Monitoring of Post-fire Effects and Vegetation Recovery in Larch Forests of Central Siberia Using Remote Sensing Observations

In boreal zone of Siberia up to 3-10 million hectares of larch dominated forests are exposed to fires every year with an increasing trend in burned area observed during the last two decades. According to forecasts of climate changes warmer and drier climate will result in higher fire frequency and larger burned area. Fire-caused changes in the vegetation cover can provoke the soil thermal regime changing that in turn can affect the seasonally thawed layer state and its dynamics in future. So among other factors permafrost is influenced by wildfires that are one of the main disturbance factors in the boreal zone of Siberia. The seasonally thawed layer anomalies in the northern high latitudes are of high interest to the scientific community since its large spatial extent and climatic changes in the region. Changes in permafrost dynamics could contribute to tree line migration and alterations in the mosaic structure of boreal forests.

We analyzed the vegetation dynamics and long-term thermal anomalies for fire-disturbed sites in the permafrost zone of Siberia using the remote sensing data from Terra/Aqua MODIS satellite systems. Time series of NDVI and NBR indices as well as land surface temperature were created at pixel level for the period of 2000 - 2018. We considered post-fire dynamics separately for areas of high, moderate and low burn severity using dNBR to discriminate between them.

The land surface temperature on fire-disturbed sites was 15-35% (3.9-4.6°C) higher comparing to undisturbed background areas during next post-fire summer season. One year after fire on disturbed sites NDVI was ~80% and NBR was about 30% of background values. The recovery period for NDVI is generally 7-10 years while for NBR it takes about 15 - 20 years to return to pre-fire state. Surface temperature anomalies also remain significant for more than 15 years after the fire event according to satellite data and ground-based measurements. The recovery rate for thermal anomalies was 2.5 times lower than for NDVI. It makes it possible to consider this factor of long-term influence on the seasonal thawed soil layer as one of the most significant.

Acknowledgments: This research was supported by the Russian Foundation for Basic Research (RFBR), projects 18-05-00432, 17-04-00589 and 18-41-242003.