The Krasnoyarsk scientist told about the strategies for fighting fires in the taiga in a changing climate. Krasnoyarsk and Canadian scientists conducted a comparative analysis of the fire frequency of taiga forests and offered recommendations for fighting fires in a changing climate. Experts came to a conclusion that in view of an increasing fire hazard, it is necessary to concentrate efforts on extinguishing fires in areas of high natural, social and economic value. The results of the work are published in the Journal Ambio.

Climate warming has led to an increase in the number of fires and burnt areas in Siberia. However, the taiga, in a sense, cannot live without fire. Wildfires support biodiversity in forests, and also contribute to the conservation of certain types of forest adapted to the effects of fire, such as larch forests in the permafrost zone. Moreover, intermittent fires reduce the likelihood of catastrophic ones. This means that the fight against fires should be carried out taking into account the consequences of the effect of fire on the state of forests, as well as taking into account the impossibility to extinguishing all fires.

Scientists from the Krasnoyarsk Science Center of SB RAS, together with their Canadian colleagues, analyzed the character and dynamics of fires in Siberian and Canadian forests over the past twenty-five years, the role of fires in various types of forests, and offered their recommendations for monitoring and fighting fires.

Frequency and geography of forest fires

In recent decades, in Russia there has been an increase in the frequency and area of forest fires in the forests, with more than 70% of fires occurring in Siberia. In some years, the area covered by fire reached 12 million hectares. The border of vegetation fires moves northward, reaching the Arctic coast in Eastern Siberia. The increased fire hazard is considered to be associated with an increase in air temperature, “heat waves” and an increase in the frequency of extreme droughts.

The highest fire rate was recorded in Evenkia, the southern part of Yakutia and Transbaikalia. In mid-latitudes, fires peak in spring and early summer; in August - September, the fire frequency also increases. In the north, the frequency of late and early fires is limited by the lack of heat necessary for the "maturation" of combustible materials, so the highest fire frequency occurs in the middle of summer.

As we move north, the number of fires decreases and the interval between fires increases. While at the latitude of Podkamennaya Tunguska the interval between fires is 50-80 years, in the Arctic, at the northern border of larch forests, it reaches 300 years. At the same time, as we move to high latitudes, the areas of burnt areas increase, as there are more stocks of combustible materials, and fires are hardly extinguished.

Causes and consequences of forest fires

For a fire to occur, a "triad" is needed: combustible materials, their "maturity" for ignition and a source of fire. There are always enough combustible materials in the taiga. Their readiness to ignite is influenced by precipitation, air temperature and humidity, as well as type of vegetation and landscape. The main source of fire in mid-latitudes is the "human factor", which accounts for over 80% of all fires. But farther to the north the population density becomes lower, and thus, is the lower the likelihood of fires. In the north, up to 90% of fires occur due to lightning strikes, which are especially dangerous during "dry thunderstorms". According to recent studies, the frequency of lightning in the Arctic increases by 40% with the one degree warming.

Only every tenth fire can be classified as major, but they account for 90% of all fires. But not all fire-affected forests die, since the consequences depend both on the intensity and type of fire as well as on the type of forest stand. In the crown fire, the destruction of the forest stand is inevitable. Low-intensity fires usually do not cause significant damage to the forest, especially in pine and larch forests, adapted to the fire effects. However, in the case of a sustained ground fire, in which the ground cover and forest litter are burned out, the trees die from the thermal burn of the roots. Such fires are typical in northern larch forests, where the roots are compressed in a narrow surface layer, supported from below by permafrost.

How forests of different types burn

More than half of the Siberian fires occur in larch forests, most of them growing in the conditions of low precipitation and periodic droughts. This is favored by the powerful Siberian anticyclone which is formed every summer. In this zone there may be no precipitation for more than a month. Most of the fires in larch forests are ground ones, because these northern forests are predominantly thinned due to the harsh growing conditions.

Foresters define larch and pine as pyrophytic, “fire-loving” species because fires generally contribute to the conservation of pine and larch forests. Both of these species evolved under conditions of periodic fires, adapting to them and gaining competitive advantages over other tree species. For instance, pine in the absence of fires is displaced by other species (for example, spruce) on poor soils and in wetlands.

“Periodic forest fires are the most important natural factor contributing to the maintenance of a number of forest ecosystems and to the preservation of biodiversity there. For example, the predominance of larch forests in the permafrost zone is due to periodic fires, ” says Doctor of Biological Sciences, head of the forest monitoring laboratory at the V.N. Sukachev Institute of Forest SB RAS, professor of SibFU, Vyacheslav Kharuk.

The role of fires is especially significant for larch growing in permafrost conditions, where larch forests account for up to 80% of all the forests. If to look at the northern larch forests from above, from an airplane or from a satellite, one can see a mosaic of forest stands caused by the impact of fires. The most important consequence of fires is the improvement of conditions for the renewal of larch in burnt-out areas. This is facilitated by the enrichment of the soil with nitrogen, phosphorus and other biogenic elements. In the burned-out areas, drainage and aeration of the soil improves, and the depth of seasonal thawing increases. However, with time, the thawing depth decreases and the tree roots shrink in a gradually narrowing layer. The reason for this is the proliferation of a "pillow" of mosses and lichens, an excellent heat insulator. As the permafrost rises, the inflow of nutrients decreases, and the growth of trees decreases. Along with this, the amount of undergrowth in the stands is sharply reduced. Light larch seeds, hanging on the ground cover, are not able to reach the soil during germination. Moreover, in the soil mineralized by fire, seeds, as a rule, give abundant, rapidly growing undergrowth.

While in larch forests most of the fires are low-intensity ground fires, in dark-coniferous forests formed by fir, cedar and spruce, devastating crown fires prevail. Burns in dark conifers are usually renewed through a change of tree species. In the beginning, mainly aspen and birch appear in such areas, with dark coniferous species settling under their canopy. Fir, cedar and spruce are able to grow in shading conditions, gradually moving into the upper canopy and replacing the “pioneers”. However, a part of the forest area can be occupied for a long time by grasses and shrubs, as well as by aspen and birch.