Abundant fossil plant remains are preserved in the high-latitude late Paleocene Iceberg Bay Formation on Ellesmere Island, Nunavut, Canada. Intact leaf litter lenses and permineralized, in situ logs and stumps offer for the first time an opportunity to determine the structure, biomass, and productivity of a redwood-dominated forest that grew in the polar regions of Nunavut (paleolatitude 75–80° N). Well-preserved fossil tree trunks were excavated to develop equations that describe the height, structure, and mass of the aboveground components of late Paleocene-age (approximately 55.8 to 58.7 million years old) Metasequoia (redwoods) trees. We then combined those data with measurements of the in situ stumps to determine the structure, biomass, and productivity of this polar fossil forest. The height of the canopy trees in the forest was calculated to be 32 ± 2 m. Abundant branch stubs that represent the remnants of living branches were found on a wide range of stem sizes including larger logs from the lower portions of the fossil trees indicating a relatively deep canopy. The branch lengths predicted from allometric relationships developed on modern Metasequoia trees are consistent with the stump spacing measured at Stenkul Fiord. The stem volume equaled 1,632 m3 ha-1 and stem biomass was a minimum of 490 Mg ha-1. Recovery of an incomplete treetop with exposed branch stubs enabled us to make minimum estimates of branch wood and foliar biomass using allometric equations derived from extant Metasequoia glyptostroboides trees in Japan. Estimated stand-level branch biomass was at most 19 Mg ha-1 and standing foliar biomass was estimated to be a maximum of 4 Mg ha-1. We adjusted the derived stemwood biomass estimates to account for a potential bias against sapwood and bark preservation. This adjustment increased our stemwood biomass estimates by 17% to 576 Mg ha-1. Using the annual ring widths of the tree stems, the reconstructed parabolic stems, and wood density of modern Metasequoia, we calculated the annual wood production of the Stenkul Fiord forest to be 3.8 Mg ha-1 yr-1. Assuming the ancient Metasequoia trees were deciduous like their living relatives, the annual aboveground net primary productivity was between 5.8 and 7.8 Mg ha-1 yr-1. These estimated biomass and productivity values fall within the range for those obtained for modern old-growth forests of the Pacific Northwest (USA) and old-growth coastal Cordillera forests of southern Chile and are near the average values for temperate freshwater floodplain forests in North America.
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Vol. 158 • No. 1