MIDDLE PLIOCENE VEGETATION - RECONSTRUCTIONS, PALEOCLIMATIC INFERENCES, AND BOUNDARY-CONDITIONS FOR CLIMATE MODELING

The general characteristics of global vegetation during the middle Pli ocene warm period can be reconstructed from fossil pollen and plant me gafossil data. The largest differences between Pliocene vegetation and that of today occurred at high latitudes in both hemispheres, where w arming was pronounced relative to today. In the Northern Hemisphere co niferous forests lived in the modern tundra and polar desert regions, whereas in the Southern Hemisphere southern beech apparently grew in c oastal areas of Antarctica. Pliocene middle latitude vegetation differ ed less, although moister-than-modem conditions supported forest and w oodland growth in some regions now covered by steppe or grassland. Pli ocene tropical vegetation reflects essentially modern conditions in so me regions and slightly cooler-than-or warmer-than-modern climates in other areas. Changes in topography induced by tectonics may be respons ible for many of the climatic changes since the Pliocene in both middl e and lower latitudes. However, the overall latitudinal progression of climatic conditions on land parallels that seen in the reconstruction of middle Pliocene sea-surface temperatures. Pliocene paleovegetation al data was employed to construct a 2 degrees x 2 degrees global grid of estimated mid-Pliocene vegetational cover for use as boundary condi tions for numerical General Circulation Model simulations of middle Pl iocene climates. Continental outlines and topography were first modifi ed to represent the Pliocene landscape on the 2 degrees x 2 degrees gr id. A modem 1 degrees x 1 degrees vegetation grid was simplified and m apped on this Pliocene grid, and then modified following general geogr aphic trends evident in the Pliocene paleovegetation data set.