Spatial and Temporal Patterns of Carbon Exchanges between the Atmosphere and Terrestrial Ecosystems of China Hanqin Tian Ecosystem and Regional Studies Group Auburn University, AL 36849, USA & NASA IDS Project Participants*

*The NASA IDS Project Participants: Jerry M. Melillo, David Kicklighter, Ben Felzer, The Ecosystem Center, Marine Biological Laboratory, Woods Hole, USA. Steven Running, Maosheng Zhao, Qiaozhen Mu, University of Montana, Missoula, USA. Jiyuan Liu, Guoyui Yu, Aifeng Lv, Chaoqun Lv, Wei Ren, Xiaofeng Xu, IGSNRR, Chinese Academy of Sciences, Beijing, , China. Ranga Myneni, Yuri Knyazikhin, Nikolay Shabanov, Boston University, Boston, USA. Mingliang Liu, Shufen Pan, Hua Chen, Siqing Chen, Guangsheng Chen, Chi Zhang, Auburn University.

–The US carbon sink: Forest inventory, bookkeeping model--land use change, and inverse model (Birdsey and Health, 1995, Houghton et al. 1999, Capersen et al. 2000, Pacala et al. 2001) ( Pg/yr). –The Eurasian carbon sink has received less attention. IPCC TAR (Prentice et al. 2001): both North America and Eurasia served as carbon sinks during the 1990s, suggesting a net sink of Pg C yr-1 that is distributed relatively evenly between North America and Eurasia. From both scientific and policy perspectives, it is of critical importance to quantify regional carbon budget and mechanisms controlling the carbon cycle.

We haven’t succeeded in answering all problems. The answers we have found only serve to raise a whole set of new questions. In some ways, we feel we are as confused as ever, but we believe we are confused on a higher level and about more important things.

Everything about China, good or bad, is BIG! China is the world’s third largest country, the most rapidly developing nation and home to 1.3 billion people. Since the early 1980s, the unprecedented combination of economic and population growth has led to a dramatic land transformation across the nation. China is “Natural Laboratory” for studying dynamics of coupled natural and human systems as well as the carbon cycle.

Total Population: 1,306,313,812 (July 2005 est.)

Population distribution of 2000 in China (cell size = 1 km, Unit: persons per km2) 0 – > 2200

Chinese Population urbanized (%) Rapid urbanization in China

Liu, J., H.Q. Tian, M. Liu, D. Zhuang, J.M. Melillo and Z. Zhang (2005). Geophys. Res. Lett., 32, L02405, doi: /2004GL Large-scale land transformation estimated with satellite data

OBJECTIVES: Our study will be organized by two linked questions: Q1 - HOW HAVE PRIMARY PRODUCTION AND CARBON STORAGE CHANGED IN CHINA OVER THE PAST TWO DECADES? Q2 - WHAT MECHANISMS HAVE HAD MAJOR EFFECTS ON CHANGES IN THESE FLUXES AND STOCKS? We will consider the relative roles of: (a) climate variability, (b) changes in land cover and use, (c) changes in fire disturbance, (d) changes in the chemistry of precipitation (particularly nitrogen), and (e) changes in the composition of the atmosphere (carbon dioxide, ozone).

APPROACHES: Here we try to combine remote-sensing data (MODIS, AVHRR, Landsat-TM/ETM) and a set of biogeochemical simulation models (TEM, Biome-BGC and A new model) to quantify the consequences of land transformations and other environmental changes on productivity in forests and other “natural” ecosystems and carbon sequestration.

Satellite Data Eddy Flux Ecosystem Experiments Flask Data MeasuringModeling Synthesis The Integrated Approach Quantifying Regional C Dynamics

BIOME-BGC

The Terrestrial Ecosystem Model (TEM)

A New Model of Coupled Biogeochemical Cycles

Data Development Climate Land use history O 3 CO 2 Other data: elevation, soil texture, potential vegetation

Historical Cropland & Urban area distribution (10 X 10 km)

Annual mean temperature (0.1 ℃ ) Average annual precipitation (0.1mm)

Mean annual N deposition in 1990s in China (mg N/m2)

Mean surface O 3 concentration in 1990s in China (Unit: D40)

Simulation Experiments 1.Climate Only 2.CO 2 only 3.Land use only 4.O 3 only 5.Climate + Land use 6.Climate + CO 2 + Land Use 7.Climate + CO 2 + O 3 8.Climate + CO 2 + O 3 + Land use

TEM-based estimate on vegetation and soil carbon in 2000 (Climate_CO2_LUCC_O3) Vegetation Carbon Soil Organic Carbon gC/m 2

Change in total carbon storage (gC/m 2 )

Mean annual Net Carbon Exchange ( ) (gC/m 2 /yr) Mean annual Net Carbon Exchange ( ) (gC/m 2 /yr)

Ozone effect on carbon storage during (gC/m 2 )

Annual Net Carbon Exchange (PgC/yr)

Cumulative Net Carbon Exchange (Pg C)

Relative contribution of CO 2, climate, land use and O 3 to carbon fluxes during (Pg C/yr)

Annual NPP, HR, NEP and NEE trends during derived from Biome-BGC. NPP RHRH NEP NEE

Decadal variations in carbon emission induced by forest fires across China

a) Mean AVHRR NPP from b) NPP trend from c) Mean MODIS NPP d) Mean NPP as estimated by a new model. a.b.c. d.

CH 4 emission from cropland derived from a new coupled biogeochemical model

Summary The combined effect of climate, CO 2, land use and O 3 on net carbon exchange show that terrestrial China acted as a small carbon sink ( 64 Tg C per year) during , but showing substantial year-to-year variation. For the time period from 1980 to 2000, both land use and CO 2 resulted in carbon uptake while climate and O 3 led to carbon release. During , however, land- use change resulted in a large release of carbon to the atmosphere (about 12 Pg C). CH 4 emission from agricultural land varied from 6 to 16 Tg C per year. Fire- induced carbon emission is about 11.3 Tg C per year. In any year over the period , net carbon exchange can be very large in one location but very small or negative in another location because of the spatial heterogeneity of vegetation, soils and climate. Additional factors needed to be considered include N deposition, Forest management and agronomic practices. In the future, Model intercomparison needs to be done. Also modeled results need to be evaluated against field data.

ACKNOWLEDGMENT This study is supported by NASA Interdisciplinary Science Program (NNG04GM39C).