Land surface temperature dynamics during post-fire succession in boreal forests

Background/Question/Methods

Wildfire is the most important disturbance agent in boreal forests. Fire and post-fire succession are linked to diverse changes in ecosystem function and structure shaping land-atmosphere interactions for decades after the disturbance event. However, how wildfire disturbance alters differences between land surface and air temperatures in boreal forests still remains uncertain hampering our understanding of near-surface climate impacts of wildfires. Here, we analyse surface energy balance observations from 17 eddy covariance flux tower sites across fire disturbance chronosequences in the North American boreal biome to identify the main drivers of post-fire changes in land surface-air temperature gradients. We use 102 years of observations to quantify winter and summer changes in important ecosystem properties such as evaporative fraction, aerodynamic conductance, and albedo following stand-replacing fire disturbances.

Results/Conclusions

In the summer, we find that the surface-air temperature gradient increases after the fire disturbance while, in the winter, the temperature gradient decreases. Decreased aerodynamic conductance contributes mainly to the post-fire surface heating in the summer while increasing albedo mainly explains winter cooling. Evaporative fraction increases initially in the first few decades after the post-fire disturbance. However, during drought years, the evaporative fraction declines rapidly during the same period. Our results provide important insights into fire impacts on ground thermal regimes in boreal forests and highlight the reduced capacity of post-fire forests to reduce land surface temperatures during heatwave events while cooling the land surface during the winter.