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Soil properties play key roles in ecosystem recovery at the landscape scale and are regulated by a complex interplay between abiotic and biotic factors. Our study aimed to identify the potential drivers of post-fire changes in mineral soil in the larch forest of southeastern Siberia. We established a 28-year fire chronosequence with 80 sites over a small region of the Greater Khingan Range. At each site, we measured topographic factors, arboreal variables, and ten physical and chemical attributes of surface mineral soils. We used the hierarchical clustering analysis, distance-based redundancy analysis, variation partitioning analysis, Random Forest analysis, and structural equation modeling to disentangle the drivers for the coupled and decoupled patterns in soil properties. The results showed that time since fire is an ecological predictor that cannot be completely discarded for the soil property prediction model. Wildfires altered the effects of topography and arbors on soil properties. Compared with the unburned area, the soil properties of the burned area were associated more with explanatory variables. Here, altitude was a powerful topographic factor that positively correlated with soil properties, whereas slope position, gradient, and aspect had more negative and less positive effects on soil fertility and exhibited similar patterns, of which slope position and gradient exerted stronger influences than aspect. The importance ranking of average tree size was not significantly changed by fires though its relationship with the soil was obviously changed. In boreal larch forest, wildfires enhance the impact of topography on soil properties while decreasing the impact of arbors on soil properties. Although the arbors are not as critical as topography to the change of soil properties in a few decades after fire, the importance of arbors tends to gradually increase over many years. Consequently, wildfires can cause an on-going shift in the importance and the relative importance of topography and arbors on soil properties in boreal larch forest.

The Daxinganling Region, in Heilongjiang Province, China, has experienced considerable losses to forest resources owing to a recent increase in forest fire frequency. This necessitates the predictions of fire behaviour in this region, which requires assessment of fuel moisture content (FMC) at appropriate space and time intervals. Here, we compare and extrapolate results of vapour-exchange methods for predicting hourly moisture contents of downed wood. The FMC of larch and birch twig fuels was measured at 1-h intervals at different slope positions with respect to meteorological factors. The twigs were categorised based on diameter and degree of decay. The Nelson and Simard methods (which consider equilibrium moisture content and the associated time lag) and direct regression method (which allows direct attainment of the FMC) were used. Both Nelson and Simard methods predicted hourly twig moisture content more accurately than the direct regression method. The Simard method was the most accurate, with the lowest mean absolute error and mean relative error as well as relatively small variation coefficients based on results of the extrapolation analysis. Further, the resulting models applied to needle-leaved and lightly decomposed fuels performed better than for the broad-leaved and badly decomposed fuels on evaluation parameters.

Spot fire increase the difficulty of fire-fighting and threaten public safety, and therefore it is important to study ignition probabilities of fuel bed by different firebrands, in order to understand ignition mechanisms and analyze the formation of spot fires. This will provide an important basis for further study to improve the fire-fighting efficiency and reduce casualties. In this study, the ignition probabilities of larch (Larix gmelinii) fuel beds with different moisture levels and packing ratios by diffreent firebrands, including cones and twigs of different sizes, was investigated. Ignition experiments were conducted at different wind speeds generated by fans. The results show that, regardless of moisture content and packing ratio, ignition probability is zero when there is no wind. Both moisture content and wind speed significantly influence ignition probability, while packing ratio has almost no effect. The maximum moisture content at which firebrand ignition occurred was 50%, and ignition probability increased with wind speed and decreased with moisture content. Cones have the highest ignition probability, followed by large twigs and by small twigs. Ignition probability is also affected by firebrand shapes and sizes that determine their potential heat and contact area to the fuel bed. Two empirical models were established to link ignition probability with fuel properties and wind speed. This study will help clarify the mechanism of spot ignition and reduce corresponding losses.

Background and aimBoreal forests account for one third of terrestrial carbon stock. Wildfires are an important perturbation of this carbon pool, affecting in particular the litter layer. After forest fires, the litter layers may possess shifting chemical property and decomposition dynamics due to the changes in post-fire vegetations succession and abiotic factors.MethodsWe measured water-soluble organic carbon (WSOC) and water-soluble nitrogen (WSN) in the litter layers of Oi and Oe horizons in boreal forests along a gradient of fire history in northeastern China. ResultsWe found that WSOC and WSN concentrations in the Oi layer were higher than those in the Oe layer. The concentrations were markedly altered by fires and showed different responses to the ecological succession. The time since fire had significant positive correlations with WSOC in Oi and Oe layers. The distance-based redundancy analysis and the structural equation model analysis suggested that factors additional to the time since fire also influenced the litter water-soluble matter (WSM) properties. Biotic factors were more strongly correlated with the litter WSM properties in the Oe layer than in the Oi layer. Although biotic factors contributed less than abiotic factors to the WSM properties, they still play significant roles in litter WSM in burned area. ConclusionsOur results show that manipulating biotic factors can be an important management strategy for litter WSM restoration, which can assist the overall ecological restoration in burned forests faced with the increasing danger of wildfires in the changing global climate.

High concentration particulate matter 2.5 released from forest fires, in addition to direct burns and asphyxia, PM2.5 is one of the main pollutants which threaten the safety of forest fire fighter. Therefore, to assess spatial distribution of PM2.5, a simulation study was conducted. Fuel beds with different moisture contents and loads were constructed. 144 times burning experiments were carried out under different wind speeds by using wind tunnel device. PM2.5 particles at different spatial points were collected and calculated. The results show that, in the two of three variables interaction between wind speed, fuel load, and, except fuel moisture content, wind speed and fuel load are positively correlated with the PM2.5 concentrations. From PM2.5 concentration which collected at each point in the horizontal and vertical directions, the overall trend is that PM2.5 concentration increases along the horizontal downwind direction (C and D higer than A and B) and the vertical upward direction (A and C higer than B and D) Based on BP neural network, the spatial distribution model of PM2.5 concentration with single hidden layer was established. The prediction accuracy of modeling samples and validation samples is balanced when hidden layer node is 5. This study will help to make reference for PM2.5 occupational exposure standards, forest fire smoke management and forest fire management in China.

Wildfires and pests are natural disturbance agents in many forest ecosystems that often contribute to ecological succession, nutrient cycling, and forest species composition. Mongolian pine (Pinus sylvestris var. mongolica) is a coniferous species that plays an important role as an ecological barrier, and is widely spread in northern China. Its wood is loose, its branches, leaves, and cones contain a high level of resin and volatile oils that make the species highly flammable and the stands dominated by the species are very vulnerable to fire. Recently, resinosis on boles of Pinus sylvestris became an epidemic in China. To explore the potential effects of pests on fire, we compared the flammability of Mongolian pine barks with or without resinosis on boles using a cone calorimeter and several combustion analyses. We found that the barks from boles with resinosis had a greater oil content than the healthy trees. The study also indicated that the ignition times of the barks from boles with and without resinosis were 6.00 s (±1.73) and 22.67 s (±1.15), respectively, and that the heat release rate curves were parabolic, with peaks 225.19 and 75.27 kW/m2, respectively, for the two bark types. Additionally, because resinosis was on the low- to mid-bole of infested trees, the barks from boles with resinosis tended to be ignited much easier than those without resinosis. This clearly evidenced that pests could affect fire severity and behavior by increasing forest flammability. More information about the role that pests play in the different forest cover types is needed to increase our understanding of fire danger and to develop sound forest management policies.

The Great Xing’an Mountains boreal forests were focused on in the northeastern China. The simulated future climate scenarios of IPCC SRES A2a and B2a for both the baseline period of 1961–1990 and the future scenario periods were downscaled by the Delta Method and the Weather Generator to produce daily weather data. After the verification with local weather and fire data, the Canadian Forest Fire Weather Index System was used to assess the forest fire weather situation under climate change in the study region. An increasing trend of fire weather severity was found over the 21st century in the study region under the both future climate change scenarios, compared to the 1961–1990 baseline period. The annual mean/maximum fire weather index was predicted to rise continuously during 2010–2099, and by the end of the 21st century it is predicted to rise by 22%–52% across much of China’s boreal forest. The significant increases were predicted in the spring from of April to June and in the summer from July to August. In the summer, the fire weather index was predicted to be higher than the current index by as much as 148% by the end of the 21st century. Under the scenarios of SRES A2a and B2a, both the chance of extremely high fire danger occurrence and the number of days of extremely high fire danger occurrence was predicted to increase in the study region. It is anticipated that the number of extremely high fire danger days would increase from 44 days in 1980s to 53–75 days by the end of the 21st century.

Monthly projections of maximum temperature, relative humidity, precipitation, and wind speed were made based on the model of HadCM3 and the climatic change scenarios of IPCC SRES A2a and B2a for the future scenario periods of 2010–2039 (referred to as 2020s), 2040–2069(referred to as 2050s), and 2070–2099(referred to as 2080s). The period 1961–1990 was chosen as the baseline period. The observed and projected weather data were downscaled using delta change methods and historical relationships between weather data, area burned, and the seasonal severity rating (SSR) code of the Canadian Fire Weather Index System were examined. The variations of area burned as influenced by climate change were assessed quantitative and qualitative for the study region, assuming that the fire regimes had the similar responses to the warming climate as during the 20th century. Our results indicated that a linear regression relationship existing between the historical area burned and the mean SSR values with regression coefficient in the significant range of 0.16 to 0.61. It was evident that the increased SSR values could result in more area burned; the area burned in the study region would have an increasing pattern during the 21st century under scenarios A2a and B2a scenarios and the area burned would be doubled. Also, the future area burned would have a strong seasonal pattern that more fires would occur in summer and autumn fire season, especially in summer. The area burned in summer fire season would increase by 1.5 times compared to that in the baseline period in 2080s under A2a scenarios.