(NASA) - Plants are leafing out and flowering sooner each year than predicted by
results from controlled environmental warming experiments, according to
data from a major new archive of historical observations assembled with
the help of a NASA researcher.
Researchers use experiments that manipulate the temperature of the
environment surrounding small plots of plants to gauge how specific
plants will react to higher temperatures. The observed plant responses
can then be incorporated into models that predict future ecosystem
changes as temperatures around the globe continue
to rise. 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.
The results were published online in the journal Nature on May 2. In
addition to quantifying how a broad collection of plant species have
responded to date to rising temperatures, the study suggests that the
way warming experiments are conducted needs to be re-evaluated.
Cherry blossoms in Washington, DC have been blooming earlier in recent
decades, including a very early bloom this spring in March (pictured).
(Credit: Elizabeth Wolkovich, Biodiversity Research Centre, University of British Columbia-Vancouver)
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"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,"
said Elizabeth Wolkovich, who led the interdisciplinary team of
scientists behind the new research while she was a postdoctoral fellow
at the University of California, San Diego. "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."
Benjamin Cook, of NASA's Goddard Institute for Space Studies and
Columbia University, New York, worked with Wolkovich to create the
massive new archive of long-term, natural phenology observations to
gauge the accuracy of the phenological predictions based on these plant
warming experiments. The archive includes 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 -- a finding that was consistent across species and datasets.
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.
"These results are important because we rely heavily on warming
experiments to predict what will happen to ecosystems in the future,"
said Cook, who helped bring together a research team including support
from the National Center on Ecological Analysis and Synthesis to build
the archive of real-world observations. "With these long-term
observational records you may be able to pick up a shift in a plant
community over a few years that you wouldn't be able to observe in an
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
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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.
Wolkovich, Cook and colleagues suggest a number of potential reasons the
estimates based on experimental data have underpredicted the plant
response to higher temperatures. There could be additional effects of
climate change not mirrored in the controlled experiments, or from the
fact that the methods used to create warmth in the studies could be
creating counteracting effects such as drying out soils or reducing the
amount of sunlight reaching the plants.
"Continuing efforts to improve the design of warming experiments while
maintaining and extending long-term historical monitoring will be
critical to pinpointing the reasons for the differences, and will yield a
more accurate picture of future plant communities and ecosystems with
continuing climate change," Wolkovich said.