A COMPARATIVE ANALYSIS OF MIDDLE- AND HIGH-LATITUDE EARLY EOCENE REDWOOD WETLAND FORESTS

Numerous paleoclimatic reconstructions suggest that the late Paleocene to early Eocene was one of the warmest intervals during the past 65 million years; particularly in the mid- to high-latitudes. I evaluated differences in the ecosystem properties of two early Eocene in situ fossil forests that grew under these greenhouse climate conditions but at different paleolatitudes. I compared a high-paleolatitude (75 to 85 degrees north) fossil forest from the Iceberg Bay Formation, Nunavut, Canada with a lower-latitude (less than 62 degrees N) fossil forest from the Chickaloon Formation in south-central Alaska. An anatomical analysis of fossil stumps and logs indicates that taxodiaceous trees including Metasequoia, and Glyptostrobus grew in peat-forming swamp areas of both fossil forests. Tree densities were slightly higher in the more northerly forest (300 vs. 220 trees per hectare) than in the lower latitude forest but estimated tree heights were similar (32-34 vs. 31 m). Both forests had large amounts of standing biomass (440 to 500 Mg per ha) but estimates of primary productivity for the lower latitude forest was slightly higher (6.2 vs. 5.8 Mg per ha per yr). This may be a function of the age of the forests; the lower latitude forest had younger trees on average than the higher latitude forest (184 vs. 250 yr). Nevertheless, there is a surprising degree of similarity in the composition, structure and biomass and productivity of these forests. This is despite fact that these forests existed in areas that were separated by at least 14 degrees of latitude. These similarities support the notion of similar climate regimes and a reduced latitudinal temperature gradient between the high-middle- and high-latitudes during the early part of the Cenozoic Era.