Long-termecologicalconsequencesofforestfiresinthecontinuous permafrostzoneofSiberia

Abstract

Wildfiresareanimportantfactorincontrollingforestecosystemdynamicsacrossthecircumpolar borealzone.Animprovedunderstandingoftheirdirectandindirect,short-tolong-termimpactson vegetationcoverandpermafrost–vegetationcouplingisparticularlyimportanttopredictchangesin carbon,nutrientandwatercyclesunderprojectedclimatewarming.Here,weapplydendrochronologicaltechniquesonamulti-parameterdatasettoreconstructtheeffectofwildfiresontreegrowth andseasonalpermafrostthawdepthinCentralSiberia.Basedonannually-resolvedandabsolutely datedinformationfrom19Gmelinlarch(Larixgmelinii(Rupr.)Rupr.)treesandactivesoillayer thicknessmeasurements,wefindsubstantialstand-leveldie-off,aswellastheremovalofground vegetationandtheorganiclayerfollowingamajorwildfirein1896.Reducedstemgrowthcoincides withincreasedδ13Cinthecelluloseofthesurvivingtreesduringthefirstdecadeafterthewildfire, whenstomatalconductancewasreduced.Thenextsixtosevendecadesarecharacterizedbyincreased permafrostactivesoillayerthickness.Duringthisperiodofpost-wildfireecosystemrecovery, enhancedtreegrowthtogetherwithpositiveδ13Candnegativeδ18Otrendsareindicativeofhigher ratesofphotosynthesisandimprovedwatersupply.Afterwards,athinneractivesoillayerleadsto reducedgrowthbecausetreephysiologicalprocessesbecomelimitedbysummertemperatureand wateravailability.Revealinglong-termeffectsofforestfiresonactivesoillayerthickness,ground vegetationcompositionandtreegrowth,thisstudydemonstratestheimportanceofcomplex vegetation–permafrostinteractionsthatmodifythetrajectoryofpost-fireforestrecoveryacrossmuch ofthecircumpolarborealzone.Tofurtherquantifytheinfluenceofborealwildfiresonlarge-scale carboncycledynamics,futureworkshouldconsiderawiderangeoftreespeciesfromdifferent habitatsinthehigh-northernlatitudes.