Background

Global Change and Terrestrial Ecosystems (GCTE) is a project of the International Geosphere-Biosphere Program (IGBP) with the scientific objectives of: (1) predicting the effects of changes in climate, atmospheric composition, and land use on terrestrial ecosystems, including agroecosystems and biodiversity; and (2) determining how these effects lead to feedbacks to the atmosphere and the physical climate system.

During the 1999-2000 financial year GCTE has been engaged in activities on (1) the carbon cycle, (2) food and fiber production, (3) biodiversity and landscape complexity, and (4) other IGBP-wide activities.

The Science of the Carbon Cycle

Improving our understanding of the carbon cycle at various spatial and temporal scales requires the integration of multiple and complementary methods. GCTE along with the rest of IGBP, IHDP and WCRP is developing an international Science and Implementation Plan to coordinate and foster new research on the carbon cycle. GCTE is contributing to the new integrated initiative by providing process-level information on flux control mechanisms and vegetation dynamics under climate change.

For instance, the Network of elevated CO₂ experiments studies key ecosystem processes under novel environmental conditions of high atmospheric CO₂, nitrogen deposition, and altered water availability. Much in the same way, the Network of Experimental Warming Studies has shown in a recent meta-analyses the positive short-term of warming on increased nitrogen availability and plant productivity, but negative impacts on soil moisture and soil release of CO₂ to the atmosphere (View the results).

Information like this one plays a critical role to further develop and validate stand, regional and global models to make predictions of the effects of global change on terrestrial ecosystems. Globally, Dynamic Global Vegetation Models (DGVMs) are the only type of global models that explicitly represent the interactions of ecosystem carbon, water, and energy exchange with vegetation dynamics (distribution and physionomy of vegetation structure). A recent intercomparsion of six DGVMs showed that the average global net ecosystem productivity (net carbon balance) will saturate within the next 30-50 and the carbon sink strength of terrestrial ecosystems will decline thereafter (view results).

Predicted biome and species distribution shifts due to climate and land-use change will also bring changes in soil carbon deposition and decomposition due to changes in rotting patterns and densities. In a recent synthesis, the analyses of 2,700 soil profiles on vertical distribution of soil organic carbon down to three meter were summarized (view results). For instances, in shrublands, the amount of soil carbon in the second and third meter is 77% of that in the fist meter which show the importance to account for deep pools of carbon.

The carbon cycle will be also affected by those actions taken in compliance to the Kyoto Protocol. GCTE using some of the Soil Organic Mater network (SOMnet) has calculated the potential carbon sequestration due to soil management. For instances, application of no-till arable lands, and incorporation of animal manure and straw in soils are effective mechanisms to increase soil carbon storage. The panel shows the maximum percentage offset of European 1990 CO₂-carbon emissions.

Food and Fiber Production

Agroecosystems are essential to human well-being. Many, however, are already threatened by damage to soil and waste resources, and climate and atmospheric changes will further affect these stressed and rapidly changing systems. The ability to capitalize on the potential benefits of global change while avoiding or reducing the adverse effects require a strong predictive capability. That was the topic of the Conference entitled: "Food and Forestry: Global Change and Global Challenges". View the contents of the special issue stemming from the Conference to be published in Agriculture, Ecosystems and Environment.

Global change will not only change crop physiology and the associated production but will also affect the plant-pest complex that can be responsible for large losses of crop production. Potato late blight is an excellent model system for studying a crop-disease complex within the context of global change, as the disease is both economically important and highly sensitive to weather patterns (view results). GCTE has recently established a new Network on Potato Late Blight in partnership with the Global Initiative for Late Blight (GILB).

Biodiversity and Landscape Complexity

Research about the relationship between biodiversity and ecosystem functioning has been largely triggered by the realization of the rapid lost of biodiversity. The main hypothesis is that loss of species diversity will be detrimental to key ecosystem processes such as primary productivity. Field manipulative experiments such as BIODEPTH in Europe show an overall reduction of aboveground biomass production with loss of species and functional groups (view results). Other studies, however, show no relationship between biodiversity and ecosystem functioning. To further pursue this debate, GCTE has established a network of removal experiments.

Scenarios of changes in biodiversity for the year 2100 can now be developed, based on scenarios of changes in atmospheric CO₂, climate, vegetation, and land use, and the known sensitivity of biodiversity to these changes in terrestrial and freshwater ecosystems. For the terrestrial ecosystems, land-use change will probably have the largest impact on biodiversity followed by climate change, nitrogen deposition, biotic exchange, and elevated CO₂. For freshwater ecosystem, biotic exchange is of much greater importance than in terrestrial ecosystems. The panels show the regional impacts on biodiversity using three different mechanisms by which multiple global change drivers may interact.

GCTE has also developed a Landscape Modeling Shell (LAMOS) to integrated landscape processes and investigate the effects of global change on future landscape structure and functioning. For instances, landscape patterns greatly influence the spread of fire, while changes in fire regime affect landscape patterns. These and other feedbacks involving landscape processes can be investigated with LAMOS.