The synthesis of available knowledge on the biodiversity and ecosystem functioning below surface became an international scientific priority in 1992 as a result of a workshop on biodiversity and ecosystem functioning (Schulze & Mooney 1994). In 1995, a SCOPE (Scientific Committee on Problems in the Environment) Committee on Soil and Sediment Biodiversity and Ecosystem Functioning (SSBEF) began to evaluate available data with the goal of providing policy makers with the scientific tools and information needed to promote sound management. How did this committee proceed to build the foundation for this book?
Through unprecedented collaboration between 70 international taxonomists and ecosystem scientists with expertise in soils, freshwater sediments, and marine sediments, the SSBEF committee developed state-of-the-art interdisciplinary syntheses and identified research and policy areas that need the most urgent attention. The committee held three extremely successful international workshops (see the SCOPE SSBEF committee publication list at the back of this volume, and summaries at the website http://www.nrel.colostate.edu/soil/SCOPE/scope.html). The workshops have resulted in 41 publications in journals read by scientists, managers, and policy makers. Additionally, the workshop syntheses have helped launch a new integrative discipline that crosses traditionally isolated disciplines (e.g., taxonomy, biogeochem-istry, ecology), management, and domains (terrestrial, atmospheric, freshwater, and marine). This new scientific approach has contributed data to advance a more integrated and holistic understanding of Earth-system functioning and provides a foundation for this book. The SCOPE SSBEF syntheses identified major gaps in knowledge and research priorities in three overarching areas:
1. The importance of soil and sediment biodiversity and ecosystem functioning within domains (soils, freshwater sediments, marine sediments). Keystone functional groups (a group of species that has a much greater impact on an ecosystem process through impact on trophic relations than would be expected from its biomass) were identified within each domain. Comparisons among all domains revealed that, in general, the keystone ecosystem functions were strikingly similar in all domains (Table 1.3), although the taxa involved were often remarkably different. The diversity of functions performed may be more important than the diversity of organisms for sustaining ecosystem processes. Thus, there appear to be universally important functions performed across all soil and sediment domains, and these contribute to vital ecosystem goods and services (Table 1.4). For example, in all domains many species are part of a complex food web that breaks down organic matter—by shredding, ripping, or dissolving it—and thus recycles soil nutrients to living plants and releases carbon dioxide and sequesters carbon (Table 1.3). Species in both soils and sediments filter particles from water and influence its flow, in turn cleansing and purifying water and playing a pivotal role in nutrient cycling and in the Earth's hydrological cycle.
2. The importance of soil and sediment biodiversity and ecosystem functioning across domains. Collaboration of scientists from all domains was crucial to elucidating the understanding that below-surface species and the processes they regulate do not operate in just one domain (e.g., exclusively in soils, freshwater sediments, or marine sediments). These species play a critical role by crossing and connecting domains, below and above surface, and thus regulating essential global cycles that contribute to the stabilization of Earth's climate and the maintenance of functioning ecosystems. Moreover, human disturbances in one domain can have cascading effects onto other domains. The SSBEF review committee found that integrated knowledge, research, and management of the domain interfaces was severely lacking. They set this area of interface exploration as a major research priority in order to maintain the high diversity and important functions in soils and sediments.
3. Threats to soil and sediment biodiversity and their functioning. The SSBEF workshops revealed that across all domains, global change poses a significant threat to below-surface biodiversity and the ecosystem functions they regulate. There was evidence across domains that land use change (including deforestation, overfishing, damming of rivers, agricultural intensification, pollution, and increased trampling), invasive species, and climate change can shift species composition, eliminate species, and reduce diversity at local to regional scales (Lake et al. 2000; Smith et al. 2000; Wolters et al. 2000; Wall et al. 2001b). The loss of populations and species at these local and regional scales threatens biodiversity, since it reduces genetic diversity, foreclosing opportunities for evolution and homogenizing biodiversity across the landscape. Whether species become globally extinct depends on the geographical extent of their range relative to that of the disturbance. But highresolution data on the effects of a perturbation on soil and sediment biodiversity at large biogeographic scales is incomplete and was identified as another research priority. The SSBEF committee also determined that across all domains, current and predicted global change effects on below-surface biodiversity are, and will be, manifested largely through changes linked to above-surface habitats and biodiversity. These above-surface changes will transform the below-surface physical-chemical environment, alter the transfer of nutrients and other resources belowground, and decouple species-specific interactions. These transformations may, in turn, have multiple, significant consequences for above-surface habitats and for their biodiversity and ecological processes.
Specific information was lacking on the vulnerability to human activities of the most important below-surface taxa and functions and their linkages above surface. How this vulnerability might be ameliorated by management options was considered an urgent priority for further research and synthesis. The workshops and syntheses of the SSBEF committee have advanced a paradigm shift in understanding biodiversity in soils and sediments. Scientists have acquired a more complete picture of these domains, especially the keystone taxa and functions, and are beginning to learn to what extent they are being, and may continue to be, disrupted and impaired by global change.
This improved, holistic understanding of below-surface biodiversity and of the linkages to organisms both above-surface and among domains was necessary before we could proceed toward addressing questions on the critical taxa, their ecosystem functions, habitats, biogeographical occurrence, and vulnerabilities.
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