National Academies Press: OpenBook

Effects of Past Global Change on Life (1995)


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Suggested Citation:"SUMMARY AND IMPLICATIONS." National Research Council. 1995. Effects of Past Global Change on Life. Washington, DC: The National Academies Press. doi: 10.17226/4762.
Page 149

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THE RESPONSE OF HIERARCHIALLY STRUCTURED ECOSYSTEMS TO LONG-TERM CLIMATIC CHANGE: A CASE 149 STUDY USING TROPICAL PEAT SWAMPS OF PENNSYLVANIAN AGE Figure 8.10 Comparison of three climate curve diagrams. The Winston and Stanton (1989) curve is based on abundances in Appalachian basin coals of plants thought to be climatically diagnostic; the Cecil et al. (1985) curve is based on geochemical characteristics of coals and associated rocks in the Appalachian basin; and the Phillips and Peppers(1984) curve is a smoothed logarithmic curve plotting the distribution of coal resources in North America. Examination of compression-impression floras from the Pennsylvanian and Permian suggests a similar pattern. There are no climate curves for the Stephanian and Early Permian. However, analyses of Pfefferkorn and Thomson (1982), Ziegler (1990), and DiMichele and Aronson (1992) indicate discontinuous vegetational changes, ultimately resulting in a tropical vegetation with highly xeromorphic aspect. It appears that lowland-wetland vegetation persisted as a unit into the Early Permian and was replaced rather than displaced by what came to be the "Mesophytic" flora (Knoll, 1984; DiMichele and Aronson, 1992). The evidence of increasingly seasonally dry climate into the Early Permian is consistent with both the vegetational and the morphological patterns. The compression floras also suggest a level of organization above that of the landscapes observed in coal swamps, at which taxonomic composition is highly conserved. It may be at this level that the ultimate effect of evolutionary ancestry is manifested. SUMMARY AND IMPLICATIONS The relationships of turnover at the landscape, habitat and species levels in coal swamps are summarized in Figure 8.11. Turnovers in landscape organization—breakpoints—appear to be a consequence of changes in the proportions of several major types of intraswamp habitats. Turnover in the species composition of swamps correlates with turnover at the landscape level. Consequently, the reshuffling of habitat proportions may reflect periods of intraswamp disruption and dislocation, leading to increased, but usually not catastrophic, levels of species extinction. Species replacements across breakpoints are on strongly ecomorphic themes and, therefore, occur largely within the confines of habitats. For this reason, species turnover does not appear to be the major underlying mechanism of change at the landscape level. Intervals of very high extinction result in the loss of framework ecomorphic species. The result is the breakdown of intrahabitat spe

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What can we expect as global change progresses? Will there be thresholds that trigger sudden shifts in environmental conditions—or that cause catastrophic destruction of life?

Effects of Past Global Change on Life explores what earth scientists are learning about the impact of large-scale environmental changes on ancient life—and how these findings may help us resolve today's environmental controversies.

Leading authorities discuss historical climate trends and what can be learned from the mass extinctions and other critical periods about the rise and fall of plant and animal species in response to global change. The volume develops a picture of how environmental change has closed some evolutionary doors while opening others—including profound effects on the early members of the human family.

An expert panel offers specific recommendations on expanding research and improving investigative tools—and targets historical periods and geological and biological patterns with the most promise of shedding light on future developments.

This readable and informative book will be of special interest to professionals in the earth sciences and the environmental community as well as concerned policymakers.

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