Permian polar forests: deciduousness and environmental variation

Abstract

Forests are expected to expand into northern polar latitudes in the next century. However, the impact of forests at high latitudes on climate and terrestrial biogeochemical cycling is poorly understood because such forests cannot be studied in the modern. This study presents forestry and geochemical analyses of three in situ fossil forests from Late Permian strata of Antarctica, which grew at polar latitudes. Stem size measurements and stump spacing measurements indicate significant differences in forest density and canopy structure that are related to the local depositional setting. For forests closest to fluvial systems, tree density appears to decrease as the forests mature, which is the opposite trend of self-thinning observed in modern forests. We speculate that a combination of tree mortality and high disturbance created low-density mature forests without understory vegetation near Late Permian river systems. Stable carbon isotopes measured from permineralized wood in these forests demonstrate two important points: (i) recently developed techniques of high-resolution carbon isotope studies of wood and mummified wood can be applied to permineralized wood, for which much of the original organic matter has been lost and (ii) that the fossil trees maintained a deciduous habit at polar latitudes during the Late Permian. The combination of paleobotanical, sedimentologic, and paleoforestry techniques provides an unrivaled examination of the function of polar forests in deep time; and the carbon isotope geochemistry supplements this work with subannual records of carbon fixation that allows for the quantitative analysis of deciduous versus evergreen habits and environmental parameters, for example, relative humidity.

Leaf habit of Late PermianGlossopteristrees from high-palaeolatitude forests

“…A sedimentological, stratigraphic, and palaeoforestry analysis for the localities was presented by Gulbranson et al (2012), but the salient results are summarized here to provide a palaeoenvironmental context for the studied wood specimens. The three fossil forest localities are found in channel proximal floodplain facies (Graphite Peak and Wahl Glacier), and distal floodplain or marginal lacustrine facies (Mt.…”

“…Therefore, the δ 13 C value patterns of evergreen tree rings can be modified by variations in meteorological conditions that affect the balance of photosynthetic assimilation and the loss of water via stomatal conductance during the growing season (Livingston & Spittlehouse 1996;Walcroft et al 1997;Barbour et al 2002), which is consistent with the hypothesis developed by Francey & Farquhar (1982) to explain seasonal δ 13 C variation in tree rings. Gulbranson et al 2012) showing tree positions and average tree heights for Mt. Achernar and Wahl Glacier, and tree height estimates for each tree at the Graphite Peak fossil forest.…”

Highly productive polar forests from the Permian of Antarctica

“…16 woody material that is preserved in the Buckley Formation, and the presence at Lamping Peak of Glossopteris as the only leaf type and of Vertebraria, we follow previous workers (e.g., Gulbranson et al, 2012;Gulbranson et al, 2014) and interpret Lamping Peak forests to have been composed of trees bearing Glossopteris leaves.…”

“…The Permian sequence consists of: 1) glacigenic, primarily glacial marine and glacial lacustrine deposits recording Gondwanan glaciation (Pagoda Formation, Isbell et al, 1997;; 2) shale and interbedded sandstone deposited in a large post-glacial lake or series of lakes filled by deltaic sediments (Mackellar Formation and lowermost Fairchild Formation, Miller, M.F., et al, 2010); 3) crossbedded sandstone lacking plant fossils deposited in braided stream channels (bulk of Fairchild Formation, Barrett et al, 1986); and sandstone, siltstone, shale and coal deposited in braided stream systems (Buckley Formation, Isbell, 1990;Isbell et al, 1997;Gulbranson et al, 2012Gulbranson et al, , 2014. The amount of plant material and the thickness and extent of coal increases upward within the Buckley Formation.…”

Lonchiphyllum aplospermum gen. et sp. nov.: An Anatomically Preserved Glossopterid Megasporophyll from the Upper Permian of Skaar Ridge, Transantarctic Mountains, Antarctica

“…Local stratigraphie and sedimentologic analysis has not been carried out at Skaar Ridge, but contemporaneous deposits of in situ forests in the Beardmore Glacier region reveal fossils preserved in low-energy environments such as floodplains, channel margins, abandoned channels/backswamps, and lake margins (Gulbranson et al 2012). The abundance of permineralized leaf mats at Skaar Ridge suggests that they were deposited in a lake margin or an abandoned channel because the fine detail preserved in the fossils indicates that the peat was not transported far before fossüization.…”