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They are dry and brittle now, the showy orchids that Victorian-era flower-lovers plucked from English meadows and carefully pressed onto vellum sheets. But the faded blooms confirm that spring flowers are blooming earlier in the United Kingdom (UK) due to a warming climate, according to a new study.

Field records have long suggested climate change is driving changes in plant “phenology” – the timing of flowering and the budding of leaves. But there are few records that reach far into the past, making it difficult to detect trends. To get a better historical perspective, a team of ecologists from the UK’s Royal Botanic Gardens and the universities of East Anglia, Kent, and Sussex looked to old collections of pressed plants kept by major botanic gardens and museums.

In particular, the team reports in the current Journal of Ecology, they examined 77 specimens of the early spider orchid (Ophrys sphegodes) collected around Britain between 1848 and 1958. Each had details about when and where it was picked, which researchers were able to match with archived weather data. Then, they compared the pressed-flower data with field observations of the same orchid made between from 1975 to 2006 in the Castle Hill National Nature Reserve in East Sussex.

Then and now, spider orchids bloomed when spring temperatures reached a certain threshold, the team reports. And as a result of a warming climate, the orchid has been flowering 6 days earlier for every 1 degree Celsius in mean spring temperature.

The unusual study suggests that pressed plant collections – some of which include specimens collected centuries ago – “may provide valuable additional information for climate-change studies,” says the study’s lead author, PhD student Karen Robbirt of the University of East Anglia. And such “historical ecology” may give scientists “some confidence in our ability to predict the effects of further warming on flowering times.” David Malakoff

Source: Karen M. Robbirt, Anthony J. Davy, Michael J. Hutchings and David L. Roberts (2010). Validation of biological collections as a source of phenological data for use in climate change studies: a case study with the orchid Ophrys sphegodes Journal of Ecology : 10.1111/j.1365-2745.2010.01727.x

Image © Jody Elliott