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Experiments Underestimate Climate Change Impacts to Plants
See caption:

A Gillette's checkerspot butterfly visiting sneezeweed. Credit: A. Miller-Rushing

As the climate has warmed, many plants are starting to grow leaves and bloom flowers earlier. A new study published in the journal, Nature, suggests that most field experiments may underestimate the degree to which the timing of leafing and flowering changes with global warming.

Understanding how plants are responding to climate change will help develop more accurate indicators of spring, forecast the onset of allergy season or the chances of western wildfires, manage wildlife and invasive plants, and help inform habitat restoration plans.

In this new study, scientists evaluated the sensitivity of plants to changes in temperature using two sources: experimental plots versus historical observations from natural sites.

The experiments analyzed in this study were conducted by artificially inducing warming in small study plots, and then measuring plant responses. The historical observations entailed long-term monitoring of multiple species at natural ecological research sites without any manipulation. The date of leafing and flowering was synthesized for dozens of warming experiments and monitoring sites across the Northern Hemisphere.

Scientists conclude that compared to warming experiments, historical monitoring shows temperature sensitivity to be four times greater for leafing and over eight times faster for flowering.

An woman seated in a field of wildflowers records observations

Recording how climatic variations and trends impact seasonal events in plants. Credit: A. Miller-Rushing

On average, the warming experiments predicted that every degree rise in Celsius would advance plants’ flowering and leafing from half a day to 1.6 days, while historical observations indicate a temperature sensitivity of about 5 to 6 days per degree Celsius. The finding was strikingly consistent across species and datasets. Conclusions from this study are based on analysis of more than 1600 plant species on four continents.

The study of how climatic variations and trends impact seasonal events in plants and animals is termed “phenology.” This includes when cherry trees or lilacs blossom, when robins build their nests, when salmon swim upstream to spawn, or when leaves turn colors in the fall.

The study was conducted by an interdisciplinary team led by Elizabeth Wolkovich, with the University of British Columbia, and Ben Cook, with NASA-Goddard. The study was funded by the National Science Foundation, the State of California and the University of California, Santa Barbara. The U.S. Geological Survey (USGS) and the USA-National Phenology Network (USA-NPN) also provided support and assisted with assembling and analyzing historical phenological observations and climate data.

Future Tracks: Experiments and Observations

A woman examines flowers in a field, recording her observations

Observing changes in the seasonality of plants in Concord, Massachussets. Credit: A. Miller-Rushing

The authors of the Nature paper recognize the value of both experiments and monitoring. They call for standardization of measurements and protocols as well as improvements in experimental design, and continuation and expansion of long-term monitoring efforts like the USA-NPN.

The USA-NPN brings together citizen scientists, government agencies, non-profit groups, educators and students of all ages to monitor the impacts of climate change on plants and animals in the United States. The USA-NPN was established by the USGS in collaboration with the National Science Foundation.

“This study underscores the reasons for recent establishment of a USA-NPN to help track, understand, and hopefully forecast different species responses to climate variability and change across the U.S.,” said USGS scientist Julio Betancourt, who is a co-author of this new report.

You Can Help! Track the Pulse of our Planet

We need your help to track the pulse of our planet. Through the USA-NPN’s Nature’s Notebook, citizens across the nation are providing data on plants and animals.

People like you — gardeners, farmers, birders, hikers, anglers, joggers, or all-around nature enthusiasts — are already recording the recurring events they see in the lives of the plants and animals around them. This includes when cherry trees or lilacs blossom, when robins build their nests, when salmon swim upstream to spawn, or when leaves turn colors in the fall.

Become involved and sign up through the USA-NPN website, or contact the USA-NPN Executive Director Jake Weltzin at

See caption:

Mining bee on great false leopardbane in Concord, Massachusetts. Credit: A. Miller-Rushing

More Information

Read a University of California, San Diego, press release, as well as a NASA feature, on this new article.

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