If plants can’t flower earlier to adapt to global warming they’re probably being driven away from where they used to grow, towards cooler places. That’s what new findings on how these responses are linked from Tatsuya Amano at the University of Cambridge and his teammates suggest. “We believe that the link we’ve revealed will help us understand the complex implications of climate change on biodiversity,” Tatsuya told me. “Many studies have relied on models that only consider species’ spatial responses for projecting the impact of climate change on species. We might be able to generate more realistic projections.”
You could think of regular natural events, such as flowering in plants, as being triggered by an alarm clock – another type of dandelion clock, if you like. The study of when those alarms go off is known as phenology. In 2009, Tim Sparks from Coventry University visited Tatsuya, Bill Sutherland and others in Cambridge to give a talk on changes in when these events were happening. He was helped by notes on plant life many people in the UK had jotted down in their spare time, but that data’s inevitable patchiness caused him problems.
Bill and Tatsuya were working on mathematical models that helped fix similar problems in bird count data, and so they offered to help Tim with his work. They were also joined by Richard Smithers, then in charge of the Nature’s Calendar archive run by the UK’s Woodland Trust. He helped them realise the power of this publicly-accessible record of over 250 years’ worth of data on 405 UK species, nearly 400,000 records in all. Using that information, in 2010 the team showed that UK flowers are now blooming earlier in the year than in any 25-year period since 1760.
Time- and space-travellers
Climate change is also driving plants into new homes, mostly towards cooler conditions nearer the poles or uphill. Both timing and growth site changes happen because each species is used to living in niches that provide certain conditions – particular temperature, rainfall and sunlight levels, for example. But some species have not moved, and Tatsuya and his colleagues wondered if their dandelion alarm clock was being reset instead. “What causes this varied response among species is still under debate,” he said. “It seemed logical that these two responses might be linked, that is, plants that do not move north may instead be tracking warming temperatures by advancing their phenological events.”
Seeing if this link exists needs lots of data, but Tatsuya’s team could build on their previous work. They looked around two-thirds of the species from that study, those with enough of the right type of data to allow a reliable comparison against temperature. With that information they could see if plants were resetting their clocks to stay in their niche without moving to new habitats in the period from 1930-2009. They found 132 of the 293 species they studied in this way were flowering significantly earlier, and three significantly later. 267 species overall felt no significant increase in temperature at the time when they first flowered.
To look at where the plants are growing, Tatsuya and his co-workers turned to another website, the UK’s National Biodiversity Network Gateway, covering over 6,500 species and more than 375 years. From that they took average map co-ordinates for where the species were found, and average temperature for the month in which they flower first each year. Using that information the scientists could study changes in the niches where plants could grow successfully by comparing two periods, 1930-1960 and 1987-1999. 225 of the 284 species they looked at in this part of their study had moved northwards, 59 southwards, meaning only 17 experienced a temperature rise above 0.5°C.
Evidence of climate change in our backyard
Bringing the two analyses together showed that species that had failed to reset their clocks were found further north on average. That lets them stay in their niche, while without either a change in timing or place they would have been hotter during flowering time. In a paper published in Proceedings of the Royal Society B last week, Tatsuya’s team say the apparent move is probably because in the south untimeshifted plants died out. There was also a difference between annual plants, which only live a single growing season, and perennials that come back year after year.
“The link between phenological changes and range shifts was stronger in annual species,” Tatsuya explained. “38 of the perennial species studied did not track the climate either by flowering earlier or by shifting north. These species merit attention, as they could be either highly vulnerable to climate change due to their inability to track changing temperatures, or fairly resistant to changes in climatic conditions and need not respond.”
Tatsuya now wants to look to see if they can see similar links in other forms of life, and develop models that include both forms of response. He also stressed that these findings show how valuable data collected by people like you and me can be in helping understand climate change. “Citizen science makes studies like ours possible,” the scientist pointed out. “I would like to thank the countless people who have made these data available.”
Tatsuya Amano, Robert P. Freckleton, Simon A. Queenborough, Simon W. Doxford, Richard J. Smithers, Tim H. Sparks and William J. Sutherland (2014). Links between plant species’ spatial and temporal responses to a warming climate Proceedings of the Royal Society B DOI: 10.1098/rspb.2013.3017