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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.
