Experiments on how plants respond to climate change may have lulled us into a false sense of security by dramatically underestimating the effects.
An analysis of 50 plant studies on four continents has found that shifts in the timing of flowering and leafing in plants due to global warming appear to be much greater than estimated by warming experiments.
"This suggests that predicted ecosystem changes - including continuing advances in the start of spring across much of the globe - may be far greater than current estimates based on data from experiments," says ecologist Elizabeth Wolkovich, now of the University of British Columbia.
Long-term historical records show that many plant species are coming into leaf and flowering earlier, as temperatures have warmed over recent decades. The right data's not always available, though, which is why ecologists often experiment by warming small field plots to examine plant responses.
But Wolkovich and her colleagues found that experiments underpredicted plant phenological responses to temperature by at least four time, whencompared to long-term records. These consistently show that leafing and flowering advance, on average, by five to six days per degree Celsius - a finding that's strikingly consistent across species and datasets.
There could be a number of reasons, including specific aspects of the experimental design. But the team's analyses indicate that, within the range of temperature increases considered, the problem could be how researchers manipulate temperatures and how accurately they measure them.
"Researchers use a variety of methods to increase temperatures in the field - including heating cables in the soil, small greenhouse-like structures and heating above plants," says Wolkovich.
"We found that plant sensitivities to temperature vary with the design of the experiment, with above plant warming producing consistent advances in flowering."
The difference in responses from experiments andlong-term records has important consequences for predictions of species diversity, ecosystem services and global models of future change.
"Long-term records appear to be converging on a consistent average response to climate change, but future plant and ecosystem responses to warming may be much higher than previously estimated from experimental data," says Elsa Cleland of UC San Diego.