PALEOECOLOGICAL RECONSTRUCTION OF A MIOCENE HIGH LATITUDE FOREST FROM THE WESTERN CANADIAN ARCTIC

Abundant fossil plant remains are preserved in the mid-Miocene-aged deposits of the Ballast Brook Formation on Banks Island, Northwest Territories, Canada. Intact cones, logs, and stumps preserved in situ as mummified remains present an opportunity to reconstruct the composition, structure, and productivity of a Pinaceae-dominated forest that once grew north of the Arctic Circle (paleolatitude ca. 74 deg. N). We mapped and measured 76 tree stumps exposed in three dimensions on a 0.12 ha coal deposit. Preliminary analysis of wood anatomy and fossil seed cones indicates that Pinus and Picea likely dominated the forest. Stump diameters ranged from 6 cm to 56 cm (average = 30 cm). We utilized allometric relationships we derived for modern Picea growing above the Arctic Circle in the Mackenzie River delta to predict tree height given stump diameters of the fossil forest. Our estimates suggest that the average tree height of the Miocene forest was 14 m and the largest diameter trees were approximately 22 m in height. We used stump diameter data and predicted canopy height to calculate parabolic stem volume and stem biomass for the exposed area of fossil forest. Stem volume equaled 430 m³ ha^-1 and stem biomass (assuming a wood density similar to modern Picea of 450 kg m^-3) equaled 193 Mg ha^-1 . On a stand-average basis, the annual ring width of the stem wood sampled in the field equaled 1.5 mm. Based on this ring width our preliminary estimate for carbon sequestered aboveground as wood in these forests is 3.1 Mg ha^-1 yr^-1. Thus, these were moderate biomass forests with moderate productivity typical of modern cool temperate forests.