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Ecosystem modeling, a pillar of the systems ecology paradigm (SEP), addresses questions such as, how much carbon and nitrogen are cycled within ecological sites, landscapes, or indeed the earth system? Or how are human activities modifying these flows? Modeling, when coupled with field and laboratory studies, represents the essence of the SEP in that they embody accumulated knowledge and generate hypotheses to test understanding of ecosystem processes and behavior. Initially, ecosystem models were primarily used to improve our understanding about how biophysical aspects of ecosystems operate. However, current ecosystem models are widely used to make accurate predictions about how large-scale phenomena such as climate change and management practices impact ecosystem dynamics and assess potential effects of these changes on economic activity and policy making. In sum, ecosystem models embedded in the SEP remain our best mechanism to integrate diverse types of knowledge regarding how the earth system functions and to make quantitative predictions that can be confronted with observations of reality. Modeling efforts discussed are the Century ecosystem model, DayCent ecosystem model, Grassland Ecosystem Model ELM, food web models, Savanna model, agent-based and coupled systems modeling, and Bayesian modeling.
The systems ecology paradigm could not have developed without advances in computer science, chemical analysis, microscopy, remote sensing and telemetry, geographic information systems, and information management systems. In the late 1960s, mainframe computers occupying entire rooms and buildings cranked out calculations at speeds that pale in comparison to today’s smart phones, laptop, and desktop computers. Chemical analyses were accomplished primarily using wet chemistry. The ability to “see” inside soil particles has evolved from the desktop microscope to computer imaging. With modern spectroscopy and imaging both precision and accuracy have advanced exponentially. Remote sensing was conducted using photography from airplanes, towers, and ladders. Now we have high-resolution imaging, and spectral imaging, from satellites, manned aircraft, and drones. Geographic information systems have developed from paper maps to powerful technologies manipulating and displaying massive amounts data on handheld devises, laptops, and desktop computers. Information management has moved from data storage on paper files to digital and searchable storage available from almost anywhere on earth. Now, all of these technologies are interconnected through digital networks used by systems ecologists. Systems ecologists have both adopted and developed new technology and these advances have gone hand-in-hand with conceptual change.
Emerging from the warehouse of knowledge about terrestrial ecosystem functioning and the application of the systems ecology paradigm, exemplified by the power of simulation modeling, tremendous strides have been made linking the interactions of the land, atmosphere, and water locally to globally. Through integration of ecosystem, atmospheric, soil, and more recently social science interactions, plausible scenarios and even reasonable predictions are now possible about the outcomes of human activities. The applications of that knowledge to the effects of changing climates, human-caused nitrogen enrichment of ecosystems, and altered UV-B radiation represent challenges addressed in this chapter. The primary linkages addressed are through the C, N, S, and H2O cycles, and UV-B radiation. Carbon dioxide exchanges between land and the atmosphere, N additions and losses to and from lands and waters, early studies of SO2 in grassland ecosystem, and the effects of UV-B radiation on ecosystems have been mainstays of research described in this chapter. This research knowledge has been used in international and national climate assessments, for example the IPCC, US National Climate Assessment, and Paris Climate Accord. Likewise, the knowledge has been used to develop concepts and technologies related to sustainable agriculture, C sequestration, and food security.
The sixth annual Global Change Institute (GCI) was held in 1993 in Snowmass, Colorado, to evaluate the state of knowledge of the global carbon cycle. As in previous GCIs, an overarching goal was to increase the interdisciplinary communication between scientists in different disciplines. The 1993 GCI focused on those studying the various facets of the carbon cycle, including emissions of carbon dioxide, carbon in the oceans, the role of terrestrial ecosystems and land use, and measurements of carbon dioxide buildup in the atmosphere.
The goal of the institute was in part scientific, and in part to support the then-ongoing assessment of the carbon cycle by the Intergovernmental Panel on Climate Change (IPCC) (Schimel et al., 1995, 1996; Melillo et al., 1996). The IPCC had assessed the state of knowledge concerning the carbon cycle in its 1990 and 1992 reports (Watson et al., 1990, 1992); however, its 1994 and 1995 reports required a more in-depth analysis. The need for greater depth was driven by the 1992 United Nations Framework Convention on Climate Change (FCCC). Article 2 of the FCCC states as a primary objective that countries should seek to stabilize the concentrations of greenhouse gases in the atmosphere in order to stabilize future climate (within the limits of natural variability).
We compared four adjacent soil plots in an effort to determine the effect of land use on soil carbon storage. The plots were located at the High Plains Agricultural Research Laboratory near Sidney, Nebraska. We measured 14C, total carbon, total nitrogen and 137Ce to determine the size and turnover times of rapid and stable soil organic matter (SOM) pools, and their relation to land-use practices. Results were consistent with the model produced by Harrison, Broecker and Bonani (1993a) in that the 14C surface soil data fell on the time trend plots of world 14C surface soil data, indicating that the natural sod and non-tilled plots had a rapidly turning over SOM pool, comprising ca. 75% of surface soil carbon, and the tilled plots had a rapidly turning over SOM pool, comprising only 50% of surface soil carbon.
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