24 April 2006The Independent
It is not only in the icefields and glaciers of the Arctic, visited in a blaze of publicity last week by the Tory leader David Cameron, that the signs of global warming can be found.
Here comes a different-looking British countryside; clear evidence of climate change affecting the numbers and range of Britain's wild flowers has been found for the first time.
In some cases, the movement has been a positive one. Two of Britain's loveliest wild orchids have shown surprising increases over the past two decades, and leading botanists believe that the warming climate is responsible.
Both the bee orchid and the pyramidal orchid have virtually doubled in frequency since 1987, according to a new survey carried out by the Botanical Society of the British Isles (BSBI) in association with Plantlife, a wild-flower charity.
Until now, the effects of global warming on Britain's plant kingdom have only been detected in phenology - the timing of appearing, leafing and flowering. For example, oak trees are coming into leaf as many as 10 days earlier than they were 30 years ago, and spring flowers such as snowdrops are blooming as early as December.
But the new study - the BSBI Local Change Survey - clearly shows that some species are now increasing in numbers and frequency of occurrence in a way that is consistent with steadily rising temperatures.
The survey was carried out by BSBI volunteers who examined changes in the British flora since 1987 in 800 two-kilometre grid squares, or tetrads, across the country, and the increase in the two orchids was perhaps the most remarkable result.
Both are especially beautiful flowers. The pyramidal orchid looks something like a purplish-pink ice-cream cone, while the quite scarce bee orchid is one of the most spectacular of all Britain's wild plants: it has a flower spike whose blooms are astonishingly lifelike imitations of bumble bees. Wild bees see them and attempt what naturalists delicately refer to as pseudo-copulation; they get covered in pollen in the process, and the next time they attempt the business with another plant, they accidentally pollinate it.
The survey found impressive increases in both species. The bee orchid was found in 42 of the tetrads surveyed: there were 14 sites where it was still present from 1987, three where it had been lost, but 25 where it was new. Similarly, the pyramidal orchid was found in 43 tetrads: there were 17 continuous sites, three losses, and 23 new sites.
Both plants have doubled in numbers and the BSBI considers climate change is very probably the reason for the increase.
Over the period, Britain has definitely become a warmer place: the mean central England temperature for 1987 was 9.05C, while that for 2004 was 10.51C. Between 1900 and 1987, fewer than one year in six had a mean temperature above 10C, but nine of the 11 years between 1994 and 2004 exceeded this threshold.
The two orchids are well-placed to take advantage of such a significant shift in temperatures because they are mobile, with tiny seeds which are blown on the wind. It is thought that hotter summers, which may lead to grasses and other vegetation dying back, would offer more patches of earth where the seeds could become established.
Other plants with similarly mobile tiny seeds or spores, such as ferns, are also showing increases, the survey found. The hart's-tongue fern, for example, is showing a 25 per cent growth in population, moving from the warmer west of the country to the once-cooler east, and spreading out of sheltered gullies into woodlands.
More increases that may be consistent with a warming climate have been found in plants that specialise in growing on waste places, such as square-stalked willowherb and prickly lettuce.
"When we started this survey, most of us in the BSBI did not think we would see evidence of climate change happening yet, but we were struck by the results," said Michael Braithwaite, one of the organisers. "The trend in species such as the two orchids is strong. To find that they had, to all intents and purposes, doubled over 18 years was a great surprise."
Climate change is likely to produce losers as well as winners in Britain's native flora - flowers of the mountains and cooler places are expected to decline - but the survey did not pick up as much negative evidence.
However, there is one candidate for global warming victim, and this is once again an orchid: the lesser butterfly orchid.
This is a species of northern Europe, which tends to grow on the edges of heaths and moorlands. Over the survey period, a 50 per cent decline in it has been recorded, although the likelihood of this being due to global warming is less certain.
