DYNAMICS OF A TAIGA-PERMAFROST COUPLED SYSTEM IN EAST SIBERIA
UNDER THE GLOBAL WARMING
Tetsuzo YASUNARI (1)(4) , Ningning ZHANG(2), and Takeshi OHTA(3)(4)
(1) Hydrospheric Atmospheric Research Center(HyARC), Nagoya University, Japan
(2) Institute of Atmospheric Physics(IAP), Chinese Academy of Scienc, China
(3) Graduate School of Bio-agricutural Studies(GSBS), Nagoya University, Japan
(4) Study Consortium for Earth-Life Interactive System (SELIS), Nagoya University
E-mail: [email protected]
Taiga in the boreal zone plays important and sensitive roles in global and regional water–energy–carbon
(WEC) cycles and in the climate system. Recent in situ observations (e.g., Ohta et al., 2001[1], 2006[2];
Sugimoto et al., 2002[3]) suggested that the Larch-dominated taiga is strongly coupled with the permafrost
underneath the taiga forest through the seasonal and interannual variations of WEC processes. In other
words, the taiga (represented by larch trees) and the permafrost may behave as a coupled eco-climate
system across a broad boreal zone of Siberia as shown in Fig.1. However, neither field-based
observations nor modelling experiments have clarified the synthesized dynamics of this system. Here,
using a new dynamic vegetation model (DVM) coupled with a permafrost model, we reveal the
interactive processes between taiga and permafrost in east Siberia. The model demonstrates that under the
present climate condition , larch trees help control the seasonal melting of permafrost, which in turn
provides sufficient water to the larch trees. Without permafrost processes, larch may not survive and may
be replaced by a dominance of pine and other species that can tolerate drier hydro-climatic conditions.
Forest fires also play a role in preserving the taiga larch forest. Climate warming sensitivity experiments
involving increased air temperature has also shown that this coupled system would no more be
maintained under the warming of about 2°C or more as shown in Fig. 2. Under this condition, larch forest
will be replaced by sub-boreal forests (e.g., dark conifer and other deciduous species) , and the forest
would be decoupled with the permafrost processes, with decreasing of the total biomass. This study thus
suggests that future global warming could drastically alter the taiga–permafrost coupled system, with
associated changes of WEC processes and feedback to climate. These results will appear as a coming
paper of Zhang et al. (2011)[4].
References:
[1] Ohta, T., T. Hiyama, H. Tanaka, T. Kuwada, T. C. Maximov, T. Ohata, and Y. Fukushima (2001),
Seasonal variation in the energy and water exchanges above and below a larch forest in eastern Siberia,
Hydrol Process, 15(8), 1459-1476.
[2] Ohta, T., et al. (2008), Interannual variation of water balance and summer evapotranspiration in an
eastern Siberian larch forest over a 7-year period (1998-2006), Agr Forest Meteorol, 148(12), 1941-1953.
[3] Sugimoto, A., N. Yanagisawa, D. Naito, N. Fujita, and T. C. Maximov (2002), Importance of
permafrost as a source of water for plants in east Siberian taiga, Ecological Research, 17(4), 493-503.
[4] Zhang, N.-N., T. Yasunari and T. Ohta (2011), Dynamics of Larch Taiga-Permafrost Coupled system
in Siberia under climate change, Environmental Research Letters, in press.
Figure 1:
Schematic diagram of feedbacks of soil, vegetation and fire in the Siberian taiga–permafrost
system considered in this study (right-side diagram); spatial distribution of larch taiga (left-bottom figure, red
area) and boundary of permafrost (left-bottom figure, dashed line & blue line); location (left-bottom figure,
green star) and climate of Yakutsk (left-top figure). In the schematic diagram: arrows show force directions
between each factor. ‘+’ (‘-‘) means the following the forces direction, there is a positive (negative)
correlation between two factors, and ‘±’ means the correlation is still not clear. The thicker arrows indicate the
processes which were better considered in the model simulation. Dashed arrow indicates the process which is
not considered in this study. The words beside each arrow indicate the variables that control such process.
Figure 2: Above-ground total biomass (with fractional components of major species) for CNTLrun (left bar)
and NP run (right bar) simulated under five different climate conditions. Five bar groups represent those (from
left to right) for the present climate condition; for temperature conditions of +1.℃(above the present); +2℃;
+4℃, and + 4℃ plus precipitation +20% (above the present). The name of each experiment was shown on
the top of the bar. Two Dashed lines in the upper part show changes of summer (JJA) mean soil water for
CNTL run (square marks) and NP run (diamond marks), respectively. Note the changes of major species
contributing to the total biomass under the different climate conditions.