The researchers fear that the diversity found in woodlands could be lost forever
British woodlands are less biologically distinctive than they were 70 years ago, says a team of UK researchers.
The use of fertilisers in farming had increased soil fertility, while tree canopies had grown thicker and cut light levels, they explained.
As a result, the woodlands were becoming home to the same species, resulting in the unique characteristics of individual sites being lost.
The findings appear online in the Proceedings of the Royal Society B.
The research was carried out by scientists from Bournemouth University, Natural England and the Centre for Ecology and Hydrology (CEH).
"This study shows that increased pollution and poor countryside management have led to increasing homogenisation of biodiversity in British woodlands," said co-author Professor James Bullock, an ecologist from CEH.
"These two issues must be addressed in future if we wish to restore the diverse woodland communities of the past."
The researchers initially looked at a dataset of plant records from more than 7,000 sites in Dorset collected in the 1930s.
The lack of woodland management, such as coppicing, has cut light levels
They then revisited 86 of the woodlands that were used in the original survey, and recorded the plants that were found at the locations.
Comparing the two sets of data, the team found that while the average number of plant species found in the woodlands had remained the same, there was a "significant" reduction in the diversity of species.
"Biotic homogenisation has major implications for biodiversity conservation," the team observed.
"It is related to the loss of unique species combinations, leaving an impoverished version of the past variety of nature."
They found that the soil was now more fertile than in the 1930s, which they said was a side-effect of the use of fertilisers.
They added that the composition of plant species suggested that there was less light reaching the woodlands' floor.
One reason for this was thicker canopies, probably a result of the decline in traditional management techniques, such as coppicing.
Lead author Sally Keith, from Bournemouth University, concluded: "The results show that we must monitor biodiversity at the landscape scale, as well as gaining a better understanding of processes affecting our native flora if we are to conserve and restore the character of the traditional British woodland."