Wildfire Dynamics in Pine Forests of Central Siberia in a Changing Climate

Climate change increases the frequency of forest fires throughout the entire boreal zone. This paper examines the long-term wildfire dynamics in pine forests of Central Siberia, relationships between environmental and climatic variables on the one hand and the occurrence frequency of fires and size of burnt forest areas on the other, and the postfire dynamics of vegetation cover productivity. A coupled analysis of ground survey data, remote sensing data (spectroradiometric and gravimetric information collected by the Terra/MODIS and GRACE satellites), and dendroecological data is performed. In the period from the 18th to the 20th century, fire return intervals decreased from 33 to 20-25 years. No statistically significant trends in fire occurrence frequency were identified in the current century; however, catastrophic (i.e., affecting more than 1 million ha) fires were observed in its second decade, and both the number of fires and size of burnt areas have significantly increased (by 3.5 and 3.0 times, respectively). The frequency of fires and size of burnt areas closely correlate with wetting and temperature conditions in the prefire period. Furthermore, fire statistics parameters correlate with wetting conditions (precipitation amount, moisture content in the ground cover and soil, and the Self-Calibrated Palmer Drought Severity Index (sc-PDSI)) stronger than with air temperature. It is shown that equivalent water thickness values obtained using gravimetric methods can be used in fire risk assessments. High correlation levels were identified between the growth index of pine trees and vegetation cover productivity indices (i.e., gross primary productivity (GPP) and net primary productivity (NPP)) generated based on remote sensing data. The results indicate that these indices can be used to estimate forest stand productivity dynamics. The vegetation cover productivity and the radial growth index of pine trees in burnt areas quickly (within a decade) restore to prefire values, which indicates that northern pine forests retain their carbon sequestration function despite climate change and the increasing frequency of fires.