Search Results (90)

Mediterranean ecosystems are highly susceptible to wildfires, and shifts in fire patterns pose a threat to biodiversity, soil stability, and overall ecosystem health resilience. Implementing prescribed burning as a management strategy to lower wildfire risk has been proposed, but its ecological impacts in Greece are not well understood. This study examines the relationship between fireline intensity during prescribed burning and plant water potential, as well as its effects on soil properties and plant biodiversity on Chios Island, Greece. Field experiments were carried out in representative ecosystems, where we measured flame length to determine fireline intensity. In addition, we gathered soil samples before and after the prescribed burning and evaluated plant diversity. Measuring leaf water potential gave us a better understanding of how plants respond physiologically to different seasonal and site conditions. Our findings revealed that prescribed burning typically boosted plant diversity after the fire, with Fabaceae and Asteraceae playing a key role in regeneration. However, the soil responses differed from one site to another. Some sites saw a decline in organic carbon and nitrogen, while others showed an increase in exchangeable cations like calcium and magnesium, highlighting the importance of site-specific results. Studies on plant water potential revealed seasonal fluctuations in stress, underscoring the importance of accounting for seasonality in prescribed burn planning. Overall, prescribed burning has the potential to enhance biodiversity and ecosystem recovery, while also reducing fuel loads. These results highlight the importance of ongoing, site-specific monitoring for developing sustainable fire management strategies in Mediterranean ecosystems. Full article

In many hardwood forests, resprouting is a common response to disturbance and basal resprouts may represent a substantial component of the forest understory, especially post-wildfire. Despite this, resprouts are often overlooked in biomass assessments and drivers of resprouting responses in certain species are still unknown. These knowledge gaps are problematic as the contribution of resprouts to understory fuel loads are needed for wildfire risk modeling and effective forest stewardship. Here, we validated the handheld mobile laser scanning (HMLS) of basal resprout volume and field measurements of stem count and clump height as methods to estimate the mass of California Bay Laurel (Umbellularia californica) basal resprouts at Pepperwood and Saddle Mountain Preserves, Sonoma County, California. In addition, we examined the role of tree size and wildfire severity in predicting post-wildfire resprouting response. Both field measurements (clump height and stem count) and remote sensing (HMLS-derived volume) effectively estimated dry mass (total, leaf and wood) of U. californica resprouts, but underestimated dry mass for a large resprout. Tree size was a significant factor determining post-wildfire resprouting response at Pepperwood Preserve, while wildfire severity significantly predicted post-wildfire resprout size at Saddle Mountain. These site differences in post-wildfire basal resprouting predictors may be related to the interactions between fire severity, tree size, tree crown topkill, and carbohydrate mobilization and point to the need for additional demographic and physiological research. Monitoring post-wildfire changes in U. californica will deepen our understanding of resprouting dynamics and help provide insights for effective forest stewardship and wildfire risk assessment in fire-prone northern California forests. Full article

Pinus nigra Arnold, which is naturally widespread in mountainous and Mediterranean ecosystems, is a key species for reforestation due to its ecological and economic value. As climate change and changing fire regimes increase the wildfire risk, understanding its fire resilience has become critical. In this study, the morpho-physiological traits (thickness, roughness, moisture content) and flammability characteristics (ignition, heat release, mass loss, as determined in laboratory flammability tests) of the bark of P. nigra were investigated. The trees were selected based on their age (young vs. old) and fire exposure (burned vs. unburned). The bark thickness was significantly greater in older trees, while the bark moisture content was significantly lower in previously burned trees (p ≤ 0.05). The bark thickness correlated strongly with the ignition time, heat release, and mass loss. These results indicate that the age of the tree primarily affects the bark thickness and time to cambium death, while fire exposure primarily affects the bark moisture content, regardless of age. Understanding that the bark thickness and flammability play a key role in tree survival may aid in the selection of individuals or stand structures better suited to survive in fire-prone conditions and in the strategic planning of burns to reduce fuel loads without exceeding the mortality risk of younger or thinner-barked individuals. Full article

Effective estimation of fuel load is critical for mitigating wildfire risks. Here, we evaluate the performance of mobile laser scanning (MLS) and terrestrial laser scanning (TLS) to estimate fuel loads across multiple vegetation layers. Data were collected in two forest regions: the North Kaibab (NK) Plateau in Arizona and Monroe Mountain (MM) in Utah. We used random forest models to predict vegetation attributes, evaluating the performance of full models and transferred models using R², RMSE, and bias. The MLS consistently outperformed the TLS system, particularly for canopy-related attributes and woody biomass components. However, the TLS system showed potential for capturing canopy structure attributes, while offering advantages like operational simplicity, low equipment demands, and ease of deployment in the field, making it a cost-effective alternative for managers without access to more complex and expensive mobile or airborne systems. Our results show that model transferability between NK and MM is highly variable depending on the fuel attributes. Attributes related to canopy biomass showed better transferability, with small losses in predictive accuracy when models were transferred between the two sites. Conversely, surface fuel attributes showed more significant challenges for model transferability, given the difficulty of laser penetration in the lower vegetation layers. In general, models trained in NK and validated in MM consistently outperformed those trained in MM and transferred to NK. This may suggest that the NK plots captured a broader complexity of vegetation structure and environmental conditions from which models learned better and were able to generalize to MM. This study highlights the potential of ground-based LiDAR technologies in providing detailed information and important insights into fire risk and forest structure. Full article

Implementing nature-based solutions (NbSs) for wildfire risk management and other hazards has been challenging in emerging economies due to the high costs, the lack of immediate returns on investment, and stringent inclusion criteria set by organizations like the IUCN and domain experts. To address these challenges, this exploratory study proposes a new concept: green/blue initiatives. These initiatives represent intermediate steps, encompassing small-scale, community-driven activities that can evolve into recognized NbSs over time. To explore this concept, experiences related to wildfire prevention in the Biobío region of Chile were analyzed through primary and secondary source reviews. The analysis identified three initiatives qualifying as green/blue initiatives: (1) goat grazing in Santa Juana to reduce fuel loads, (2) a restoration prevention farm model in Florida called Faro de Restauración Mahuidanche and (3) the Conservation Landscape Strategy in Nonguén. They were examined in detail using data collected from site visits and interviews. In contrast to Chile’s prevailing wildfire policies, which focus on costly, large-scale fire suppression efforts, these initiatives emphasize the importance of reframing wildfire as a manageable ecological process. Lastly, the challenges and enabling factors for adopting green/blue initiatives are discussed, highlighting their potential to pave the way for future NbS implementation in central Chile. Full article

Selection forestry sustains timber production and stand structural complexity via partial harvesting. However, regeneration initiated by harvesting may function as fuel ladders, providing pathways for fire to reach the forest canopy. We sought potential mitigation approaches by simulating stand growth and potential wildfire behavior over a century in stands dominated by coast redwood (Sequoia sempervirens (Lamb. ex. D. Don) Endl.) on California’s north coast. We used the fire and fuels extension to the forest vegetation simulator (FFE-FVS) to compare group selection (GS) to single-tree selection silviculture with either low-density (LD) or high-density (HD) retention on a 20-year harvest return interval. These three approaches were paired with six options involving vegetation management (i.e., hardwood control or pre-commercial thinning (PCT)) with and without fuels treatments (i.e., prescribed fire or pile burning), or no subsequent vegetation or fuel treatment applied after GS, HD, or LD silviculture. Fuel treatment involving prescribed fire reduced hazardous fuel loading but lowered stand density and hence productivity. Hardwood control followed by prescribed fire mitigated potential wildfire behavior and promoted dominance of merchantable conifers. PCT of small young trees regenerating after selection harvests, followed by piling and burning of these cut trees, sustained timber production while reducing potential wildfire behavior by approximately 40% relative to selection silviculture without vegetation/fuel management, which exhibited the worst potential wildfire behavior. Full article

(1) Stand-replacing fires may threaten the continued stability of mixed conifer forests in the U.S. Southwest. Increasing fire frequency and severity have made post-fire forest recovery trajectories uncertain for many coniferous species, potentially leading to long-term shifts in forest structure and composition. (2) The purpose of this study was to examine post-fire stand dynamics over a 10-year period, using a network of permanent plots established prior to wildfire events across Arizona and New Mexico. We assessed changes in overstory composition, regeneration, and fuel loading across different fire severities. (3) High severity fire caused near-total overstory mortality, with little to no conifer regeneration and abundant sprouting hardwood regeneration. Lower severity fire was more favorable to fire-tolerant conifer species; however, mortality among mature trees was high, and fire-intolerant conifers were either diminished or extirpated completely. (4) In high severity fires, changes in overstory and understory structure and composition may be long-lasting. Additionally, increased fuel loads following high severity fire suggests a heightened risk of reburns, potentially perpetuating ecotype conversion. Our findings highlight the need for active management strategies, including reforestation and fuel reduction treatments, to support forest resilience for mixed conifer ecosystems in the US Southwest and similar forest types in other regions in the face of ongoing climate and fire regime changes. Full article

Wildfires in central-south Chile, consistent with trends observed in other Mediterranean regions, are expected to become more frequent and severe, threatening ecosystems and impacting millions of people. This study aims to enhance wildfire resilience in the central-south regions of Chile through the provision of robust information on current wildfire management practices and comparison with successful alternatives implemented in other fire-prone Mediterranean regions. With this aim, we consulted 55 local stakeholders involved in wildfire management, and alongside a comparative analysis of wildfire statistics and resource allocation in selected Mediterranean regions, we critically assessed different strategies to improve wildfire prevention and management in central-south Chile. The comparative analysis indicated notable economic under-investment for wildfire prevention in Chile. Compared to other Mediterranean countries, Chile is clearly below in terms of investment in forest fire prevention, both in global (public investment) and specific terms ($ ha⁻¹, GDP per capita). The experts consulted included fuel management, governance and community participation, territorial management, landscape planning, socioeconomic evaluation, and education and awareness as key aspects for wildfire prevention. The results of the questionnaire indicated that there was a broad consensus regarding the importance of managing biomass to reduce fuel loads and vegetation continuity, thereby enhancing landscape resilience. Landscape planning and territorial management were also emphasized as critical tools to balance ecological needs with those of local communities, mitigating wildfire risks. Fire-Smart management emerged as a nature-based solution and a promising integrated approach, combining fuel treatments with modeling, simulation, and scenario evaluation based on local and regional environmental data. Additionally, educational and social engagement tools were considered vital for addressing misconceptions and fostering community support. Besides a better integration of rural planning with social demands, this study underscores the urgent need to substantially increase the investment and significance of wildfire prevention measures in central-south Chile, which are key to improving its wildfire resilience. Our work contextualizes the reality of wildfires in central-south Chile and directly contributes to mitigating this growing concern by critically examining successful wildfire resilience strategies from comparable fire-prone regions, complementing ongoing local efforts and offering a practical guide for stakeholders in wildfire management and prevention, with particular relevance to central-south Chile and other regions with similar characteristics. Full article

The Amazon region is becoming more vulnerable to wildfires occurring in the dry season, a crisis amplified by climate change, which affects biomass burning across a wide range of forest environments. In this study, we examined the impact of seasonal fire on greenhouse (GHG) emissions over the study region during the last two decades of the 21st century by integrating calibrated and validated satellite-derived products of estimations of burned biomass area, land cover, vegetation greenness, rainfall, land surface temperature (LST), carbon monoxide (CO), and nitrogen dioxide (NO₂) through geospatial techniques. The results revealed a strong impact of fire activity on GHG emissions, with abrupt changes in CO and NO₂ emission factors between early and middle dry season fires (July–September). Among these seven variables analyzed, we found a positive relationship between the total biomass burned area and fire-derived GHG emission factors (r² = 0.30) due to the complex dynamics of plant moisture and associated CO and NO₂ emissions generated by fire. Nevertheless, other land surface drivers showed the weakest relationships (r²~0.1) with fire-derived GHG emissions due to other factors that drive their regional distribution. Our analysis suggests the importance of continued research on the response of fire season to other land surface characteristics that represent the processes driving fire over the study region such as fuel load, composition, and structure, as well as prevailing weather conditions. These determinants drive fire-related GHG emissions and fire-related carbon cycling relationships and can, therefore, appropriately inform policy fire-abatement guidelines. Full article

Electric power transmission lines both cause and are impacted by wildfires and fuel breaks are crucial to mitigate wildfire hazard along and in conjunction with these infrastructures. Information about fuel dynamics is crucial for planning and maintaining fuel treatments, namely, to define their frequency. We sampled mechanically treated power line corridors representative of wide variation in climate, soil, and plant communities in Portugal and at different times since treatment. Non-destructive methods were used to assess ground cover and height per fuel stratum and the corresponding phytovolumes and fine fuel loads were calculated. Variability in fuel metrics was described by fitting logistic generalized linear models or linearized power functions based on time since disturbance and categorical variables for the effect of regeneration strategy, soil-richness structure, and climate. Time since treatment dominated fuel abundance and recovery was faster in communities of obligate resprouters in comparison with obligate or facultative seeders and in light- versus heavy-textured soils. No apparent effect of local climate was found given the short-lived impact of fuel treatments under the productive regional Mediterranean climate. The results provide a decision-making basis to refine the current treatment periodicity. Mechanical-treatment intervals of 3–5 years or 6–10 years are advised, respectively, for wildfire control and to minimize infrastructure damage. Full article

Seasonally dry mature and old-growth (MOG) forests in the western USA face increasing threats from catastrophic wildfire and drought due to historical fire exclusion and climate change. The Emerald Point forest at Lake Tahoe in the Sierra Nevada of California, one of the last remaining old-growth stands at lake level, is at high risk due to elevated fuels and tree densities. The stand supports huge trees and the highest tree diversity in the Lake Tahoe Basin and protects important raptor habitat. In this study, we simulate forest response to vegetation management and wildfire to assess the impacts of four fuel-reduction scenarios on fire behavior and stand resilience at Emerald Point. Results: Our results demonstrate that restorative forest management can greatly improve an MOG forest’s resistance to catastrophic fire. Thinning to the natural range of variation for density, basal area, and fuel loads, followed by a prescribed burn, was most effective at reducing large-tree mortality, maintaining basal area, and retaining live tree carbon post-wildfire, while reducing secondary impacts. Conclusions: Our findings highlight the value of proactive management in protecting old-growth forests in seasonally dry regions from severe fire events, while also enhancing their ecological integrity and biodiversity. Full article

Fuel load is a crucial input in wildfire behavior models and a key parameter for the assessment of fire severity, fire flame length, and fuel consumption. Therefore, wildfire managers will benefit from accurate predictions of the spatiotemporal distribution of fuel load to inform strategic approaches to mitigate or prevent large-scale wildfires and respond to such incidents. Field surveys for fuel load assessment are labor-intensive, time-consuming, and as such, cannot be repeated frequently across large territories. On the contrary, remote-sensing sensors quantify fuel load in near-real time and at not only local but also regional or global scales. We reviewed the literature of the applications of remote sensing in fuel load estimation over a 12-year period, highlighting the capabilities and limitations of different remote-sensing sensors and technologies. While inherent technological constraints currently hinder optimal fuel load mapping using remote sensing, recent and anticipated developments in remote-sensing technology promise to enhance these capabilities significantly. The integration of remote-sensing technologies, along with derived products and advanced machine-learning algorithms, shows potential for enhancing fuel load predictions. Also, upcoming research initiatives aim to advance current methodologies by combining photogrammetry and uncrewed aerial vehicles (UAVs) to accurately map fuel loads at sub-meter scales. However, challenges persist in securing data for algorithm calibration and validation and in achieving the desired accuracies for surface fuels. Full article

Mediterranean landscapes are shaped by natural disturbances such as herbivory and fire that regulate vegetation structure and fuel loads. As a result of the cessation of traditional agricultural practices, land abandonment is a widespread phenomenon in these landscapes, leading to shrub encroachment and heightened fire hazard. This study reports the effects of grazing by domestic herbivores on vegetation structure in transitional woodland–shrubland systems across three case study areas in Portugal. The effects of low and moderate grazing intensity by cattle and horses on vegetation structure were assessed on three vegetation strata—canopy, shrubs, and grasses—using indicators to evaluate the influence of grazing on both horizontal and vertical vegetation structure. Moderate grazing shaped vertical vegetation structure by reducing shrub and grass height and by browsing and thinning the lower branches, creating a discontinuity between understorey and canopy layers. These effects on vertical fuel continuity are anticipated to limit the upward spread of flames and reduce the potential for crown fires. In contrast, low-intensity grazing showed limited effects on both vertical and horizontal vegetation structure. This work highlights the potential of using domestic herbivores as a tool to manage vegetation structure and its contribution to mitigating local wildfire hazards. Full article

Prescribed burns have recently become a widespread environmental management practice for biodiversity restoration to reduce fuel load, to provide forest fire suppression operational opportunities, to favor plant recruitment or to manage wild species. Prescribed fires were again applied in Doñana National Park (southern Spain) after decades of non-intervention regarding fire use. Here, we assessed their impacts on the soil CO₂ effluxes over two years after burning to test the hypothesis that if the ecosystem is resilient, soil respiration will have a rapid recovery to the conditions previous to the fire. Using soil automated CO₂ flux chambers to continuously measure respiration in burned and unburned sites, we showed that soil respiration varies among seasons but only showed significant differences between burned and unburned plots in the fall season one year after fire, which corresponded with the end of the dry season. Comparing soil respiration values from the burned plots in the three fall seasons studied, soil respiration increased significantly in the fall one year after fire, but decreased in the following fall to the values of the control plots. This study highlights the resilience of soil respiration after prescribed fire, showing the potential benefits of prescribed fire to reduce catastrophic wildfires, especially in protected areas subjected to non-intervention. Full article

Objective: Active fuel management operations, such as thinning, can minimize extreme wildfire conditions while preserving ecosystem services, including maintaining understory vegetation diversity. However, the appropriate thinning intensity for balancing the above two objectives has not been sufficiently studied. Methods: This study was conducted to assess the impact of various thinning intensities (light thinning, LT, 15%; moderate thinning, MT, 35%; heavy thinning, HT, 50%; and control treatment, CK) on fuel characteristics, potential fire behavior, and understory vegetation biodiversity in Platycladus orientalis forest in Beijing using a combination of field measurements and fire behavior simulations (BehavePlus 6.0.0). Results: A significant reduction in surface and canopy fuel loads with increasing thinning intensity, notably reducing CBD to below 0.1 kg/m³ under moderate thinning, effectively prevented the occurrence of active crown fires, even under extreme weather conditions. Additionally, moderate thinning enhanced understory species diversity, yielding the highest species diversity index compared to other treatments. Conclusions: These findings suggest that moderate thinning (35%) offers an optimal balance, substantially reducing the occurrence of active crown fires while promoting biodiversity. Therefore, it is recommended to carry out moderate thinning in the study area. Forest managers can leverage this information to devise technical strategies that simultaneously meet fire prevention objectives and enhance understory vegetation species diversity in areas suitable for thinning-only treatments. Full article