Long-Term Dynamics of Forest Fires in Southern Siberia

The research focus. Wildfire is a critical environmental disturbance affecting forest dynamics, succession, and the carbon cycle in Siberian forests. Forests of southern Siberia experienced an increase of fire rate. We analyzed spatial and temporal dynamics of burned area in the southern Central Siberian Mountains. We considered burning rate within different forest types: dark needle conifers (DNC) composed by Siberian pine, spruce and fir, light-needle composed by Scotch pine and larch, and mix wood (composed by birch, aspen and conifers). Methods. We used long-term (1982-2021) climatic variables from the ERA5-Land database. Satellite observations included MODIS wildfire data (2002-2021) and gravimetric (GRACE) data (2002-2021) for estimation soil moisture content. We analyzed the spatial distribution of burned areas considering dominant forest stands and terrain (elevation, slope aspect and steepness). Results. We found a significant decreasing trend in burned area. On average, about 978.7 +/- 447.5 thousand ha including 257.1 +/- 154.3 thousand ha of forests are disturbed by fire annually. Light coniferous forests are characterized by the highest degree of the fire disturbance (relative burned area, RBA, was ca. 0.83% per year); whereas DNC stands have the lowest RBA (ca. 0.15% per year). The spatial distribution of fires in light coniferous forests showed predominance of fires on the southern slopes comparing to northern slopes (by 15-20%). We found a decreasing logarithmic trend in burned area between plains and low mountains and high mountains due to lower forest fuel loads and increased amount of precipitation on higher elevations. We also observed lower RBA values (by 300-400%) on steep slopes for light coniferous forests and mixed forests comparing to gentle slopes due to lower available forest fuels. The long-term dynamics of burned area in the region was related to the variation of climatic variables, such as soil moisture (r(2) = 0.70, p < 0.01), moisture content (r(2) = 0.63, p < 0.01) and drought index (r(2) = 0.3, p < 0.05).