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

The leaf longevity and seasonal timing of leaf abscission within a plant co mmunity is closely related to climate, a phenomenon referred to as leaf phe nology. In this paper the leaf phenology of some mid-Cretaceous (late Albia n) forests which grew at latitude of 75 degrees S on Alexander Island, Anta rctica, is analysed. Five independent techniques for determining leaf longe vity 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 arauca rian and podocarp conifers, which comprised more than 90% of the canopy-for ming vegetation, were evergreen with leaf retention times in excess of 5-13 years. The application of techniques 3-5 to rare taxodioid conifers indica tes the existence of both evergreen and deciduous habits in this group, whi lst both ginkgos and taeniopterids, which are locally abundant, are interpr eted as possessing a deciduous habit. The polar forests of Alexander Island were therefore dominantly evergreen. Preliminary analysis of five other mi d-Cretaceous polar forests suggests the presence of dominantly evergreen ve getation in Australia and Antarctica, and mixed evergreen-deciduous vegetat ion in Alaska, northern Russia and New Zealand. Cold month mean temperature probably exerted the largest influence on the leaf phenology at each of th ese forest sites.