CBC News NB Wed, 02 July 2003 LONDON - Secret surrounds leaf fall in ancient polar forests Researchers have dealt a blow to a long-held theory on why leaf-dropping trees were preferred to evergreens in ancient polar forests. During much of the past 250 million years, the poles were devoid of ice and deciduous trees dominated much of the area. Back then, the polar climate resembled that of the Mediterranean today. Scientists are trying to figure out why ancient forests were deciduous According to the carbon loss hypothesis, leafless branches had an advantage over evergreens in the continuous darkness and warmth of the polar forests, said Penn State University geoscientist Dana Royer. The idea is deciduous trees flourished at the poles because they did not maintain a respiring leaf canopy during the dark months. Canopies lose carbon through respiration during the dark winter months. Royer and biologists Colin Osborne and David Beerling of Sheffield University in the United Kingdom tested the leaf shedding hypothesis by growing modern descendents of the trees under growing conditions of an ancient forest at 69 degrees latitude. The researchers grew deciduous gingko, dawn redwood and bald cypress saplings for three years. Two evergreens, sequoia and southern beech, were also tested. The team monitored the amount of leaf litter and carbon lost from respiration. Computer simulations extrapolated the results to a mature forest. They concluded leaf shedding was a "false economy": the amount of carbon lost would have far outweighed that burned as fuel by an evergreen canopy during a dark, polar winter. The modelling suggests that "the cost of producing a deciduous canopy of leaves remains more than twice that incurred by evergreen trees," the researchers wrote in Thursday's issue of the journal Nature. The researchers suggest scientists should focus on alternative explanations, such as water supply, soil fertility or the chilling effects of low temperatures.