National Academies Press: OpenBook

Effects of Past Global Change on Life (1995)


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Suggested Citation:"INTRODUCTION." National Research Council. 1995. Effects of Past Global Change on Life. Washington, DC: The National Academies Press. doi: 10.17226/4762.
Page 156

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THE LATE CRETACEOUS AND CENOZOIC HISTORY OF VEGETATION AND CLIMATE AT NORTHERN AND 156 SOUTHERN HIGH LATITUDES: A COMPARISON 9 The Late Cretaceous and Cenozoic History of Vegetation and Climate at Northern and Southern High Latitudes: A Comparison Rosemary A. Askin University of California, Riverside Robert A. Spicer Oxford University ABSTRACT The Late Cretaceous and Cenozoic high latitude land vegetation bequeathed a sensitive paleobotanical and palynological record of regional and global environmental change. Foliar physiognomy provides the most reliable indicators. This record is frequently available for northern localities, augmented by wood and palynomorph data. Southern data are provided mainly by palynomorphs, with some foliar, cuticular, and wood information. The northern high latitude vegetation was mainly deciduous, whereas evergreen taxa locally predominate in the south. Major northern clades were all derived from lower latitudes; in contrast, Antarctica was a center of evolutionary innovation and dispersal. Differences in northern and southern vegetation are a function of continental configurations, interrelated with continentality (winter-summer temperature range), seasonality, moisture/aridity regimes, sea-level cycles, and overprinted by biotic stress or selective mechanisms. Vast land areas encircled the North Pole (to within 85°N), enhancing climatically driven northward and southward migrations, whereas an Antarctic continent continuously occupied the South Polar latitudes, had relatively restricted dispersal corridors, and became increasingly isolated as the other Gondwana fragments spread northward. INTRODUCTION Fossils of plants that lived at high latitudes provide a sensitive and unparalleled record of the complex interplay of global climatic change and polar conditions through time. High latitude plants, presently portrayed by extant polar desert, tundra, and taiga floras, require adaptations for stringent "icehouse" conditions. An icehouse world is, however, infrequently encountered in earth history. More typical "greenhouse" conditions necessitate other strategies for plant survival (Spicer, 1989a; Spicer and Chapman, 1990). In the Mesozoic and Cenozoic greenhouse world, forests thrived near the poles despite the seasonal stress of polar light cycles (the near congruity of rotational and magnetic poles is assumed here).

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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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