Despite global warming accelerating since the 1970s, when early spider orchids in the UK flower still varies with temperature in exactly the same way that it has for the past 150 years. By studying preserved plant specimens known as herbaria, researchers from the Universities of East Anglia, Sussex and Kent have found that orchids consistently flower 6 days earlier for every 1ºC rise in average spring temperature. Measurements of how species react to climate changes are rare, and so this first clear demonstration that herbaria can fill these gaps creates a powerful new scientific weapon.
“It is estimated that some 2.5 billion specimens of flora and fauna are held in biological collections worldwide,” the University of East Anglia (UEA)’s Anthony Davy and colleagues wrote in the Journal of Ecology this week. “With appropriate validation, the exploitation of this resource will have increasing relevance and value as we seek to understand and predict the consequences of continuing climate change.”
The British scientists examined 77 herbaria of the early spider orchid collected between 1848 and 1958 and held at the Royal Botanic Gardens, Kew and the Natural History Museum in London. Each herbarium contains details of when and where the flower was picked, and preserves it in the state it was in at that time. This allows the researchers to examine how average spring temperatures affected the orchids’ flowering.
Field observations of the same orchid species in the Castle Hill National Nature Reserve, East Sussex, from 1975 to 2006 published in March showed that peak flowering occurred half a day earlier each year on average. Comparing these data to the herbaria, Davy’s team found that the response of peak flowering time to average spring temperature was identical.
The study of the how the timing of natural climate-driven events like flowering changes, known as phenology, is often hampered by of a lack of measurements, Davy explained. “For most species, data collected specifically for the study of climate-induced phenological change are not available, or are difficult to find, reflecting the scarcity of long-term monitoring schemes,” he said. Not only do herbaria fill this gap, but when used to foretell the effects of later climate warming the scientists found “the overall predictive power was extremely good”.
“Recent climate change has undoubtedly affected the timing of development and seasonal events in many groups of organisms,” Davy continued. “Understanding the effects of recent climate change is a vital step towards predicting the consequences of future change. But only by [studying] the responses of individual species will we be able to predict the potentially disruptive effects of accelerating climate change on species interactions,” he says.