Leaf phenology of some mid-Cretaceous polar forests, Alexander Island, Antarctica

Abstract

The leaf longevity and seasonal timing of leaf abscission within a plant community is closely related to climate, a phenomenon referred to as leaf phenology. In this paper the leaf phenology of some mid-Cretaceous (late Albian) forests which grew at latitude of 75°S on Alexander Island, Antarctica, is analysed. Five independent techniques for determining leaf longevity are applied to the fossil remains of each of the canopy-forming trees. These techniques utilize: (1) the anatomical character of growth rings in trunk woods, (2) leaf trace persistence in juvenile branch and stem woods, (3) leaf physiognomy, (4) comparison with nearest living relatives, and (5) leaf taphonomy. The application of techniques 1-5 suggests that the araucarian and podocarp conifers, which comprised more than 90 % of the canopy-forming vegetation, were evergreen with leaf retention times in excess of 5-13 years. The application of techniques 3-5 to rare taxodioid conifers indicates the existence of both evergreen and deciduous habits in this group, whilst both ginkgos and taeniopterids, which are locally abundant, are interpreted as possessing a deciduous habit. The polar forests of Alexander Island were therefore dominantly evergreen. Preliminary analysis of five other mid-Cretaceous polar forests suggests the presence of dominantly evergreen vegetation in Australia and Antarctica, and mixed evergreen-deciduous vegetation in Alaska, northern Russia and New Zealand. Cold month mean temperature probably exerted the largest influence on the leaf phenology at each of these forest sites.

Leaf habit of Late PermianGlossopteristrees from high-palaeolatitude forests

“…Direct evidence of leaf longevity can be determined by assessing whether leaf traces found in wood terminate within a single growth ring (deciduous) or transcend several annual increments of growth (evergreen) (Eames & McDaniels 1947;Falcon-Lang & Cantrill 2001). Such palaeobotanical inferences of leaf longevity, however, are limited in deep time, because of the low probability of preservation, taphonomy of the fossils and detection of such anatomy.…”

“…Because CSDM was initially created to determine earlywood-latewood boundaries (Creber & Chaloner 1984), the potential for inaccuracy of this method in establishing fundamental plant physiological traits would be expected to carry over in the use of CSDM to provide leaf longevity determinations. Accurate results of CSDM analysis applied to extant wood (Falcon-Lang & Cantrill 2001), however, suggest that there is probably a signal of leaf longevity expressed by this proxy, but the application of this proxy to fossil specimens should be aided by the use of independent determinations of leaf longevity until more refinements are made to the by guest on April 27, 2019 https://jgs.lyellcollection.org/ Downloaded from LEAF HABiT OF GLOSSOPTERiD FORESTS 503 CSDM approach that provide accurate determinations of earlywood-latewood boundaries. The microsamples used for stable isotope analysis reflect an average over c. 100-500 µm sample thicknesses, which correspond to c. 10-50 tracheid cells, thus wood distortion might be less well expressed in the isotopic data.…”

“…Two principal factors limit the accumulation of plant biomass: stress (lowers productivity) and disturbance (destroys biomass) (Grime 1977). The dominant stresses expected for these forests are seasonal variations in temperature (Falcon-Lang & Cantrill 2001), which can control the length and timing of the growth season and metabolic rates, and canopy-induced light limitation, which can affect the ability of an organism to compete for the same quanta of light or nutrients. We interpret that erosion and fire were important disturbance processes.…”

“…1; Gould & Delevoryas 1977;Taylor et al 1992;Francis et al 1993;McLoughlin 1994;McLoughlin et al 1997;Cúneo 1996;McLoughlin et al 2005). Evergreen trees belonging to Araucariaceae and Podocarpaceae, on the other hand, dominated the Southern Hemisphere polar regions during the Cretaceous and Jurassic (Cantrill 1991(Cantrill , 1992Pole 1999;Falcon-Lang & Cantrill 2001). These deep-time examples of polar ecosystems suggest that there may have been an adaptation of leaf longevity to high-latitude ecosystems during greenhouse intervals; however, the mechanism for determining the dominance of a particular type of leaf habit remains poorly defined.…”

Carbon loss by deciduous trees in a CO2-rich ancient polar environment

“…1, [4][5][6][7] argues that it was an adaptation to photoperiod, allowing the avoidance of carbon losses by respiration from a canopy of leaves unable to photosynthesize in the darkness of warm polar winters [8][9][10][11] . Here we test this proposal with experiments using 'living fossil' tree species grown in a simulated polar climate with and without CO 2 enrichment.…”