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The Productivity of China's Forests: 1961-2005
Reference
Ren, W., Tian, H., Tao, B., Chappelka, A., Sun, G., Lu, C., Liu, M., Chen, G. and Xu, X. 2011. Impacts of topospheric ozone and climate change on net primary productivity and net carbon exchange of China's forest ecosystems. Global Ecology and Biogeography 20: 391-406.

What was done
The authors write that "in recent decades, there has been increased concern that elevated tropospheric ozone (O3) and climate change have [negatively] influenced the ability of China's ecosystems to provide people with essential goods and services." Consequently, in an effort designed to explore this concern, they investigated "the potential effects of elevated O3 along with climate change/variability on NPP [net primary production] and NCE [net carbon exchange] in China's forest ecosystems for the period 1961-2005 using a process-based dynamic land ecosystem model (DLEM, Tian et al., 2005, 2010a,b)," while additionally considering "other environmental factors such as land-cover/land-use change (LCLUC), increasing [atmospheric] CO2 and nitrogen deposition."

What was learned
Ren et al. report that O3 pollution had consistent negative effects on forest production, reducing total NPP by 0.2 to 1.6% from the 1960s to 2000-2005, such that without O3 pollution, carbon uptake rates would have increased by 3.5% in the 1960s and 12.6% in the 6 years 2000-2005. Climate change, on the other hand, had both negative and positive effects on NPP and NCE; and it was thus the major factor controlling the inter-annual variability of these two productivity parameters.

LCLUC also had negative impacts on NPP and NCE; but Ren et al. found that "nitrogen deposition alone could compensate for the combined negative effects of O3 and LCLUC in China." They also report that an increase in NPP occurred in the CO2-N combination simulation, which they say "was consistent with previous studies (e.g., Ollinger et al., 2002; Felzer et al., 2004; Hanson et al., 2005)." And they found that CO2 and nitrogen deposition working together "could offset the combined negative effects of O3 pollution, climate change and LCLUC on annual NCE."

What it means
The two phenomena of atmospheric CO2 enrichment and nitrogen deposition -- both of which are by-products of the Industrial Revolution -- provide powerful antidotes for the negative effects of ozone pollution, land-cover/land-use change and various deleterious climatic phenomena with regard to their impacts on NPP and NCE in China and, by inference, other parts of the world as well.

References
Felzer, B.S., Kicklighter, D.W., Melillo, J.M., Wang, C., Zhuang, Q. and Prinn, R. 2004. Effects of ozone on net primary production and carbon sequestration in the conterminous United States using a biogeochemistry model. Tellus 56B: 230-248.

Hanson, P.J., Wullschleger, S.D., Norby, R.J., Tschaplinski, T.J. and Gunderson, C.A. 2005. Importance of changing CO2, temperature, precipitation, and ozone on carbon and water cycles of an upland-oak forest: incorporating experimental results into model simulations. Global Change Biology 11: 1402-1423.

Ollinger, S.V., Aber, S.D., Reich, P.B. and Freuder, R.J. 2002. Interactive effects of nitrogen deposition, tropospheric ozone, elevated CO2 and land use history on the carbon dynamics of northern hardwood forests. Global Change Biology 8: 545-562.

Tian, H.Q., Liu, M.L., Zhang, C., Ren, W., Chen, G.S., Xu, X.F. and Lu, C.Q. 2005. DLEM -- the Dynamic Land Ecosystem Model, user manual. Ecosystem Science and Regional Analysis Laboratory, Auburn University, Auburn, Alabama, USA.

Tian, H., Chen, G.S., Liu, M.L., Zhang, C., Sun, G., Lu, C.Q., Xu, X.F., Ren, W., Pan, S.F. and Chappelka, A. 2010a. Model estimates of net primary productivity, evapotranspiration, and water use efficiency in the terrestrial ecosystems of the southern United States during 1895-2007. Forest Ecology and Management 259: 1311-1327.

Tian, H., Xu, S., Liu, M., Ren, W., Zhang, C., Chen, G. and Lu, C.Q. 2010b. Spatial and temporal patterns of CH4 and N2O fluxes in terrestrial ecosystems of North America during 1979-2008: application of a global biogeochemistry model. Biogeochemistry 7: 1-22.

Reviewed 29 June 2011