Climate changes have led to an increase in fire rates throughout the entire range of larch (Larix sibirica, L. gmelinii, and L. cajanderi). We have tested the hypothesis that natural fires are an important factor that contributes to the functional stability and dominance of larch forests in the continuous permafrost zone. We include satellite imageries, on-ground survey data, dendrochronological measurements, and ecoclimatic variables in our analysis. We find that warming in the 21st century has led to an increase in the intensity and frequency of fires and moderate and extreme (>10 000 ha) burned areas. The maximal burn areas and fire frequency are observed in the northern and southern parts of the permafrost zone, respectively. The frequency of fires and burned areas are inversely exponentially dependent on precipitation, soil and ground cover moisture, and atmospheric drought, and they increase exponentially with an increase in air temperature. In the zone of continuous permafrost, larch successfully regenerates in burned areas (up to 500 000+/ha of seedlings). In the zone of island permafrost (the southern part of the study area), the number of regeneration is 2–3 orders lower, and regeneration is represented mainly by hardwood species. The increasing fire frequency in the south of the larch range contributes to the partial transformation of the forested areas into grass and shrub communities. There is a high probability that larch will retreat from its southern range during the process of continuous permafrost thawing. Gross primary productivity (GPP) in burned areas quickly (3–15 years) recovers to the prefire level. In combination with increasing GPP trends, that indicates that larch forests retain their function as a carbon sink despite the increasing fire rate. Under conditions of an increase in fire rate, the firefighting strategy must be changed. It is necessary to realize (1) the impossibility of the total suppression of fires and (2) the ecological significance of fires in the larch forests in the cryolithozone, in which fires are the most important factor supporting the health and dominance of larch forests. Alongside that, periodic natural fires reduce the likelihood of catastrophic fires. It is necessary to focus firefighting efforts on the areas of the most important social, natural, and economic importance, while controlling burning outside these areas by monitoring methods.

Wildfires and logging play an important role in regulating soil carbon fluxes in forest ecosystems. In Siberia, large areas are disturbed by fires and logging annually. Climate change and increasing anthropogenic pressure have resulted in the expansion of disturbed areas in recent decades. However, few studies have focused on the effects of these disturbances on soil CO2 efflux in the vast Siberian areas. The objective of our research was to evaluate differences in CO2 efflux from soils to the atmosphere between undisturbed sites and sites affected by wildfire and logging in Scots pine forests of southern Siberia. We examined 35 plots (undisturbed forest, burned forest, logged plots, and logged and burned plots) on six study sites in the Angara region and four sites in the Zabaikal region. Soil CO2 efflux was measured using an LI-800 infrared gas analyzer. We found that both fire and logging significantly reduced soil efflux in the first years after a disturbance due to a reduction in vegetation biomass and consumption of the forest floor. We found a substantially lower CO2 efflux in forests burned by high-severity fires (74% less compared to undisturbed forests) than in forests burned by moderate-severity (60% less) and low-severity (37% less) fires. Clearcut logging resulted in 6–60% lower soil CO2 efflux at most study sites, while multiple disturbances (logging and fire) had 48–94% lower efflux. The soil efflux rate increased exponentially with increasing soil temperature in undisturbed Scots pine forests (p < 0.001) and on logged plots (p < 0.03), while an inverse relationship to soil temperature was observed in burned forests (p < 0.03). We also found a positive relationship (R = 0.60–0.83, p < 0.001) between ground cover depth and soil CO2 efflux across all the plots studied. Our results demonstrate the importance of disturbance factors in the assessment of regional and global carbon fluxes. The drastic changes in CO2 flux rates following fire and logging should be incorporated into carbon balance models to improve their reliability in a changing environment.

Throughout the larch range, warming leads to frequent fires and an increase in burned areas. We test the hypothesis that fires are an essential natural factor that reset larch regeneration and support the existence of larch forests. The study area included Larix sibirica and L. gmelinii ranges within the permafrost zone. We used satellite-derived and field data, dendrochronology, and climate variables analysis. We found that warming led to an increase in fire frequency and intensity, mean, and extreme (>10,000 ha) burned areas. The burned area is increasing in the northward direction, while fire frequency is decreasing. The fire rate exponentially increases with decreasing soil moisture and increasing air temperature and air drought. We found a contrasting effect of wildfire on regeneration within continuous permafrost and within the southern lowland boundary of the larch range. In the first case, burnt areas regenerated via abounded larch seedlings (up to 500,000+ per ha), whereas the south burns regenerated mostly via broadleaf species or turned into grass communities. After the fire, vegetation GPP was restored to pre-fire levels within 3–15 years, which may indicate that larch forests continue to serve as carbon stock. At the southern edge of the larch range, an amplified fire rate led to the transformation of larch forests into grass and shrub communities. We suggested that the thawing of continuous permafrost would lead to shrinking larch-dominance in the south. Data obtained indicated that recurrent fires are a prerequisite for larch forests’ successful regeneration and resilience within continuous permafrost. It is therefore not necessary to suppress all fires within the zone of larch dominance. Instead, we must focus fire suppression on areas of high natural, social, and economic importance, permitting fires to burn in vast, larch-dominant permafrost landscapes.

The microbiological and some physicochemical properties of iron-illuvial soddy podburs (Entic Rustic Podzols) under Scots pine forests and gray-humus typical light loamy soils (Umbrisols) under secondary birch forests in central areas of the Zabaikalsky krai were studied. Fires result in a decrease in the sum of exchangeable bases, total nitrogen, and available potassium and phosphorus along with an increase in the C : N ratio in soddy podburs of pine forests; the opposite tendencies are observed after fires in gray-humus soils of birch forests. The humus content in the upper soil horizon decreases only after high-severity fire in the recently burned Scots pine forest and increases in all other sites. A decrease in soil acidity is observed at all burned sites. High-severity fires lead to a significant decrease in the content of microbial biomass and the intensity of basal respiration, as well as to changes in the structure of ecotrophic groups of microorganisms in the upper mineral part of soils to a depth of 10 cm, while low-severity fires mainly affect the duff. The qCO2 coefficient increases 2–5 times in the duff and 1.5–2 times in the humus horizon only after high-severity fires. In the recently burned Scots pine forest, the storage of microbial biomass and microbial production of carbon dioxide significantly decrease to a depth of 10 cm of the mineral soil layer. At the steppe site formed after repeated burning in the Scots pine forest and at the birch forest after high-severity fire, the microbial biomass carbon decreases by 15–20

An assessment of the state of forest lands disturbed by fires, logging and insects in the foothills of the Eastern Sayan Mountains in the forest formations inherent in the study area (Siberian stone pine (Pinus sibirica Du Tour), fir (Abies sibirica Ledeb.), Scots pine (Pinus sylvestris L.), spruce (Picea obovata Ledeb.), larch (Larix sibirica Ledeb.), birch (Betula pendula Roth), aspen (Populus tremula L.)) as well as in forest crops was carried out. The impact of fires, insects, logging, and windfalls was found to result in degradation of the forest health conditions of all forest formations within the boundaries of the foothills of the Eastern Sayan Mountains. Characteristics of natural reforestation on disturbed areas of forest lands were revealed. Unsatisfactory reforestation was observed on most of the disturbed areas of forest lands due to proliferation of the dense grass cover, the formation of a thick duff, the growth of sphagnum (Sphagnum L.) and the occurrence of frequent fires. In cases where there is a sufficient amount of healthy regeneration, natural reforestation occurs by vegetative propagation of soft-leaved low-value tree species (birch and aspen), which, in turn, inhibit the young immature generation of coniferous trees (including forest plantations) due to shading and competition for soil nutrients.

The microbiological and some physico-chemical properties of illuvial-ferruginous soddy-podburs (Entic Rustic Podzols) soils in Scots pine forests and gray-humic typical light loamy soils (Umbrisols) in secondary birch forests of the central regions of the Zabaikal krai have been studied. Fires in soddy-podburs pine forests resulted in decrease in the total exchangeable basis, total nitrogen, mobile forms of potassium and phosphorus, and in increase in the proportion of C : N; while in birch forests, on the contrary, an increase of the mentioned indicators and a narrowing of the C : N proportion in the gray-humic typical soils were observed. The content of humus in the upper soil horizon decreases only in recently burned Scots pine forests after a high-severity fire, while in other sites it increases. A decrease in the soil acidity was observed at all burned sites. High-severity fires lead to a significant decrease in the content of microbial biomass and the intensity of basal respiration, as well as to a change in the structure of ecological and trophic groups of microorganisms in the soils up to a depth of 10 cm of the mineral horizon, while low-severity fires mainly affect the duff. The qCO2 coefficient increased 2–5 times after fires in the duff and 1.5–2 times in the humus horizon only after high-severity fires. In recently burned Scots pine forests, the storage of microbial biomass and microbial production of carbon dioxide significantly decreased up to a depth of 10 cm of the mineral soil layer. In the steppe site formed after the impact of fires in the pine forest, and in the birch forest after a high-severity fire, in the humus horizon the carbon storage of microbial biomass decreased by 15–20%, and the microbial production of CO2 increased by 10–20%, predetermining the predominance of mineralization processes. The considered post-fire transformation of the structural and functional parameters of soil microbiocenosis, as well as a 20–40% decrease in the total carbon storage of microbial biomass in the soils of all sites demonstrate a long recovery period of soils after fires in light coniferous and deciduous forests of the central regions of the Zabaikal krai.

Ground fuel loads and structure in dark-coniferous forests with the dominance of Siberian pine have been studied in the Central Siberian State Nature Biosphere Reserve located in the central-taiga zone of Central Siberia. The impacts of surface fires of various forms and severity on the living ground cover are examined. It is found that fires of low to moderate severity reduce ground fuel loads from 35–49 t/ha to 26–28 t/ha, while fires of moderate to high severity reduce them to 17–18 t/ha. Consumption of down woody debris varies from 3 to 29 t/ha, depending on the prefire fuel characteristics and fire form and severity. Steady fires spreading with the fire danger index PV-1 of 3919 ± 482 result in carbon emissions of 14.0 tC/ha from fires of low to moderate severity and 24.6 tC/ha from fires of moderate to high severity. The lowest carbon emissions (10.1 tC/ha) are noted for fast-moving fires spreading with PV-1 of 1167 ± 386.

Wildfires are one of the main disturbances that impact structure, sustainability, and carbon budget of Siberian forests, as well as infrastructure and human safety. The Zabaikal region in the south of Siberia is characterized by one of the highest levels of fire activity in Russia. We have estimated fire disturbances in the Zabaikal region using both a satellite fire dataset and official fire statistics. Both datasets show a trend of increasing fire activity in the region. According to the satellite fire dataset, from 1996 to 2015 total annual area burned in the Zabaikal region varied from 0.12 to 6.33 M ha with forest area burned accounting for 0.04-5.60 M ha. The highest fire activity was observed in the central and southern parts of the Zabaikal region. About 13% (3.88 M ha) of the total forest area in the Zabaikal region was burned more than once during the 20-yr period of observation, with many sites burned multiple times. Fire disturbance was highest in forests dominated by Scots pine. We have evaluated fire impact on fuel loads, carbon emissions, and tree regeneration on about 150 sites in the light-coniferous (larch or Scots pine dominated) forests of the region. Carbon emissions from fires on repeatedly burned areas were 3-50% of those from previously undisturbed sites. Regeneration density depended on site conditions and fire characteristics. Inadequate regeneration for forest recovery was observed in Scots pine stands on dry nutrient-poor soils as well as on repeatedly-disturbed sites. This regeneration failure is leading to transformation of forests to steppe ecosystems on some sites. We conclude that negative impacts of fire disturbance on forests of the Zabaikal region could be decreased through implementation of fire prevention measures with emphasis on education of local communities as well as construction and maintenance of a fuel break system, first of all, nearby settlements and tree plantations. (C) 2016 Elsevier B.V. All rights reserved.

The fire frequency situation in Zabaykal region from 1964 to 2015 is evaluated and discussed in the paper. The main reasons of decadal increase of fire numbers and the area burned are revealed. The main reasons of high fire frequency and the increase of fire activity in the last decades are shown. The characteristics of the weather conditions in the years of high fire frequency are presented. Fire activity was found to increase not only because of the droughts in the last decades but also due to forest disturbances in Zabaykalsky Krai by illegal logging. Based on the data from 170 sample sites laid out with the use of satellite images, forest inventory data and results of ground sample transects, the impact of the wildfires of different type, form and severity on tree mortality in the light-coniferous forests was estimated, as well as the amount of tree regeneration in the forest areas disturbed by fires, logged sites (both burned and unburned), and sites burned repeatedly was evaluated. Wildfires in the Zabaykal region were found to be strong ecological factor influencing on the probability of existence of many forest ecosystems. In case of further climate warming and repeated fires, the part of the forests may transform to the non forest areas. The steppification of the burned sites in the southern forest-steppe regions and in the low parts of the southern slopes at the border with steppe landscapes as well as desertification in the central parts of the region and swamping of burned sites located in the wet soils are observed. Wind and water soil erosion happens at the large burned sites.

Fires are one of the most significant impacts on forests in Russia. Each year an area of several million hectares is exposed to the forest fires, with a significant increase in the burned area in certain years. In several regions of Russia, especially in the forests of southern Siberia an increase in fire frequency and the duration of the fire season is observed. The forests of Zabaikal region are among the most fire disturbed areas in Russia. In this study we used MODIS 500-m surface reflectance products (MCD43A4) and 1-km active fire product (MOD14A1) over 2000 –2015 to monitor fire disturbed areas in south-west part of Zabaikal region. Joint analysis of vegetation indices (shortwave vegetation index –SWVI) derived from MODIS data and materials of in-situ research allowed us to distinguish areas with successful and poor forest regeneration on fire disturbed territories. The linear trend of the SWVI after the fire event was used to assess the state of forest regeneration. The area with poor regeneration was estimated to be more than 900 thousand hectares. Large areas of the Zabaikal region considered in this were exposed to repeated fires. An analysis of vegetation indices dynamics showed that areas affected by fires 2 times or more during the study period often experienced forest regeneration failure. This study was supported by the Russian Foundation for Basic Research grant 15-04-06567.

Based on the MODIS radiometer data, the level of disturbance of forest lands by fires has been estimated for southwestern areas of the Zabaikal region. A combined analysis of vegetation indices calculated by measuring reflected radiation in the near and mid-infrared wave ranges and the data of on-ground studies allowed us to identify sites with successful and poor reforestation. Based on the instrumental data, it is found that repeated fires prevent successful reforestation. An analysis of seasonal dynamics indicates that summer fires result in greater damages of forest vegetation than those caused by spring fires. Larch stands prevailing in the region cover the largest portion of fire-disturbed lands (and the largest area, where reforestation processes are hampered), while pine and deciduous stands are characterized by a higher frequency of fires.

Fire is the main ecological disturbance controlling forest development in the Russian boreal forests and contributing substantially to the global carbon cycle. The warmer and dryer climate observed recently in the boreal forests is considered to be responsible for extreme fire weather, resulting in higher fire frequency, larger areas burned, and an increase of fire severity (Flannigan et al. 2009). Because of the increase of fire activity, boreal forests in some regions may not be able to reach maturity before they re-burn, which means less carbon will be stored in the ecosystem and more will remain in the atmosphere. Moreover, if one fire occurs within a few years of another, some stands will not re-grow at all, and even more carbon will accumulate in the atmosphere. Southern regions of Siberia are the most vulnerable to climate change and fires (Malevsky-Malevich et al. 2008, Gustafson et al. 2010). Unusually high fire frequency and short fire return interval became characteristics for many regions recently (Kuprianov 2009, Buryak et al. 2011). Zabaikalye region located in the south of Siberia is characterized by one of the highest fire activity in Russia (Kukavskaya et al. 2013). This region corresponds to the “hot spot areas” of land cover change due to increased fire frequency (Achard et al. 2006). The objective of our research was to investigate the impact of repeated fires on carbon emissions and forest ecosystem components in the Zabaikalye region, southern Siberia.

An analytical review of forest fires in the forests of Siberia from literature data published over the past 50 years is given. Prior to 1970 the main attention in publications was given to the investigation of fire nature in the southern taiga and mountain forests of Western and Central Siberia, Altai and Trans-Baikal. From 1971 to 1980, publications were characterized by wider aspects of forest fire research and expansion of the geographical area of coverage. In the next 15–20 years, the main consideration was given to the impact of fires on forest formation process, fire emissions, carbon balance, and fire management’ problems. Also in this paper, the main trends and goals for future research are determined.