Ninth International Conference on Permafrost ... - IARC Research

Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s torganic cover—most intensively enrich mineral horizonswith organic matter. A similar trend was observed for thesuccession developing through the stage of dense forest.Thus, the influence of fires on soil carbon pools has a dualnature: in the first stages, “expected” dramatic reductionof carbon pools in organic horizons and less expressed inmineral horizons; in the later stages, postpyrogenic effectof organic matter accumulation on the mineral surface andOC enrichment of mineral horizons due to intense recoveryprocesses in the ecosystem.ReferencesTarabukina, V.G. & Savvinov, D.D. 1990. Influence of fireson cryogenic soils. Novosibirsk: 120 pp.Figure 3. Alteration of OC densities in organic and mineral horizonsin dependence to fire age and/or type of postpyrogenic succession(for the legend see Fig. 2).I – consecutive postpyrogenic development of larch open forestII – development through stage of dense larch forestdepressions (1–4 m in diameter) indicate an intersection ofice wedges, which partially melt when vegetation is destroyedduring the fire. The soil profiles are strongly disturbed bycryoturbations.Postpyrogenic successions of vegetation and soils arecyclical. This fact provided an opportunity to estimatedynamics of soil features including organic carbon (OC)densities (in similar lithological and geomorphologicalconditions) (Fig. 3).OC densities in mineral horizons were calculated for the50 cm layer. OC storage in organic horizons was estimatedfor its actual thickness. “Expected” postpyrogenic reductionof OC density is most significant in organic horizons (from3.9 to 0.5 kg C/m 2 ). However, 60 years after the fire, OCdensity reached its initial values in larch open forest and evenexceeded initial values in a highly productive ecosystem ofdense larch forest (∆ = 1.7 kg C/m 2 ) with thick moss coverstimulating active peat accumulation. Alteration of OCdensities in mineral horizons is less evident. For the larchopen forest ecosystem 30 years after the fire, the reductionwas fixed (∆ = -1.6 kg C/m 2 ); however, at the next measuringpoint (60 years after the fire), an intensive increase has beenrevealed (∆ = 2.5 kg C/m 2 ). Such “unobvious” change wasprimarily induced by two factors: active layer thicknessand cryoturbations. According to our data, in a 30- to 60-year period after the fire, active layer thickness decreases,reaching its initial values; at this time cryoturbations reachthe highest intensity. Cryoturbations in the presence of twoconditions—close permafrost table and already formed thick212