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Department of Biology, Royal Holloway and Bedford New College, Egham Hill, Egham, Surrey TW20 OEX, UK
The existence of a temperate Antarctic flora in the Permian, Mesozoic and early Tertiary poses a number of problems that are not soluble by reference to any environmental situation obtaining at the present day (i.e. in which plants live in a regime where a warm summer is followed by a winter without sunlight).
Certain characteristics of the polar climate during a number of geological periods can be deduced from the remains of forests which grew at very high latitudes where tree growth cannot take place at the present day. The demands of tree growth of the order of 3 to 4 mm increase in trunk radius each year are such that an input of light energy of at least 3000 MJ m–2a–1 would be necessary.
Light energy inputs of this magnitude have been measured at very high latitudes in both North and South polar regions and it would appear that polar forest growth would be possible today if the ambient temperatures were sufficiently raised above their present levels. It is also significant that the forest productivity of about 10 t ha–1 as estimated for the Lower Cretaceous forest on Alexander Island (Palaeolat. 70°S), is a terrestrial productivity that is only matched at the present day in a variety of temperate and subtropical regions of the world.
The evolution of photoperiodic ecotypes in tree species must have facilitated the colonization of polar regions by tree varieties adapted to make all of their annual growth during the long summer light period. There is evidence also that these photoperiodic ecotypes have a high rate of cambial activity concentrating the more rapid growth of wood into the polar summer.
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  I. Poole and D. J. Cantrill Cretaceous and Cenozoic vegetation of Antarctica integrating the fossil wood record Geological Society, London, Special Publications, 2006; 258: 63 - 81. [Abstract] [PDF]
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