Science Matters – flowers provide the evidence

The average flowering time in the UK has advanced by 26 days since 1986. Photo: The Woodland Trust

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I expect that many readers of this column are keen gardeners, and if so will probably have noticed that spring flowers seem to be flowering earlier year on year.

I certainly have, and now an international group of scientists have proved this observation to be statistically valid.

To investigate plant phenology – that is, the annual sequence of plant developmental stages – the scientists used records from a citizens’ science project run by the Woodland Trust called Nature’s Calendar, in which the UK public can record first flowering dates (as well as many other harbingers of spring such as sighting of migratory birds and emerging insects).

This vast database is described as ‘the longest written biological record of its kind with almost three million records spanning 300 years’.

Using this gold mine of information, the scientists accessed 419,354 records of first flowering dates (FFD) from 406 UK plant species between the years 1753 and 2019. First they compared all FFD before 1986 with all those after that date.

The results show that UK-wide the average flowering time has advanced by 26 days since 1986, a finding that correlates with the rise in average temperatures in the meteorological records over the same time period*.

The largest shift in FFD was 32 days, recorded in herbs (defined as non-woody, seed-bearing plants that die down to ground-level after flowering), while a massive 41 day difference was recorded between wind-pollinated and the earlier flowering insect-pollinated herb species.

Geographical differences were also noted, with mean flowering time being six days earlier in the south than the north, five days earlier in urban than rural areas and one day earlier at lower than higher elevations.

To date winter warming has exceeded temperature rises in other months, and if it continues it will have implications for the alignment of biological requirements of ecosystem components.

For example, early bud breaking and flowering increases the risk of frost damage and may also reduce the chances of pollination, both of which will decrease seed production.

The scientists conclude that if this trend continues then ‘the functioning and productivity of biological, ecological and agricultural systems will be at an unprecedented risk’.

* Buntgen U et al. Proc R Soc B 289:20212456.