British plants are coming into flower earlier as temperatures rise, according to a study published today which is based on nature records dating back 250 years.
The research, which draws on observations from members of the public, reveals that each 1C rise in temperature has seen blooms appearing five days earlier.
It also shows that despite this year's late signs of spring, caused by a cold winter, long term changes in temperature are taking place.
The change has been greatest in the past 25 years, with flowers coming out between two and 12 days earlier in the past quarter century than in any previous 25-year period.
These latest findings echo a study published in February in the journal Global Change Biology, which showed that animal reproduction had shifted forward by 11 days between 1976 and 2005.
The new study, published in the Proceedings of the Royal Society B, used almost 400,000 records of annual first flowering dates for more than 400 species of plant such as hawthorn at sites across the UK.
Records stretching back to 1753 were used to create a 250-year index of the first flowering dates of the 405 species to show the impact of climate change.
The index showed a close link with the mean Central England Temperature – a record of average temperatures across the middle of England dating back to 1659 – for February to April, with each 1C rise correlating to first flowering dates occurring five days earlier.
Amassing the data has only been possible thanks to information received from members of the public.
The report was released by the UK Phenology Network, which is now run as the Nature's Calendar project by the Woodland Trust and the Centre for Ecology and Hydrology.
Richard Smithers, senior conservation adviser for the Woodland Trust, said the index helped scientists to see what was happening to the natural world as a whole – and acted as the canary in the coalmine.
"We used the plant data set because it's the best set. You could expand it across all species and all countries to come up with a global index," he said.
The most comprehensive records are from recent years, with the Nature's Calendar project dating back to 1998.
There are now 40,000 people across the UK registered as recorders and there were more than 93,000 submitted records in 2005 when the project was promoted on the BBC's Springwatch and Autumnwatch programmes.
But Smithers said there were also robust records dating from 1875-1947 as part of a project run by the Royal Meteorological Society.
And from the 18th century, naturalist Robert Marsham began recording a series of indicators of spring including the flowering of snowdrops and wood anemones, with his descendants carrying on the work up to the 1950s.
While spring this year is several weeks late because of the cold winter, Smithers said there was no doubt that long term changes could be seen in Britain's temperatures.
He warned that the response by plants could have negative impacts across the natural world.
"Plants are at the bottom of the food chain and we know from other work using Nature's Calendar that the higher up the food chain you go, the less responsive our animals are ...
"It could lead to a breakdown in the food chain with the result that things at the top of the chain will struggle and will need to move."
He called for more joined-up landscape, including more woodland cover to provide a number of benefits for humans such as air quality and flood defence – as well as helping wildlife to move.