ENGLISH oaks reach up to three times their normal height when grown in high concentrations of carbon dioxide, the principal gas responsible for global warming, according to new research.
Oaks grown in double the concentrations of carbon dioxide found in the atmosphere grow 12 feet after only two years - three times the height of those grown in control plots. The trees also grew outwards at previously unheard-of rates, putting on twice as much leaf, stem and root as normal.
Researchers predict that the mature English oak (quercus robur) could double its average height of 100ft by the end of the next century if, as expected, carbon dioxide levels in the atmosphere double because of rising fossil fuel emissions.
Enhanced levels of carbon dioxide in the atmosphere have long been expected to mean that more carbon is available for plants to photosynthesise but this is the first time that the effect on Britain's native hardwoods has been quantified.
The discovery was made by scientists at Horticulture Research International, a privatised Ministry of Agriculture laboratory at East Malling, Kent. It has spent two years on a study backed by the Government and the European Union into the possible impact of the greenhouse effect on Europe's forests.
Acorns grown in enhanced carbon dioxide levels have also been found to produce a higher proportion of viable seedlings.
Dr Chris Atkinson, project leader, said: "I have to say these results surprised us. These trees are now leafing out in their third year and they are extremely tall.
"There was a lot of information before which said that you get these effects but they do not last. We were surprised that after the first year the trees were still responding positively."
The effects were particularly marked in oak. Cherry, which was also included in the experiment, showed early signs of enhanced growth but the effects tailed off after four months.
Though oak trees growing in windy conditions out of doors would not grow as tall as those in the calm conditions of a greenhouse, Dr Atkinson said they would be likely to put on more girth instead.
The implications for foresters and nurserymen are dramatic, with oaks growing to maturity faster.
Nurserymen could use carbon dioxide to bring on slow-growing hardwoods in the greenhouse. These would have to be planted out during the autumn or winter because bringing the trees into normal carbon dioxide concentrations has been shown to cause leaves to curl up or drop.
The discovery also raises the possibility that forests could be used to mop up carbon dioxide freed by burning fossil fuels, though Dr Atkinson said this would not account for a significant proportion of the billions of tons emitted each year.
More disturbingly, the findings are likely to show that chopping down tropical forests and other fast-growing forests, such as the rainforests of the Pacific seaboard of America and Canada, could be even more damaging to the climate than previously believed.
Dr Atkinson emphasised that the greenhouse effect could also impose limiting factors upon the growth of trees by causing drought. The enlarged trees, grown in increased levels of carbon dioxide, might be expected to be more vulnerable to drought than at present because their "pipework" would be more extended.
The overall condition of Britain's trees has improved for the second year running thanks to a wet winter last year and adequate summer rainfall, the Forestry Commission said yesterday.
Beeches were in a better condition than at any time for eight years and although oaks remained in a relatively poor condition, they showed the greatest improvement.
