Peter Dowdall: How climate change is shifting when flowers bloom

As temperatures warm plants, including wildflowers, may respond by adjusting the timing of life-cycle events such as flowering

Plants, insects, and wildflowers play a vital role in maintaining biodiversity. File pictures

Horticulture  and botany know nothing about politics and thankfully, instead of having splintered into several societies, the Botanical Society of Britain and Ireland (BSBI) remains the biggest and most active organisation devoted to the study of botany in Britain, Ireland, the Channel Isles and the Isle of Man.

This is a society for anyone and everyone interested in the flora of Britain and Ireland. The main role of the society is the study, understanding and enjoyment of wild plants in Britain and Ireland. It does this in many ways, the BSBI supports an education and training grants programme, scientific research and outreach programmes along with publishing newsletters and recording flora distribution and populations in national atlases and county floras.

Native wildflowers play a vital role in maintaining biodiversity. They provide habitats and food sources for a wide variety of insects, birds, and other wildlife. By supporting diverse ecosystems, they contribute to the overall health and stability of natural environments and we humans need to monitor them, to see what is growing, where they are growing, how population numbers are changing and to note any change in their habits.

The 2024 BSBI New Year Plant Hunt ran from Saturday, December 30, to Tuesday, January 2, 2024, and more than 3,000 people, a record number, took part in the hunt after the hottest summer on record was followed by an unusually wet December.

Among the findings collated from the 21,096 records of plants in flower which were submitted was that 629 plant species were in bloom, a 30% increase compared to last year and the third highest total in the history of the hunt and around half the species in bloom were flowering later than expected with around a quarter flowering earlier than expected.

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This shift in blooming times is often attributed to climate change. As temperatures warm, many plants, including wildflowers, may respond by adjusting their phenology, which is the timing of life-cycle events such as flowering.

Warmer temperatures can trigger plants to flower earlier in the year. This can have a range of ecological implications. Over many thousands of years, plants and insects have developed and adapted together and this change in flowering time can potentially have a detrimental impact on both the plant and the insects with which it has symbiotic relationships.

Flowering earlier can impact the synchronization of flowering with the life cycles of pollinators and other species that depend on the plants. For instance, if a wildflower blooms before the emergence of its primary pollinator, it could affect the reproductive success and thus, future survival, of both the plant and the pollinator.

BSBI chief executive Julia Hanmer described the results of the New Year Plant Hunt as “inspirational”. “It was a joy to take part myself and also to hear about other people’s experiences on
social media, with so many people joining the hunt for the first time this year,” she says. “There was a fantastic sense of the botanical community coming together to learn about and contribute to our understanding of wild plants. Thank you to everyone who took part.”

Only 20% of the records submitted were of species we might reasonably expect to flower at New Year, or species which cannot easily be categorised as either “early” or “late”. These include typical “all year rounders” such as shepherd’s purse as well as “winter specialists” such as winter heliotrope.

Thirty-five per cent of species recorded were non-natives or “alien” species. This includes plants from warmer climates that have escaped from gardens or cultivation, become naturalised in the wild and were able to extend their flowering into the winter months.

Insects, such as the peacock butterfly pictured on wild basil, and plants have developed and adapted together to maintain biodiversity. 

As the analysis of the New Year Plant Hunt data shows, our plants are responding to changing weather patterns, with more flowers being recorded during the past decade as we experience autumns and winters with warmer temperatures and fewer frosts, according to BSBI head of science Kevin Walker.

“We cannot, however, prove conclusively that more species are flowering nowadays in mid-winter compared to in past years or what that will mean for the wildlife that relies upon them but we can see that weather patterns are changing and our plants, both native and non-native, are responding,” he adds.

Whilst various species are flowering earlier in different regions, the extent of this shift can vary depending on factors such as local climate trends, elevation, and habitat type.

It’s important to note that not all wildflower species are responding to climate change in the same way, and there can be variability among species and populations.

Monitoring changes in the timing of wildflower blooming, along with other phenological events, is an important aspect of understanding the ecological impacts of climate change and can provide valuable information for conservation and management efforts.