National Academies Press: OpenBook

Effects of Past Global Change on Life (1995)

Chapter: Resolution at 100- to 104-yr Time Scales: Habitats and Species Assemblages

« Previous: Clastic Wetlands
Suggested Citation:"Resolution at 100- to 104-yr Time Scales: Habitats and Species Assemblages." National Research Council. 1995. Effects of Past Global Change on Life. Washington, DC: The National Academies Press. doi: 10.17226/4762.
Page 138

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THE RESPONSE OF HIERARCHIALLY STRUCTURED ECOSYSTEMS TO LONG-TERM CLIMATIC CHANGE: A CASE 138 STUDY USING TROPICAL PEAT SWAMPS OF PENNSYLVANIAN AGE the moist lowlands (DiMichele et al., 1986, 1991). This is a consequence of the edaphic barriers created by the physical character of swamps. Overlap is greatest among medullosan pteridosperms, many of which apparently colonized those parts of peat swamps subject to flood and fire disturbance, areas with the greatest similarity to parts of the clastic wetlands. COAL SWAMPS AS HIERARCHICALLY ORGANIZED SYSTEMS Coal swamps were an integral part of Carboniferous lowland environments and have become the epitome of the "coal age" as generally presented to nonspecialists. In fact, coal swamps represent a special subset of the total range of environments existing during that time. Although this subset is more diverse and heterogeneous than dioramas depict, it constitutes a distinctive basis for making ecological comparisons through Late Carboniferous time. Peat-forming environments are a recognizable environmental subset, providing a taphonomically comparable basis for pattern analysis. In addition, the system was semiclosed to species introduction because of the edaphic constraints imposed on plants by the usually saturated peat substrate. This limitation increases the resolution of ecological patterns through time. The effort of dozens of paleobotanists, for more than a century, has provided the taxonomic and morphological baseline for us to generate a large quantitative data base from approximately 40 coals in western Europe and the United States (Figure 8.2). Organization of Coal-Swamp Ecosystems The organization of coal-swamp ecosystems is complex, and can be examined at a variety of spatial and temporal scales (Figure 8.3). Each of these scales reveals different elements of the overall organizational hierarchy. In most instances the relationships of organizational patterns and dynamics at different levels are more clearly seen when a larger view of the system is taken. Resolution at 100- to 104-yr Time Scales: Habitats and Species Assemblages Coal-ball occurrences vary from scattered specimens to distinct zones or massive aggregates, in situ within coal seams (Figure 8.1). Although many deposits are locally extensive, distinct zones of coal balls can be followed laterally no more than a few meters in most instances. Such "zones" of coal balls can be treated as the litter layer of a single forest stand, preserving a time period of <1 yr (instantaneous events such as fires preserved in fusain layers) to 100 yr. Study of the species composition and Figure 8.2 Global paleogeography during the Late Carboniferous. Coal balls come from the shaded area of the tropical Euramerican subcontinent. Map adapted from 1988 version of Terra Mobilis produced by C. R. Scotese and C. R. Denham. Figure 8.3 Spatial and temporal scales of resolution available from coal-ball data analysis. SQ.M.= square meters. Small capitals refer to fossil samples, large, bold capitals refer to inferences made from fossil samples.

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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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