Reconstruction of TertiaryMetasequoiaforests. II. Structure, biomass, and productivity of Eocene floodplain forests in the Canadian Arctic

Abstract

Abundant fossil plant remains are preserved in the high-latitude middle Eocene deposits of the Buchanan Lake Formation on Axel Heiberg Island, Nunavut Territory, Canada. Intact leaf litter, logs, and stumps preserved in situ as mummified remains offer an opportunity to determine the structure, biomass, and productivity of two Taxodiaceae-dominated forests that grew north of the Arctic Circle (paleolatitude 75–80°N). We excavated fossil tree trunks and treetops to develop equations that describe the height, structure, and mass of the aboveground components of Eocene-age Metasequoia trees. We combined those data with surveys of in situ stumps to determine the structure, biomass, and productivity of two fossil forests, “N” and “HR.” We calculated a canopy height of 40 ± 3 m for the N forest and 25 m ± 2 m for the HR forest. Buried knots in dissected logs and abundant branch-free bole wood indicate that these were tall, closed-canopy forests. Stem tapers indicate that the overstory was of uniform height. Stem volume equaled 2095 m3 ha−1 and stem biomass was 628 Mg ha−1 in the N forest. Volume and biomass in the HR forest were much smaller, 211 m3 ha−1 and 63.3 Mg ha−1, respectively. We estimated understory tree biomass to be 40 Mg ha−1 in the N forest and 3.5 Mg ha−1 in the HR forest. Recovery of seven fossil treetops with exposed branch stubs enabled us to make estimates of branchwood and foliar biomass using allometric equations derived from modern, plantation-grown Metasequoia glyptostroboides. Estimated stand-level branch biomass was 13 and 6.7 Mg ha−1 in the N and HR forests, respectively. Standing foliar biomass was estimated to be 3.2 and 2.1 Mg ha−1 in the N and HR forests, respectively. Using annual ring widths, the reconstructed parabolic stems, and wood density of modern Metasequoia, we calculated annual wood production to be 2.3 Mg ha−1 yr−1 for the N forest and 0.55 Mg ha−1 yr−1 for the HR forest Assuming that the ancient Metasequoia were deciduous like their living relatives, annual aboveground net primary productivity was 5.5 Mg ha−1 yr−1 for the N forest and 2.8 Mg ha−1 yr−1 for the HR forest. Our estimated biomass and productivity values for N are similar to those of modern old-growth forests of the Pacific Northwest of the United States and old-growth coastal Cordillera forests of southern Chile.

Floral and environmental gradients on a Late Cretaceous landscape

“…Fossil floras that preserve information about vegetational and habitat heterogeneity on a scale of meters to hundreds of meters are known from every interval of geological time since the advent of vascular land plants (e.g., Devonian [Andrews et al 1977]; Carboniferous [Wnuk and Pfefferkorn 1987, DiMichele and Nelson 1989, Gastaldo et al 2004, Oplustil et al 2009]; Permian [Pfefferkorn and Jun 2007]; Triassic [Cu´neo et al 2003, Artabe et al 2007]; Jurassic [Spicer and Hill 1979]; Cretaceous [Cantrill 1996]; and Cenozoic [Gemmill and Johnson 1997, Davies-Vollum and Wing 1998, Williams et al 2003). The fossil record clearly documents changes in ecological strategies and preferences of organisms through time.…”

Isotopic characteristics of canopies in simulated leaf assemblages

“…Fossil assemblages seldom preserve branchless boles, or evidence of tree spacing or branch density associated with canopy density (Secord et al, 2008). While a few exceptional assemblages include large, fleshy fruits (an adaptation to dense canopy) (Tiffney, 1984;Eriksson et al, 2000;Bruun and Ten Brink, 2008;Friis et al, 2011) or in situ litter, logs, and stumps (Williams et al, 2003;DiMichele and Falcon-Lang, 2011), the most common macroscopic plant fossils are leaves and leaf fragments (Ellis et al, 1999). Forest architecture is inferred from leaf fossils by morphologic and taxonomic comparison to extant ecosystems (Upchurch and Wolfe, 1987;Wing et al, 1991Wing et al, , 2000Wing et al, , 2009Wilf, 2000;Johnson and Ellis, 2002).…”

Leaf habit of Late PermianGlossopteristrees from high-palaeolatitude forests

“…Growth chamber experiments and numerical models, however, demonstrate that there is no carbon balance advantage for deciduous trees over evergreen trees grown under a simulated polar photoperiod (Osborne & Beerling 2002;Royer et al 2003Royer et al , 2005, because deciduous trees must annually regrow all leaf tissue, and the carbon source for this new growth must be derived from photosynthate fixed during previous growing seasons (Sauter 1967;Essiamah & Eschrich 1985;Barbaroux & Breda 2002;Damesin & LeLarge 2003). Nevertheless, fossil evidence of trees such as Metasequoia, Larix, Alnus and Betula provides support that deciduous trees dominated the Northern Hemisphere polar regions during the Cenozoic (Wolfe 1980;Greenwood & Basinger 1993;Greenwood 1994;Williams et al 2003Williams et al , 2008Ballantyne et al 2010;Csank et al 2011a,b) and the Cretaceous (Spicer & Parrish 1986;Spicer & Chapman 1990), and they are interpreted to have dominated the Southern Hemisphere polar regions during the Permian and Triassic ( Fig. 1; Gould & Delevoryas 1977;Taylor et al 1992;Francis et al 1993;McLoughlin 1994;McLoughlin et al 1997;Cúneo 1996;McLoughlin et al 2005).…”