primarily by the rotational age at merchantable size, which typically ranges from 40 to 100 years. Forest harvesting does not maintain the natural stand-age distributions associated with wildfire in many regions, especially in the oldest age classes. The occurrence of fire on the landscape is largely a function of stand age and flammability, slope, aspect, valley orientation, and the location of a timely ignition event. These factors result in a complex mosaic of stand types and ages on the landscape. Timber harvesting does not generally emulate these ecological influences. The shape of cut blocks does not follow the general ellipse pattern of wind driven fires, nor do harvested stands have the ragged edges and unburned patches typically found in stand-replacing fires. Wildfire also leaves large numbers of snags and abundant coarse woody debris, while some types of harvesting typically leave few standing trees and not much large debris. Successional pathways following logging and fire often differ. Harvesting tends to favor angiosperm trees and results in less dominance by conifers. Also, understory species richness and cover do not always recover to the pre-harvest condition during the rotation periods used in typical logging, especially in eastern Canada and in old-growth forests. As well, animal species that depend on conifers or old-growth forests are affected negatively by forest harvesting in ways that may not occur after wildfire. The road networks developed for timber extraction cause erosion, reduce the areas available for reforestation, fragment the landscape for some species and ecological functions, and allow easier access by humans, whereas there is no such equivalency in a fire-disturbed forest.
Recent increases in Pinus ponderosa Dougl. ex Laws. forest density in the southwestern United States have severely reduced understory herbaceous biomass and altered understory species composition. To examine whether changes in graminoid species composition are caused by increased shading, we studied the effects of shade on leaf gas exchange, biomass, and reproductive characteristics of five grass species native to Arizona P. ponderosa forests in a greenhouse study. Blepharoneuron tricholepis (Nash) Torr., Koeleria cristata (L.) Pers., Festuca arizonica Vasey, Muhlenbergia montana (Nutt.) Hitchc., and Sitanion hystrix (Nutt.) J.G. Smith were grown under three light levels representative of photosynthetic photon flux densities and red/far-red ratios that occur beneath P. ponderosa canopies. In general, all species grew better under unshaded conditions, but all survived and flowered even under the dense shade treatment. Reduction of net assimilation rate by shading was the strongest during early reproductive shoot growth for all species except K. cristata, whose assimilation rate was unaffected by shading. Biomass allocation and reproductive responses to shading varied among species. Biomass of S. hystrix was the least affected by shading of all species, and it showed no response in biomass allocation to reproduction but increased height and weight of individual flower stalks under shade. Overall, S. hystrix and K. cristata, species that occur in dense P. ponderosa stands, were least affected by experimental shading, which suggests that shade is a contributing factor to the distribution of grass species in Arizona P. ponderosa forests.
Question: Do rectangular sample plots record more plant species than square plots as suggested by both empirical and theoretical studies? Location: Grasslands, shrublands and forests in the Mediterranean-climate region of California, USA. Methods: We compared three 0.1-ha sampling designs that differed in the shape and dispersion of 1-m 2 and 100-m 2 nested subplots. We duplicated an earlier study that compared the Whittaker sample design, which had square clustered subplots, with the modified Whittaker design, which had dispersed rectangular subplots. To sort out effects of dispersion from shape we used a third design that overlaid square subplots on the modified Whittaker design. Also, using data from published studies we extracted species richness values for 400-m 2 subplots that were either square or 1:4 rectangles partially overlaid on each other from desert scrub in high and low rainfall years, chaparral, sage scrub, oak savanna and coniferous forests with and without fire. Results: We found that earlier empirical reports of more than 30% greater richness with rectangles were due to the confusion of shape effects with spatial effects, coupled with the use of cumulative number of species as the metric for comparison. Average species richness was not significantly different between square and 1:4 rectangular sample plots at either 1-or 100-m 2. Pairwise comparisons showed no significant difference between square and rectangular samples in all but one vegetation type, and that one exhibited significantly greater richness with squares. Our three intensive study sites appear to exhibit some level of self-similarity at the scale of 400 m 2, but, contrary to theoretical expectations, we could not detect plot shape effects on species richness at this scale. Conclusions: At the 0.1-ha scale or lower there is no evidence that plot shape has predictable effects on number of species recorded from sample plots. We hypothesize that for the mediterranean-climate vegetation types studied here, the primary reason that 1:4 rectangles do not sample greater species richness than squares is because species turnover varies along complex environmental gradients that are both parallel and perpendicular to the long axis of rectangular plots. Reports in the literature of much greater species richness recorded for highly elongated rectangular strips than for squares of the same area are not likely to be fair comparisons because of the dramatically different periphery/area ratio, which includes a much greater proportion of species that are using both above and below-ground niche space outside the sample area.
Frequent, low intensity fire was an important component of the natural disturbance regime of presettlement savannas and woodlands in the southeastern USA dominated by longleaf pine (Pinus palustris), and prescribed burning is now a critical part of the management of these endangered habitats. Fire season, fire frequency, and fire intensity are three potentially important, though still little understood, components of both natural and managed fire regimes. In this long-term (8-yr) study, we experimentally (through the use of prescribed burning) tested for effects of fire season (eight different times throughout the year) and fire frequency (annual vs. biennial burning), on population dynamics (recruitment, growth, mortality, change in density, and change in basal area [the total basal area of all stems in a plot]) and species composition of trees in two quite different types of longleaf-pine-dominated habitats (north Florida sandhills and flatwoods). Limited fire temperature and intensity data were also collected during one year to examine the relationship between fire behavior (temperature and intensity) and tree mortality. Contrary to prior hypotheses, our results showed few systematic or predictable effects of season or frequency of burning on dynamics of longleaf pine. Instead, variability in the population dynamics of this species appeared to be related largely to variation in fire behavior, regardless of the season of burning. Consistent with prior hypotheses, we found that deciduous oak species (Quercus laevis, Q. margaretta, and Q. incana) were least vulnerable to dormant-season burning and most vulnerable to burning early in the growing season. This was shown particularly by seasonal trends in the effect of burning on oak mortality (both topkill and complete kill) and, to a lesser extent, on oak recruitment. Oak densities and basal areas also declined in the spring-burned plots, resulting in a shift away from oaks and towards increased dominance by longleaf pine. Detrimental effects of spring burning on oaks were partly explained by fire behavior, but there appeared also to be an important residual effect of burning season, particularly on complete kill. Though longleaf pine population dynamics did not differ markedly as a result of burning season and frequency, we did find important differences in pine dynamics between the two habitats (i.e., sandhills and flatwoods). In general, populations of longleaf pines in the sandhills appeared to be density regulated, while flatwoods pine populations were declining regardless of the level of intraspecific competition. This suggests that long-term persistence of longleaf pine, and perhaps other fire-adapted species in frequently burned longleaf-pine-dominated communities, may be determined by complex interactions between habitat factors and fire regimes.
A conceptual model of fire and forest restoration and maintenance is presented. The process must begin with clearly articulated goals and depends upon derivation of science-driven models that describe the natural or desired conditions. Evaluating the extent to which contemporary landscapes depart from the model is a prerequisite to determining the need for restoration. Model landscapes that include the historical range of variability are commonly used as target conditions in setting restoration objec- tives. Restoration is a corrective step that ultimately must be replaced by a maintenance process. In a world of changing climate, structural targets of historical conditions will become progressively less meaningful to ecosystem maintenance. Future fire manage- ment needs to focus more on fire as a process, in particular as it pertains to proper ecosystem functioning. One area in need of much further research is the critical role of gap formation in forest regeneration. Forests of the Sierra Nevada in California, like other western coniferous forests, have had ecosystem processes greatly disturbed by fire management practices of the 20 th century. This impact has been repeatedly documented through historical studies of fire frequencies revealed in the annual growth rings of fire-scarred trees. These dendrochro- nology studies show a high frequency of fire prior to Euroamerican settlement, with fires in many mid-elevation forest stands occurring at intervals of roughly every 5-25 years (fig. 1). The fact that these estimates are based upon trees that have persisted through repeated fires demon- strates that the pre-Euroamerican fire regime was one of low intensity/severity fires over a significant portion of the landscape. Beginning in the latter half of the 19 th century, fire frequency declined and throughout the 20 th century,
During the late fall of 2002 we administered three burns in mixed conifer forest sites in the north-central Si- erra Nevada. Eight months later we measured fire-induced injury and mortality in 1300 trees. Using logistic regression, an array of crown scorch, stem damage, fuels, and fire-behavior variables were examined for their influence on tree mortality. In Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), white fir (Abies concolor (Gord. & Glend.) Lindl.), and incense cedar (Calocedrus decurrens (Torr.) Florin), smaller trees with greater total crown damage had higher mor- tality rates. Smaller stem diameters and denser canopies predicted mortality best in ponderosa pine (Pinus ponderosa Dougl. ex P. Laws. & C. Laws). Duff consumption and bark char severity increased model discrimination for white fir and incense cedar and California black oak (Quercus kelloggii Newberry), respectively. In tanoak (Lithocarpus densiflorus (Hook. & Arn.) Rehd.), greater total crown damage in shorter trees resulted in higher mortality rates. Along with tree diameter and consumption of large (>7.6 cm diameter at breast height, DBH) rotten downed woody debris, fire inten- sity was a significant predictor of overall tree mortality for all species. Mortality patterns for white fir in relation to crown damage were similar among sites, while those for incense cedar were not, which suggests that species in repli- cated sites responded differently to similar burns. Our results demonstrate actual fire-behavior data incorporated into mortality models, and can be used to design prescribed burns for targeted reduction of tree density in mixed conifer forests.
After nearly a century of fire exclusion in many central and southern Sierra Nevada mixed- conifer forests, dead and down surface fuels have reached high levels without the recurring fires that consume the accumulated organic matter. The effects of prescribed fires used to reduce fuel loads and restore fire have been monitored in Yosemite, Sequoia, and Kings Canyon National Parks for over 30 years. Ten years following prescribed fire treatments in Sequoia and Kings Canyon, mean total fuel loads accumulated to 84 percent of pre -fire levels in ponderosa pine forests, 83 percent in white fir-mixed conifer, and 66 percent in giant sequoia-mixed conifer forests. Thirty-one years after burning, mean fuel load of fine and sound woody fuels increased in ponderosa pine research plots in Yosemite. Most fuel accumulation appeared to occur within the first decade after fire, however the post-fire fuel complex was different than that pre-fire. In areas that have remained unburned, surface fuel accumulation appears to be relatively slow and may indicate that decay rates have approached accumulation rates for the mixed-conifer forest types. This long-term information has important implications for fire management planning, including scheduling fuel hazard reduction and subsequent maintenance treatments.
Decades of fire exclusion have led to hazardous fuel accumulations and the deterioration of fire-dependent ecosystems, particularly in the American West. Managers are striving to return the ecological role of fire to many ecosystems and would benefit from a much better understanding of how forest structure and composition might change if fires were reintroduced. We used a forest gap model, developed for forests in the Sierra Nevada, California, USA, that integrates climate, fire, and forest dynamics to investigate forest response to changes in the fire regime. The model simulates a spatially heterogeneous fuel bed that is responsive to changes in forest condition, making it well suited for examining alternative management approaches for restoring Sierra Nevada forests after a century of fire exclusion. Presuppression forest basal area, species composition, and spatial autocor- relation structure were restored quickly, if simulated disturbances that caused substantial tree mortality were reintroduced. Simulations of harvest induced the highest levels of mortality and, thus, most effectively restored forest structure and composition. However, prescribed fires were just as effective in restoring forest structure and composition if they were sufficiently severe.
Emulation silviculture is the use of silvicultural techniques that try to imitate natural disturbances such as wildfire. Emulation silviculture is becoming increasingly popular in Canada because it may help circumvent the political and environmental difficulties associated with intensive forest harvesting practices. In this review we summarize empirical evidence that illustrates disparities between forest harvesting and wildfire. As a rule, harvesting and wildfire affect biodiversity in different ways, which vary a great deal among ecosystem types, harvesting practices, and scale of disturbance. The scales of disturbance are different in that patch sizes created by logging are a small subset of the range of those of wildfire. In particular, typical forestry does not result in the large numbers of small disturbances and the small number of extremely large disturbances created by wildfires. Moreover, the frequency of timber harvesting is generally different from typical fire return intervals. The latter varies widely, with stand-replacing fires occurring in the range of 20 to 500 years in Canada. In contrast, harvest frequencies are dictated primarily by the rotational age at merchantable size, which typically ranges from 40 to 100 years. Forest harvesting does not maintain the natural stand-age distributions associated with wildfire in many regions, especially in the oldest age classes. The occurrence of fire on the landscape is largely a function of stand age and flammability, slope, aspect, valley orientation, and the location of a timely ignition event. These factors result in a complex mosaic of stand types and ages on the landscape. Timber harvesting does not generally emulate these ecological influences. The shape of cut blocks does not follow the general ellipse pattern of wind driven fires, nor do harvested stands have the ragged edges and unburned patches typically found in stand-replacing fires. Wildfire also leaves large numbers of snags and abundant coarse woody debris, while some types of harvesting typically leave few standing trees and not much large debris. Successional pathways following logging and fire often differ. Harvesting tends to favor angiosperm trees and results in less dominance by conifers. Also, understory species richness and cover do not always recover to the pre-harvest condition during the rotation periods used in typical logging, especially in eastern Canada and in old-growth forests. As well, animal species that depend on conifers or old-growth forests are affected negatively by forest harvesting in ways that may not occur after wildfire. The road networks developed for timber extraction cause erosion, reduce the areas available for reforestation, fragment the landscape for some species and ecological functions, and allow easier access by humans, whereas there is no such equivalency in a fire-disturbed forest. Key words: silviculture, forest management, clearcutting, forest conservation, wildfire, biodiversity.
The objective of this research was to test the hypothesis that water and nutrients, and not light, control understory plant species composition in a Pinus ponderosa forest in northeastern Oregon. The experiment was conducted as a split-plot experimental design with a 2 x 2 factorial analysis. To assess the effects of root competition of overstory trees on understory species composition, 20 plots (4 x 4 m) were trenched approximately 1.0 m in depth, and compared to 24 nontrenched plots. To increase light levels to understory vegetation, trees were thinned from 345 to 148 trees ha-1 in half of each block (2.5 ha) during the winter and early spring of 1986. Canonical discriminant analysis indicated that light accounted for the greatest environmental resource response among the treatments. The number of species (8) that increased in cover and density was 60% greater when tree root competition was reduced in the root-reduction treatment, versus 5 when tree canopy influences were reduced in the canopy-reduction treatment. Simple correlation showed that changes in species composition were significantly (P ≤ 0.05) related to both changes in aboveground attributes (light, midday air temperature, and soil temperature) and belowground attributes (soil water potential, pH, and nitrogen). Competition for limited resources, light, water, and nutrients, does affect understory species composition as evidenced by the response of individual species to increasing availability of these resources. For. Sci. 41(4):864-889.
Pre- and post-burn tree mortality rates, size structure, basal area, and ingrowth were determined for four 1.0 ha mixed conifer forest stands in the Log Creek and Tharp's Creek watersheds of Sequoia National Park. Mean annual mortality between 1986 and 1990 was 0.8% for both watersheds. In the fall of 1990, the Tharp's Creek watershed was treated with a prescribed burn. Between 1991 and 1995, mean annual mortality was 1.4% in the unburned Log Creek watershed and 17.2% in the burned Tharp's Creek watershed. A drought from 1987 to 1992 likely contributed to the mortality increase in the Log Creek watershed. The high mortality in the Tharp's Creek watershed was primarily related to crown scorch from the 1990 fire and was modeled with logistic regression for white fir (Abies concolor [Gord. and Glend.]) and sugar pine (Pinus lambertiana [Dougl.]). From 1989 to 1994, basal area declined an average of 5% per year in the burned Tharp's Creek watershed, compared to average annual increases of less than 1% per year in the unburned Log Creek watershed and in the Tharp's watershed prior to burning. Post-burn size structure was dramatically changed in the Tharp's Creek stands: 75% of trees ≤50 cm and 25% of trees >50 cm were killed by the fire. For. Sci. 44(2):341-355.
The fire suppression policy on public lands during the last century in the United States has resulted in increased fuel loadings, necessitating the use of prescribed fire and mechanical treatments to decrease hazardous fuels and risks of catastrophic wildfire. While these practices are widespread, there is great variability in project costs, making planning difficult. Although previous studies have examined the factors that influence management costs, they have grappled with the lack of consistent and reliable data. We used the FASTRACS (Fuel Analysis, Smoke Tracking, and Report Access Computer System) database from the Pacific Northwest Region of the USDA Forest Service to identify important influences on fuels management costs. Projects conducted in the wildland-urban interface consistently exhibited higher treatment costs for both prescribed fire and mechanical fuels treatments.
Nous avons examiné la richesse et la couverture en herbacées en relation avec la saison et la sévérité des feux, cinq saisons de croissance après des brûlages dirigés. Les données ont été récoltées dans six peuplements forestiers auxquels ont été appliqués au hasard trois traitements : pas de feu, un feu printanier et un feu automnal. Les feux d'automne comportaient significativement plus d'espèces exotiques et indigènes annuelles/bisannuelles (an/bi) et une plus grande couverture de cellesci (6,5 % d'exotiques; 1,7 % d'indigènes) que les feux d'automne ou que les aires n'ayant pas été brûlées. Ces patrons sont probablement dus aux effets indirects associés à la sévérité du feu et à la disponibilité de la ressource plus qu'à l'effet direct du feu associé à la période de brûlage. Les modèles CART ont indiqués que la richesse et la couverture élevées des espèces exotiques et indigènes an/bi étaient associées à des trouées dans l'étage dominant et à des aires brûlées sévèrement, des conditions courantes à la suite d'un feu d'automne. Les espèces exotiques ont peut être plus de succès à exploiter ces environnements. Aucun effet du traitement n'a été trouvé pour les espèces indigènes pérennes. L'emplacement était important pour expliquer les patrons des espèces indigènes pérennes, mais la richesse et la couverture étaient également associées positivement avec des feux de faible sévérité, une plus grande couverture arborescente et des débris ligneux grossiers. Ainsi, les attentes d'une plus grande diversité et abondance de plantes indigènes pérennes à la suite de brûlages dirigés ne sont peut être pas remplies et la propagation d'espèces exotiques peut compromettre les autres attributs de l'écosystème. La restauration dans ces forêts représente donc un défi puisque les brûlages dirigés interagissent avec les conditions environnementales actuelles très différentes des conditions historiques.
As part of a national experiment, the Fire and Fire Surrogate Project, we evaluated the effects of forest thinning on small mammal population densities and total small mammal biomass in ponderosa pine (Pinus ponderosa)–dominated forests at 2 study areas in northern Arizona and northern New Mexico, USA. We also evaluated the effects of wildfire on small mammal population densities and biomass after a wildfire burned a portion of one study area. Our statistical methods consisted of estimation of population densities in combined analyses across space and time, followed by a weighted regression analysis of treatment effects on densities. We hypothesized that habitat change postdisturbance would be the critical determinant of population responses to thinning and wildfire within 1 year of disturbances. Our results largely supported this hypothesis, as we documented predicted positive responses to thinning for deer mice (Peromyscus maniculatus), gray-collared chipmunks (Tamias cinereicollis), and least chipmunks (T. minimus). We also observed predicted positive responses to wildfire for deer mice, although our results did not support predicted negative responses to wildfire for least chipmunks. Total small mammal biomass generally increased following both thinning and wildfire. Our results suggest that fuel reduction treatments will have the largest positive impact on small mammal populations in areas where tree densities are especially high.
Although the majority of fires in the western United States historically occurred during the late summer or early fall when fuels were dry and plants were dormant or nearly so, early-season prescribed burns are often ignited when fuels are still moist and plants are actively growing. The purpose of this study was to determine if burn season influences postfire vegetation recovery. Replicated early-season burn, late-season burn, and unburned control units were established in a mixed conifer forest, and understory vegetation was evaluated before and after treatment. Vegetation generally recovered rapidly after prescribed burning. However, late-season burns resulted in a temporary but significant drop in cover and a decline in species richness at the 1 m 2 scale in the following year. For two of the several taxa that were negatively affected by burning, the reduction in frequency was greater after late-season than early-season burns. Early-season burns may have moderated the effect of fire by consuming less fuel and lessening the amount of soil heating. Our results suggest that, when burned under high fuel loading conditions, many plant species respond more strongly to differences in fire intensity and severity than to timing of the burn relative to stage of plant growth.
Introduction This chapter considers the internal and external processes that affect seedling communities. Internal or endogenous drivers include the density dependence of seedling populations, as well as the relationship of parent to offspring and the competitive relationships affecting seedling populations. There are many external or exogenous drivers, but we will focus on climate, predation, and fire. We will integrate these internal and external drivers of community composition to address the questions: To what extent do seedling recruitment strategies relate to community assembly rules and do these rules dictate the potential combinations of regeneration niches to be found in any given community? This chapter will focus on long-lived woody species because the differences in life history stages and factors affecting them appear much more prominent than in some other growth forms. Internal drivers Communities of regeneration niches Plant recruitment strategies have received a great deal of attention generally to determine the environmental conditions that favor one strategy over another (Chapter 11). Although communities comprise an assemblage of different seedling strategies, relatively little attention has been paid to the community combinations or rules that limit possible combinations. A useful concept for understanding seedling communities is that of safe sites (Harper, 1977), which is a species-specific phenomenon driven by unique aspects of ecology and phylogeny. It is important to recognize the diversity of potential safe sites and how they are distributed in space and time. Also of importance is how species reach safe sites and the role of metapopulations.
Seedlings are highly sensitive to their environment. After seeds, they typically suffer the highest mortality of any life history stage. This book provides a comprehensive exploration of the seedling stage of the plant life cycle. It considers the importance of seedlings in plant communities; environmental factors with special impact on seedlings; the morphological and physiological diversity of seedlings including mycorrhizae; the relationship of the seedling with other life stages; seedling evolution; and seedlings in human altered ecosystems, including deserts, tropical rainforests, and habitat restoration projects. The diversity of seedlings is portrayed by including specialised groups like orchids, bromeliads, and parasitic and carnivorous plants. Discussions of physiology, morphology, evolution and ecology are brought together to focus on how and why seedlings are successful. This important text sets the stage for future research and is valuable to graduate students and researchers in plant ecology, botany, agriculture and conservation.
Forest types within Glacier display markedly disparate structures; those within Yosemite possess similar structures. Two of the 3 Glacier forest types are characterized by pronounced compositional differences small and large size classes. In Yosemite, each forest type has a similar composition in both the small and large size classes. These geographic differences in forest structure and compositional trend are attributed to distinctive fire patterns in each region. In Yosemite, the strength and consistency of summer drought stress favor a surface fire regime in all forest types sampled, promoting uniformity of structure and compositional dynamics among Yosemite forests. In Glacier, site microclimates mitigate or exacerbate occasional dry summers, resulting in a broader spectrum of disturbance regimes among forest types, ranging from frequent surface fires on dry, open flats, through crown fires on intermediate settings, to infrequent fires on mesic, sheltered slopes. The diversity of disturbance regimes promotes heterogeneity of structure and complex patterns of compositional dynamics among Glacier forests. -from Author
A flatwoods longleaf pine wiregrass ecosystem, which regenerated naturally following wildfire in 1942, on the Coastal Plain of southern Georgia was treated over a period of four decades with prescribed fire at annual, biennial and triennial intervals during the winter dormant season. Burning caused substantial changes in the understory plant community, with significant reductions in the foliar cover of Ilex glabra in the shrub layer resulting in corresponding increases in the cover of Vaccinium myrsinites, Sporobolus curtissii, Aristida stricta and Andropogon spp. Understory plant species richness, diversity and evenness also increased as a result of periodic fire. Dormant-season burning decreased the cover of litter on the forest floor and significantly increased the standing biomass of A. stricta, S. curtissii, Andropogon spp., all other grasses and all forbs. Recurrent fire also prevented the development of a vigorous midstory, that impedes understory growth and poses a serious fire hazard to the stand. Overstory trees were largely unaffected by burning. Historical light grazing on the site produced no measurable effects on the plant community. Findings suggest that the biennial burning interval results in declines of I. glabra in the shrub layer and litter cover on the forest floor, leading to the largest increases in understory plant species richness and diversity and the biomass productivity of grasses and forbs. Although flatwoods plant communities evolved in environments characterized by growing-season fires of variable frequency, long-term application of dormant-season fire is also recommended as a useful option for sustaining resource values in this and similar longleaf pine wiregrass ecosystems.
Longleaf pine (Pinus palustris) ecosystems are native to nine states of the southern region of the United States. Longleaf pine can grow on a variety of site types including wet flatwoods and savannas along the Atlantic and Gulf coastal plain, higher droughty sand deposits from the fall line sandhills to the central ridge of Florida (Stout and Marion 1993), and the montane slopes and ridges of Alabama and northwest Georgia up to 600 m elevation (Boyer 1990b). This region has a humid subtropical climate (Bailey 1995). Maximum July temperatures average 29°C to >35°C while minimums during January range from 0°C to 13°C. The mean annual precipitation is 1040–1750 mm and is well distributed through the year. Growing season is comparatively long, ranging from 300+ days in Florida to 220 days at the northern limit of longleaf pine’s range. During the late summer and fall, hurricanes can develop over the Atlantic Ocean, move westward, and impact coastal plain forests. Such tropical storms are a principal large-scale disturbance agent for longleaf pine forests near the seacoast.
Pre-Euro-American settlement forest structure and fire regimes for Jeffrey pine-white fir, red fir-western white pine, and lodgepole pine forests in the Lake Tahoe Basin (California and Nevada, USA) were identified using stand structural analysis and fire scars based on measurements of stumps of trees that were cut in the 19th century. Com- parisons of the presettlement reference with contemporary conditions were then used to determine how and why contemporary conditions deviate from presettlement conditions and to guide ecological restoration. Contemporary forests varied in different ways compared to the presettlement reference. Contemporary Jeffrey pine-white fir forests have more and smaller trees, more basal area, less structural variability, and trees with a more clumped spatial distribution than preset- tlement forests. The mean presettlement fire-return interval for Jeffrey pine-white fir forests was 11.4 yr, and most (.90%) fires burned in the dormant season; no fire was recorded in the study area after 1871. Similar differences were identified in the structural characteristics of contemporary and presettlement red fir-western white pine and lodgepole pine forests. However, 19th-century logging changed the composition of red fir-western white pine forests, and these forests now have more lodgepole pine than red fir or western white pine. Comparison of contemporary forests with the presettlement reference suggests that resto- ration treatments in Jeffrey pine-white fir forests should include: (1) density and basal- area reduction, primarily of smaller diameter trees; (2) reintroduction of frequent fire as a key regulating disturbance process; and (3) increasing structural heterogeneity by shifting clumped tree distributions to a more random pattern. Restoration treatments in red fir- western white pine forests should include: (1) a shift in species composition by a density and basal-area reduction of lodgepole pine; and (2) increasing structural heterogeneity by shifting tree distributions to a more random pattern. In lodgepole pine forests the restoration emphasis should be: (1) a density and basal-area reduction of small-diameter trees; and (2) an increase in structural heterogeneity that shifts tree spatial patterns from clumped to a more random distribution. Reintroduction of fire as a regulating process into high-elevation red fir-western white pine and lodgepole pine forests can be viewed as a longer-term restoration goal. The method for quantifying presettlement reference conditions from stumps complements, or is an alternative to, methods based on dendroecology or repeat photog-
Sampling of 1367 trees was conducted in the Side wildfire (4 May 1996), Bridger-Knoll wildfire (20 June 1996) and Dauber prescribed fire (9 September 1995) in northern Arizona ponderosa pine forests (Pinus ponderosa). Tree mortality was assessed for 3 years after each fire. Three-year post-fire mortality was 32.4% in the Side wildfire, 18.0% in the Dauber prescribed fire, and 13.9% in the Bridger-Knoll wildfire. In the Dauber and Side fires, 95% and 94% of 3-year post-fire mortality occurred by year 2, versus 76% in the Bridger-Knoll wildfire. Compared with trees that lived for 3 years after fire, dead trees in all fires had more crown scorch, crown consumption, bole scorch, ground char, and bark beetle attacks. Logistic regression models were used to provide insight on factors associated with tree mortality after fire. A model,using total crown damage,by fire (scorch + consumption) and bole char severity as independent variables was the best two-variable model for predicting individual tree mortality for all fires. The amount of total crown damage,associated with the onset of tree mortality decreased as bole char severity increased. Models using diameter at breast height (dbh) and crown volume,damage,suggested that tree mortality decreased as dbh increased in the Dauber prescribed fire where trees were smallest, and tree mortality increased as dbh increased in the Side and Bridger-Knoll wildfires where trees were largest. Moreover, a U-shaped dbh–mortality
The application of fire in the southern United States continues to increase in complexity due to urban sprawl, air quality issues and regulatory constraints. Many sites suffer from unnaturally high fuel accumulations due to decades of fire exclusion. The loss of habitat to urbanization and successional changes resulting from the absence of fire increases the importance of restoring and maintaining those remaining acres. The wild-land/urban interface case study we discuss herein includes several fire-adapted plant communities ranging in required fire regime from frequent low-intensity fires to infrequent high-intensity stand replacement fires. This area has experienced extended fire-free periods and includes tightly packed homes in subdivisions developed with no consideration of the potential for wild-land fire. Additional smoke-sensitive areas include schools and heavily travelled highways. Such worst-case scenarios exponentially increase the challenges/risks facing fire managers. This case study thus illustrates many of the complex societal issues and technical challenges facing fire managers when planning and conducting restoration burns in the wild-land/urban interface. In fact, it reinforces the notion that, when burning in the wild-land/urban interface, executing the burn often requires less effort than the planning, co-operation and co-ordination necessary prior to ignition.