By Rebecca Morelle
BBC News science reporter
The UK's plant species have experienced dramatic changes over the past 18 years in the conditions under which they grow, according to a new report.
The report details the trends in the UK's flora
Climate change, agricultural practices and human-made habitats have produced challenging environments for Britain's flora, the study shows.
Some species (18%) are thriving under the new conditions; others (16%) are in decline; most (66%) remain unaffected.
The Lottery-funded report is called Making it Count for People and Plants.
It is a joint initiative by the Botanical Society of the British Isles (BSBI) and conservation charity Plantlife.
The project, set up in 2002 and funded by the Heritage Lottery Fund, aims to identify the state of British flora and encourage more people to get involved in botany and plant conservation. It involved over 5,550 participants.
The project incorporated four strands, including surveys of single and common species and a rare plant register.
The most striking results came out of the BSBI Local Change Survey - a study that compared today's British plants to the flora of 18 years ago.
Between 2003-2004, over 750 botanists set about recording plants found in 811 2km-by-2km plots across Britain, collecting about 200,000 records. They were then able to compare their findings with a near identical study that had been carried out in 1987-1988.
The results provided a unique dataset, giving a comprehensive insight into changing flora in rural and urban habitats.
Overall, the survey found that 66% of species remained unchanged, 18% had increased in number and 16% had decreased.
The data revealed that many species had been affected by the increasing temperatures within the UK over the past 18 years. Some plants were shown to have benefited from the warmer environment, including species of orchids and ferns.
The deep pink pyramidal orchid (Anacamptis pyramidalis) and the bee orchid (Orphrys apifera), usually found in the south of England, have almost doubled in number, and have spread north and west through England.
"Warm summers have opened up gaps in the vegetation because some things die off, and these orchids fill in the gaps," explained Michael Braithwaite, of BSBI, who is an author of the report.
It was not all good news for orchids, he said. One of the northern orchids, the lesser butterfly orchid (Platanthera bifolia), has been doing badly, possibly due to climate changes.
"However, we found it much more difficult to show a decline in the northern species, mainly because these plants tend to be very long-lived," explained Mr Braithwaite.
Eutrophication - the unnatural enrichment of soil from agricultural run-offs - has also caused changes to flora, mainly affecting wetlands, chalk and limestone grassland and heathland.
The increase of nutrients causes nitrogen-loving plants to thrive, but these can drive out other species.
"If you apply fertiliser to a field that has a mixture of plants, the tougher ones take over - and they tend to be mainly the grasses," said Mr Braithaite.
"For example, the rye grass does very well with fertiliser, making a lush crop for the livestock, but they push out some of the other species."
Katherine Stewart, from Plantlife, said the findings from their Common Plants Survey - an annual survey of the UK's native flora which forms one strand of the report - echoed these results.
"We've seen plants that like low nutrient levels, such as birds-foot trefoil (Lotus corniculatus), decline; whereas plants that really like nutrients, such as nettles, have shown an increase."
Changes to agricultural practices seem to be creating other changes to the UK flora.
Since the intensification of agriculture after the World War II, "arable weeds" have been in sharp decline; but the results of the survey indicate that this decline might have been halted.
"This was a big surprise," said Dr Chris Preston, a botanist from the Centre for Ecology and Hydrology, Monks Wood, who worked on the BSBI study. "We didn't expect to see that at all."
He said the change may be down to environmental schemes, such as set-aside fields and uncultivated heathland, which had been introduced since the older survey, allowing arable weeds such as the long-headed poppy (Papava dubium) to boost their numbers.
However, Dr Preston pointed out that this was a modest increase from an already low baseline of plants.
Human interventions are also causing flora changes, including the introduction of alien species and changes to habitat.
"Man has produced some habitats that are rather radically different to anything found in nature, but it doesn't mean that nothing grows in them," explained Mr Braithwaite.
"You've only got to look in your own garden or along a roadside, and there is always something that comes up.
"The change in transport routes has also caused an alteration in plant species, such as the prickly lettuce (Lactuca serriola. It has been growing along the roadside in no uncertain way."
Michael Braithwaite said the report also produced some surprising findings.
"Some of the native species that we found were doing well when we thought they were doing badly.
"There is a little chap called sand spurrey (Spergularia rubra) that has been rattling along forestry track. We knew it in little sand grasslands which were getting fewer and fewer and we thought it was on the way out. But, hey presto, it's found itself a new habitat and is doing fantastically."
Overall, said Mr Braithwaite, it was important to remember that the report showed there were as many gains as there were losses.
"This isn't something new - our countryside has been changing for hundreds of years - but we've seldom had the information in this detail. There is so much to learn about the British countryside; every time we look closer we discover more and more."