| Title: | Latest Cretaceous Global Vegetation: Current Understanding and Areas for Future Study |
| Author: | Garland R Upchurch |
| Date Submitted: | 04/30/2002 |
| Address: | Department of Biology, 601 University Drive
San Marcos
Texas
USA
78666
|
| Phone: | (512) 245-3751 |
| Email: | gu01@swt.edu |
| Co-Authors: | Beerling, David J., and Lomax, Barry H., University of Sheffield, UK, d.j.beerling@sheffield.ac.uk, Bette Otto-Bliesner, National Center for Atmospheric Research, ottobli@ncar.ucar.edu |
| Affiliation: | Southwest Texas State University |
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| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725570 |
| Keywords: | vegetation, climate, latest Cretaceous |
| Abstract: | Four major approaches have been used to reconstruct latest Cretaceous vegetation. Biome reconstructions have mapped the distribution of climatically sensitive sediment types, palynomorphs, and plant megafossils, and diagnosed individual biomes using suites of environmental features and patterns of taxonomic co-occurrence. Physiognomic analyses of plant megafossils have used the adaptive characteristics of leaf assemblages and the distribution of life forms to reconstruct vegetation and the climatic parameters under which it grew. Climate modeling studies have used the output of Atmospheric General Circulation Models (or AGCMs) to predict global vegetation and fill in the gaps between data points, using the correlation between modern climatic parameters and the distribution of vegetation. Biogeochemical models have used the output of AGCMs to run process-based models of net primary productivity, leaf area index, and soil carbon.
All four approaches have significant areas of agreement. One area of agreement is the widespread distribution of forest vegetation at high latitudes, which indicates warmer summer and winter temperatures than at present. A second area of agreement is the poleward expansion of cold-sensitive plants and fungi. A third area of agreement is a major (1.5 to 2x) increase in net primary productivity and vegetation carbon relative to the Recent, with a significant fraction of vegetation carbon located at high latitudes. Additional areas of agreement include the occurrence of high soil carbon (i.e., coals) at polar latitudes in the Northern Hemisphere, and large areas of desert and semi-desert vegetation at subtropical latitudes in South America, Africa, and Asia.
All four approaches also have significant areas of disagreement. In equatorial regions, coal distribution and climate model output suggest areally restricted tropical rainforest and areally expanded tropical semi-deciduous forest, while biogeochemical models and patterns of provincialism in palynomorphs suggest a relatively broad equatorial band of dense tropical evergreen forest. At middle latitudes, plant megafossils and palynomorphs indicate a significantly greater poleward expansion of cold-sensitive plants than that predicted by climate models. At a global scale, published estimates of total vegetation carbon based on the biome approach are lower than those based on biogeochemical modeling. Resolution of these and other discrepancies requires expanding the global database of plant megafossils and palynomorphs, especially through the analysis of new floras from poorly understood regions such as the tropics; conducting additional simulations of climate and vegetation using coupled Earth-system models; evaluating uncertainties in paleobotanical data and model output; and better understanding the response of vegetation to Cretaceous levels of atmospheric pCO2. |
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