The importance of antecedent vegetation and drought conditions as global drivers of burnt area

The seasonal and longer-term dynamics of fuel accumulation affect fire seasonality and the occurrence of extreme wildfires. Failure to account for their influence may help to explain why state-of-the-art fire models do not simulate the length and timing of the fire season or interannual variability in burnt area well. We investigated the impact of accounting for different timescales of fuel production and accumulation on burnt area using a suite of random forest regression models that included the immediate impact of climate, vegetation, and human influences in a given month and tested the impact of various combinations of antecedent conditions in four productivity-related vegetation indices and in antecedent moisture conditions. Analyses were conducted for the period from 2010 to 2015 inclusive. Inclusion of antecedent vegetation conditions representing fuel build-up led to an improvement of the global, climatological out-of-sample R2 from 0.579 to 0.701, but the inclusion of antecedent vegetation conditions on timescales ≥ 1 year had no impact on simulated burnt area. Current moisture levels were the dominant influence on fuel drying. Additionally, antecedent moisture levels were important for fuel build-up. The models also enabled the visualisation of interactions between variables, such as the importance of antecedent productivity coupled with instantaneous drying. The length of the period which needs to be considered varies across biomes; fuel-limited regions are sensitive to antecedent conditions that determine fuel build-up over longer time periods (∼ 4 months), while moisture-limited regions are more sensitive to current conditions that regulate fuel drying.

Trends in forest fuel accumulation in pine forests of Kyiv Polissya in Ukraine

At present, forest fire research is becoming especially relevant in Ukraine. This study examines patterns of forest fuel accumulation in pine (Pinus sylvestris L.) stands that grow in different soil conditions with different pine stand structure. To estimate the load of forest fuel of different fractions, a combined methodology was used: the weighing method and the FIREMON (fuel load estimation) method. It was found that increase in surface forest fuel loads is not directly proportional to forest stands’ age. Fractional size distribution, capacity and loads of forest fuel depend on several factors, among which the greatest role is played by forestry characteristics of the pine stand. It was determined that in the forest site conditions of type C (fairly rich soils) in Kyiv Polissya, the share of forest litter compared to pine stands that grow in poor soil conditions (A) is smaller, ranging from 41% to 76% of the total forest fuel load. The mass proportion of the duff layer varies from 15% in young forest stands to 43% in mature stands. It was established that changes in forest fuel fractions for 1, 10, 100 and 1000 hours varied insignificantly with age rate. The share of substratum woody debris of 10 and 100 hours was insignificant and depended more on the forestry treatment regime on these sites. The mass proportion of coarse woody debris (1000 hours) was also insignificant, varying from 0% to 5.9% of the total load of surface fuel.

Wiregrass (Aristida beyrichiana) survival and reproduction after fire in a long-unburned pine savanna

Restoring fire regimes is a major goal of biodiversity conservation efforts in fire-prone ecosystems from which fire has been excluded. In the southeastern U.S.A., nearly a century of fire exclusion in pine savannas has led to significant biodiversity declines in one of the most species-rich ecosystems of North America. In these savannas, frequent fires that support biodiversity are driven by vegetation-fire feedbacks. Understory grasses are key components of these feedbacks, fueling the spread of fires that keep tree density low and maintain a high-light environment. When fire is reintroduced to long-unburned sites, however, remnant populations of bunchgrasses might experience high mortality from fuel accumulation during periods of fire exclusion. Our objective was to quantify fire effects on wiregrass (Aristida beyrichiana), a key component of vegetation-fire feedbacks, following 16 years without fire in a dry pine savanna typically considered to burn every 1–3 years. We examined how wiregrass size and fuel (duff depth and presence of pinecones) affected post-fire survival, inflorescence and seed production, and seed germination. Wiregrass exhibited high survival regardless of size or fuels. Probability of flowering and inflorescence number per plant were unaffected by fuel treatments but increased significantly with plant size (p = 0.016). Germination of filled seeds was consistent (29–43%) regardless of fuels, although plants in low duff produced the greatest proportion of filled seeds. The ability of bunchgrasses to persist and reproduce following fire exclusion could jumpstart efforts to reinstate frequent-fire regimes and facilitate biodiversity restoration where remnant bunchgrass populations remain.

Studied on the effect of refueling rate on fuel system refueling based on STAR-CCM+

A model of fuel system which is with ORVR is established based on STAR CCM +, to study the influence of different refueling velocity on the formation of liquid seal in refueling process. The simulation results show that the increase of refueling rate leads to the formation of liquid seal in the process of fuel flow, but it will lead to the deterioration of refueling smoothness. When the refueling rate is 15L/min, there is no liquid seal formed at the bottom of the refueling pipe, because of the small gas resistance formed in the refueling process, and when the refueling flow rate reaches 37L/min, a stable dynamic liquid seal can be formed at the bottom of the refueling pipe but the fuel accumulation at the refueling port has taken place. When the refueling flow rate reaches40L/min and 45L/min, a stable dynamic liquid seal is formed at the bottom of the refueling pipe at 4s, but until 4 seconds, fuel has been submerged in the refueling muzzle. At 10 seconds, the fuel accumulation state is the same as 5 seconds, indicating that the gun PSO had taken happened.

Quantifying the Importance of Antecedent Fuel-Related Vegetation Properties for Burnt Area using Random Forests

The seasonal and longer-term dynamics of fuel accumulation affect fire seasonality and the occurrence of extreme wildfires. Failure to account for their influence may help to explain why state-of-the-art fire models do not simulate the length and timing of the fire season or interannual variability in burnt area well. We investigated the impact of accounting for different timescales of fuel production and accumulation on burnt area using a suite of random forest regression models that included the immediate impact of climate, vegetation, and human influences in a given month, and tested the impact of various combinations of antecedent conditions in four productivity-related vegetation indices and in antecedent moisture conditions. Analyses were conducted for the period from 2010 to 2015 inclusive. We showed that the inclusion of antecedent vegetation conditions on timescales > 1 yr had no impact on burnt area, but inclusion of antecedent vegetation conditions representing fuel build-up led to an improvement of the global, climatological out-of-sample R2 from 0.567 to 0.686. The inclusion of antecedent moisture conditions also improved the simulation of burnt area through its influence on fuel build-up, which is additional to the influence of current moisture levels on fuel drying. The length of the period which needs to be considered to account for fuel build-up varies across biomes; fuel-limited regions are sensitive to antecedent conditions over longer time periods (~4 months) and moisture-limited regions are more sensitive to current conditions.

Burnup Credit Evaluation for BWR Spent Fuel from Full Core Calculations

Due to the challenges of spent fuel accumulation, the nuclear industry is exploring more cost-effective solutions for spent fuel management. The burnup-credit method, in application for storage and transport of the spent fuel, gained traction over recent decades since it can remove the over-conservatism of the “fresh-fuel” approach. The presented research is focused on creating an innovative, best estimate approach of the burnup-credit method for boiling water reactor (BWR) spent fuel based on the results of neutronic/thermal-hydraulic coupled full core simulations. The analysis is performed using a Polaris/DYN3D sequence. Four different shuffling procedures were used to estimate the possible range of the BWR fuel discharged burnup variation. The results showed a strong influence of the shuffling procedure on the final burnup distribution. Moreover, a comparison of the 2D lattice and 3D coupled nodal approaches was conducted for the criticality estimation of single fuel assemblies. The analysis revealed substantial improvement in criticality curves obtained with the full-core model. Finally, it was shown that the benefit from the burnup-credit method is larger in the case of more optimal fuel utilisation-based shuffling procedures. The new approach developed here delivers a promising basis for future industrial optimisation procedures and thus cost optimisation.

Stand breakdown and surface fuel accumulation due to spruce budworm (Choristoneura fumiferana) defoliation in the boreal mixedwood forest of central Canada

Spruce budworm (Choristoneura fumiferana (Clemens)) defoliation has been shown to increase the likelihood of large forest fires in central Canada. However, the time frame of heightened risk based on the duration of spruce budworm defoliation has not yet been quantified. In this article, we document the extent of stand breakdown and surface fuel accumulation after a period of spruce budworm defoliation that occurred between 1972 and 1976. Data on stand characteristics were derived from previous studies at three different locations in the boreal mixedwood forests of central Canada: Aubinadong (B.J. Stocks. 1987. For. Chron. 63: 8–14), Gogama, and Gowganda in Ontario. Stand breakdown was measured using a series of transects set in plots 7 years following aerially mapped defoliation (1977–1983). Results show that during the 4 years following 5 years of defoliation, crown breakage, a typical symptom of defoliation, increased by nearly 200%, and surface fuel increased by 145% from predisturbance levels. The high correlation between crown breakage and surface fuels linked defoliation to fuel buildup. We begin to solve the challenge of measuring fuel structure over the expansive scale of spruce budworm outbreaks by quantifying the relationship among stand breakdown, time since the end of defoliation, and the duration of defoliation so that the expected fuel structure can be modelled from annual defoliation surveys.

Migrating birds rapidly increase constitutive immune function during stopover

Migratory flight is physiologically highly demanding and has been shown to negatively affect multiple parameters of constitutive immune function (CIF), an animal's first line of physiological defence against infections. In between migratory flights, most birds make stopovers, periods during which they accumulate fuel for the next flight(s). Stopovers are also commonly thought of as periods of rest and recovery, but what this encompasses is largely undefined. Here, we show that during stopover, northern wheatears Oenanthe oenanthe, a long-distance migratory bird, can rapidly increase constitutive innate immune function. We caught and temporarily caged birds under ad libitum food conditions at a stopover site in autumn. Within 2 days, most birds significantly increased complement activity and their ability to kill microbes. Changes in immune function were not related to the birds' food intake or extent of fuel accumulation. Our study suggests that stopovers may not only be important to refuel but also to restore immune function. Additionally, the increase in CIF could help migrating birds to deal with novel pathogens they may encounter at stopover sites.

Sustainable Land Management, Wildfire Risk and the Role of Grazing in Mediterranean Urban-Rural Interfaces: A Regional Approach from Greece

Mediterranean regions are likely to be the most vulnerable areas to wildfires in Europe. In this context, land-use change has promoted land abandonment and the consequent accumulation of biomass (fuel) in (progressively less managed) forests and (non-forest) natural land, causing higher fire density and severity, economic damage, and land degradation. The expansion of Wildland-Urban Interfaces (WUIs) further affects fire density by negatively impacting peri-urban farming and livestock density. Assuming the role of grazing in controlling fuel accumulation in forests and non-forest natural land as an indirect measure of wildfire containment around large Mediterranean cities, our work focuses on the role of nomadic livestock, i.e., sheep and goats—the most abundant and traditional farm species in the area. The present study (i) investigates the relationship between fire frequency/extent and livestock decline at the regional level in Greece, (ii) explores changes over time in regional wildfire regimes, comparing Attica, a particularly vulnerable peri-urban region which includes Athens (the Greek capital city), with the rest of the country, and (iii) quantifies trends over time in livestock characteristics (population structure and dynamics) over a sufficiently long time interval (1961–2017) at the same spatial scale, with the aim to document the progressive reduction of nomadic livestock in peri-urban districts. A comprehensive analysis of statistical data, corroborated with a literature review, outlined the relationship between livestock decline over time and changes in specific wildfire characteristics at the regional scale, evidencing peculiar environmental conditions in Attica. In this region, a rapid decline of nomadic livestock was observed compared to in the rest of Greece, leading to a higher wildfire risk. The results of this study suggest that nomadic livestock contributes to sustainable management of peri-urban land, stimulating grazing that may prevent fuel accumulation in fringe woodlands.