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Carbon Budgets in Forest and Grassland Ecosystems

Terrestrial carbon (C) emissions are a major cause of human-induced climate change. Capturing CO2 from the atmosphere in soil and vegetation could be a major part of the solution. China is a key region for global and regional C studies. Changing climate and numerous social and economic pressures have strongly affected terrestrial C budgets in China.

Forests and grasslands contribute 46.3% and 25.6%, respectively, to global terrestrial C stocks. Boreal and temperate forests have contributed almost all of the global C sink of the forest sector during the past 20 years (1990–2007). The C captured by tropical forests has been roughly balanced by land-use changes in the tropics. Temperate grasslands in China are the third largest grassland area in the world, accounting for 40% of the country’s land area. Given that most of these lands are located in arid and semi-arid areas, they are very sensitive to climate change. Young- and middle-aged forests account for 68% of the forested area in China. However, research on soil C storage and the sequestration potential of these forests and grasslands is very limited. It is critical to understand the C sequestration potential and the responses of forests to climate change in China.

Given the importance of natural forests and grasslands in the regional and global C cycles and the uncertainties related to carbon budgets in these ecosystems, IAE has identified carbon budgets of natural forests and grasslands as one of its primary research directions. This program aims to develop methods that can quantify the carbon sequestration potential in natural forest and grassland ecosystems; examine the effects of ecological stoichiometry on carbon balance in natural ecosystems; explore the drivers and controls underlying C sequestration potential; and construct ecological models to predict carbon balance in terrestrial ecosystems at different hierarchical levels under global climate change. This work will generate important information for predicting the effects of global climate change on the C cycle in natural ecosystems and for international negotiations regarding greenhouse emissions.

Currently there are eight groups in IAE focusing on carbon processes in forests and grasslands ¾ Ecological Stoichiometry Group, Biogeochemistry Group, Seed Ecology Group, Forest Ecological Engineering Group, Digital Forestry Group, Eco-Climate Group, Plantation Ecology Group, and the Eco-Boundary Group. There are 30 research scientists, 20 Ph.D. students, and 30 master’s students within these eight groups. Among these scientists, there are two lead principal investigators of the “973 Project” and two Hundred-Talent Program scientists of the Chinese Academy of Sciences. The majority of them have undertaken extensive collaboration with international scientists. Some ongoing projects of these groups are supported by NFC and MOST, and are focusing on key issues related to C cycles

This innovative research will take advantage of the Institute’s research facilities. We have four long-term field research stations, two of which are national key field stations, and two large-scale grassland transects and forest chronosequences along environmental gradients. We use OTC (open top chamber) to study the response of trees to long-term CO2 enrichment. We also have facilities for long-term in-situ nitrogen addition and precipitation manipulation, which are deployed to study the response of carbon-nitrogen-water cycles in grassland and forest ecosystems to global environmental changes. We have established a carbon flux measurement system above the forest canopy, which utilizes the first forest canopy crane employed in China.

In the last five years, we have made great progress in diverse topics related to carbon budgets in natural forests and grasslands: 1) The effects of climate warming on biogenic volatile organic compounds (BVOC) emissions as affected by precipitation patterns; 2) Decreases in soil C storage triggered by climate warming and increases in C sequestration induced by increased precipitation in semiarid grassland ecosystems; 3) Alterations in C partitioning within above- and below-ground pools due to N addition, and their significant effects on total ecosystem C pools in semiarid grasslands; 4) Two novel methods for refining long-term CO2 flux measurements; 5) The role of old-growth natural forests in the Changbai Mountain region as a carbon sink; 6) Non-additive effects in decomposition processes of mixed fir and broad-leaved forest litter; and 7) Local effects of nutrient release on the process of litter decomposition.

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