Scientists have underestimated plants’ response to warming, report says

As Earth warms, and spring comes earlier each year, plants will respond faster than scientists had expected, according to a new report.

Plants are leafing out and flowering sooner each year than what was predicted in controlled environmental warming experiments, according to a report published online in the journal Nature on May 2, 2012. The report indicates that scientists have been dramatically underestimating how plants will respond to global warming.

Researchers with the Boston-Area Climate Experiment are using techniques in their plant-warming experiments designed to better reflect natural daily and seasonal temperature cycles. This experiment is too new to have been in included in this study, but its design addresses some of the concerns raised by the study. (Credit: Jeff Dukes, Purdue University)

In the controlled experiments, researchers have manipulated the temperatures surrounding small plots of plants to gauge how specific plants will react to higher temperatures as Earth continues to warm. The plant responses are then incorporated into models that predict future ecosystem changes as temperatures rise over this century.

But when a group of scientists compared these results to a massive new archive of historical observations, they found that the warming experiments are dramatically underestimating how plants respond to climate change.

Elizabeth Wolkovich led the team of scientists behind the new research. She said:

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 warming experiments. The long-term records show that phenology is changing much faster than estimated based on the results of the warming experiments. This suggests we need to reassess how we design and use results from these experiments.

The researchers used an archive including data from 1,558 species of wild plants on four continents. The historical records showed that leafing and flowering will advance, on average, five to six days per degree Celsius. These data show that estimates based on data from warming experiments are underpredicting advances in flowering by eight and a half times and advances in leafing by four times. The authors expect the data archive to be an important benchmark in future phenology studies.

Cherry blossoms in Washington, DC have bloomed earlier in recent decades. March 2012 featured an exceptionally early bloom. (Credit: Elizabeth Wolkovich, Biodiversity Research Centre, University of British Columbia-Vancouver)

The study of phenology, the timing of annual plant events such as the first flowering and leafing out of spring, provides one of the most consistent and visible responses to climate change. Long-term historical records, some stretching back decades and even centuries, show many species are now flowering and leafing out earlier, in step with rising temperatures. Because these records aren’t available everywhere and predicted future warming is often outside the range of historical records, ecologists often use controlled experiments that create warmer conditions in small plots to estimate how different species will respond to expected temperature increases.

The timing of plants’ flowering and leafing out in spring is not only a basic, natural indicator of the state of the climate. Predicting plant responses to climate change has important consequences for human water supply, pollination of crops and overall ecosystem health.

Bottom line: According to a report published online in the journal Nature on May 2, 2012, plants are leafing out and flowering sooner each year than what was predicted in controlled environmental warming experiments.

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