The environmental legacies of tundra fires in the Noatak River Valley of Alaska
Ben Gaglioti, Water and Environmental Research Center, University of Alaska Fairbanks
Observing how permafrost and vegetation respond to tundra fires in particularly flammable regions can provide useful lessons on how fires will impact areas where burn rates are expected to rise in a warming climate. I will present results from a project funded by the Joint Fire Science Program where we use shrub dendrochronology, active-layer depth measurements, and remotely-sensed vegetation indices inside and outside historical fires in the relatively pyrogenic watershed of the Noatak River. Our results indicate that tundra vegetation is highly resilient to fires, as vegetation indices recover to pre-fire values within three years of burning. Fires often led to enhanced primary productivity for at least several decades following burns. Several lines of evidence indicate that this post-fire ‘greening’ process is related to fire-induced permafrost thaw and shrub expansion. In addition to this greening effect, we found that the vegetation in burned areas can become less sensitive to summer temperatures following fires. I hypothesize that this post-fire loss of climate sensitivity occurs because fires can thaw permafrost and release nutrients which spurs plant growth and enables Arctic plants to be less limited by summer temperature variability. In this way, tundra fires can both rapidly facilitate vegetation change in the Arctic and make post-fire vegetation communities less responsive to subsequent warming trends. Given the short length of the historical record, we still do not know how long these post-fire environmental legacies persist in the Noatak. I will close the talk by discussing the implications these results have on vegetation trends in a warmer, more flammable Arctic.