Natural Fires in the Larch Forest of the Cryolithozone: Monitoring and Firefighting Strategy under the Conditions of a Changing Climate

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.