ISSN 0012-4966, Doklady Biological Sciences, 2013, Vol. 450, pp. 173–176. © Pleiades Publishing, Ltd., 2013. Original Russian Text © A.V. Olchev, O.A. Deshcherevskaya, Yu.A. Kurbatova, A.G. Molchanov, E.Yu. Novenko, V.B. Pridacha, T.A. Sazonova, 2013, published in Doklady Akademii Nauk, 2013, Vol. 450, No. 6, pp. 726–730. 173 The structure, species composition, and productiv- ity of forest ecosystems are determined by a number of factors, with climatic conditions as the major one. Incoming solar radiation, air temperature and humid- ity, and soil moisture conditions regulate plant photo- synthesis, respiration and transpiration, determining the growth and developmental patterns of plant com- munities. The modern climate changes appeared mainly in increase of the air temperature, alterations in the gas composition of the air and land surface moistenning conditions may evidently influence the dynamics and rate of biophysical and biochemical processes in plants and soil and, as a consequence, lead to changes in the intensity of CO 2 and H 2 O exchange between plants and ambient air. In a long- term perspective, this may influence sustainable development of forests and lead to changes in their species composition and spatial distribution of vari- ous species [1]. Possessing by a high sensitivity to changes in envi- ronmental conditions, forests also have a significant feedback effect on the climate system. Actively absorb CO 2 from the atmosphere during photosynthesis, accumulating carbon in the aboveground and under- ground biomass, and retaining it in a fixed state during a considerable time period, they enhance the mainte- nance of natural CO 2 balance in the atmosphere, mit- igating the possible negative ecological consequences of the increasing greenhouse effect. Directly influenc- ing the radiation, heat, and water regimes of the ground surface and atmospheric surface layer, forests protect the ground surface from overheating in sum- mer as well as regulate evaporation processes. Preserv- ing moisture incoming to the ground surface with pre- cipitations, they enhance the formation of a stable river discharge. The study of climate and forest vegetation interac- tions requires integrated experimental and modelling studies, first and foremost, aimed at analysis of the natural variation and sensitivity of different forest types to environmental changes, stability of the forest systems, and assessment of the effects of the changes in the structure and species composition of forest plant communities on climate. In this study, the sensitivity of the CO 2 and H 2 O exchange components in forest ecosystems to pro- jected climate changes by the end of the 21st century has been estimated in a case study of southern taiga spruce forests of European Russia using results of modelling experiments. A model-based approach allows not only to estimate the spatial and temporal variability of the exchange processes, but also to pre- dict the response of various plant communities to changes in climatic conditions, which cannot be pro- vided using only experimental data. In particular, the data obtained in the study on the changes in net exchange of CO 2 (NEE) and evapotranspiration (E) under changing climatic conditions make it possible, on the one hand, to assess the possible response of the forest ecosystems to external impacts and, on the other hand, to determine the potential contribution of southern taiga forests to the change in the atmospheric balance of greenhouse gases by the end of the 21st cen- tury. To predict the possible alterations in the forest CO 2 and H 2 O exchange components upon climate changes, a process-based MixFor-SVAT model has been used [8, 10, 11]. The main concept of this model is an inte- grated description of physical and biological processes CO 2 and H 2 O Exchange in the Forest Ecosystems of Southern Taiga under Climate Changes A. V. Olchev a , O. A. Deshcherevskaya a , Yu. A. Kurbatova a , A. G. Molchanov b , E. Yu. Novenko c , V. B. Pridacha d , and T. A. Sazonova d Presented by Academician Yu.Yu. Dgebuadze September 28, 2012 Received September 28, 2012 DOI: 10.1134/S0012496613030216 a Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow, Russia b Institute of Forest Science, Russian Academy of Sciences, Uspenskoe, Moscow oblast, Russia c Institute of Geography, Russian Academy of Sciences, Moscow, Russia d Institute of Forest, Karelian Scientific Center, Russian Academy of Sciences, Petrozavodsk, Russia GENERAL BIOLOGY