Document: BEN-3-41-18

Composition, structure, dynamics, biomass and climate of Eocene fossil forests, Canadian High Arctic.

LEPAGE, B.A.* ¹, C.J.WILLIAMS ¹, A.H.JAHREN ², A.H.JOHNSON ¹ and D.R.VANN ¹

University of Pennsylvania, Philadelphia, PA 19104 USA ¹
Johns Hopkins University, Baltimore, MD 21218 USA ²

Abstract:
Remarkable preservation of 45 million-year-old forests on Axel Heiberg Island, Canadian High Arctic allows the use of standard field measurements to determine forest composition, architecture, dynamics, and biomass. The taxonomy and systematics of this middle Eocene flora has been studied for a dozen years, but the basic ecological attributes of these forests and the climate under which they grew were poorly understood. Stumps, boles, litter, roots, seeds and soils are preserved as intact, in situ, mummified remains and provide a unique opportunity to reconstruct aspects of this ancient ecosystem from field measurements. The productivity, stem volume and biomass for a 2227 m² area of the fossil forest were previously estimated to be ca. 1200 gm/m²/yr, 946.1 m³/ha and 255 Mg/ha respectively. These estimates are comparable to temperate old-growth forests. In addition, the forest canopy was inferred to be open with its height estimated to be ca. 16 m. The results of our study indicate that the forest was a minimum of 33 m tall, closed canopy, with stem volume of 2190 m³/ha and a stem biomass of 591 Mg/ha. The growth strategy of these fossil Metasequoia-dominated forests is consistent with that of modern plantation-grown Metasequoia forests in Japan. Carbon isotopic analyses were performed on a number of Metasequoia individuals and on paleosol organic matter from every plant-bearing horizon exposed at the fossil forest locality. The ¹³C for fossil Metasequoia ranged from -20.5 to -23 and indicates that the tissues were isotopically homogenous. Moreover, the fossil ¹³C values are high compared to ca. -25 seen in extant Metasequoia. The ¹³C of the middle Eocene atmosphere was quantitatively assessed to be ca. -5.5 , which allowed calculation of the ratio of intracellular (P_i) to ambient (P_a) carbon dioxide concentrations for fossil (P_i/P_a = 0.47 0.56) and extant (0.56) Metasequoia. The values seen in the fossil Metasequoia suggest a higher water use efficiency for the genus relative to that seen in extant Metasequoia.

Keywords: Cenozoic, conifer, Metasequoia, stable isotope, Taxodiaceae, Tertiary

This abstract is being presented at: 4:45 PM in session:
Oral Session #32: Paleoecology.