[M-IS01] Environmental, Socio-Economic and Climatic Changes in Northern Eurasia

[MIS01-P08] Permafrost drives climatology, energy and mass exchange in permafrost Larix gmelinii compared to permafrost-free Pinus sylvestris in central Siberia

★Invited Papers

*Nadezhda Tchebakova¹、Viacheslav I. Zyryanov¹、Olga A. Zyryanova¹、Elena I. Parfenova¹、Takuya Kajimoto²、Yojiro Matsuura³ (1.Institute of Forests, Siberian Branch, Russian Academy of Sciences、2.Niigata University, Sado Island Center for Ecological Sustainability, Niigata, Japan、3.Forestry and Forest Products Research Institute, Global Strategy Division, Tsukuba, Japan)

キーワード：permafrost , energy and carbon flux, heat and water balance, water use efficiency, Scots pine, Gmelin larch

Inter-annual and seasonal variations of energy, vapor water, and carbon fluxes and associated climate variables in a middle taiga pine (Pinus sylvestris) forest on sandy soils and in a northern taiga larch (Larix gmelinii) forest on permafrost in central Siberia were studied from eddy covariance measurements acquired during the growing seasons of 1998-2000 and 2004-2008, respectively. Both the pure Scots pine of 215-yr-old and pure Gmelin larch of 105-yr-old forests naturally regenerated after forest fires, differed by their tree stand characteristics, and grew in extremely contrasting environments with distinctive climatic and soil conditions (Fig. 1. Study sites: the Larix gmelinii with Pleurozium schreberi and Aulacomnium turgidum and dwarf-shrubs forest floor (left) and the Pinus sylvestris with Cladonia, Cladina, and Cetraria forest floor (right)). Net radiation was greater in the pine forest due to higher values in summer months and a longer growing season. Sensible heat flux was the larger term in the radiation balance in both forests. Bowen ratio stayed between 1 and 2 during the growing season and was as high as 8-10 in dry spring in both forests. In the dry summers, latent heat explained 70-80% of the daily net ecosystem CO₂ exchange (NEE) variation in both forests. The average NEE was significantly smaller in the larch ecosystem -4 µmol m^-2s^-1 compared to -7 µmol m^-2s^{-1 in the pine forest. NEP for the growing season was 83 in the larch forest on continuous permafrost and 228 g C m-2 in the pine forest on warm sandy soils. Water use efficiency was 5.8 mg CO}₂ g^-1H₂O in the larch forest and 11 mg CO₂ g^-1H₂O in the pine forest and appeared to be consistent with that in boreal forests. As a result of the forest structure change from Gmelin larch to Scots pine due to the permafrost retreat in a warming climate, the potential feedbacks to the climate system may be both negative and positive. Negative: while the permafrost retreats methane emissions to the atmosphere may exceed C-sink in the larch forest reversing C-sink into C-source. Positive: in the permafrost-free pine forests which would replace permafrost larch forests, C-sink would be increasing and uptaking CO₂ from the atmosphere. Thus, positive potential feedbacks to the climate system may take place that slow down climate warming.