If you went to Shaw Nature Reserve looking for black-eyed Susans in bloom in October 1950, you’d be out of luck looking for these late-summer yellow flowers. Now, you may spot these Missouri-natives blooming at the Nature Reserve as late as Halloween.
Changes in flowering times are a key plant response to climate change. Recent research from the Missouri Botanical Garden found Missouri native plant species are, on average, flowering 11.5 days longer.
Enjoying summer blooms well into the fall may seem like a bright spot among disastrous impacts of climate change, but scientists warn the small changes could have a big impact on local ecosystems.
Understanding this key plant response to climate change, and its effect on the ecosystem, is the only way to ensure their survival, said Garden Scientist Matt Austin, lead author of the study.
“My interest in studying the impact of climate change on flowering time is rooted in a deep love of plants and a desire to conserve them into future generations. By studying how climate change affects flowering, we gain information that is vital to protecting these species in a changing world.”
Matt Austin, Curator of Biodiversity Data at the Missouri Botanical Garden
Why does climate change affect flowering time?
Flowers bloom at the time that’s best for their reproduction and survival. Usually, that’s when their pollinators are most active and weather conditions are good for growth. Some plants can sense the time of year based on daylength, but most take clues from the weather. Spring-blooming species start flowering once temperatures warm to a certain threshold after winter. If rising temperatures cause warm weather earlier in spring, it will trigger earlier flowering.
what species did the study look at?
The study looked at 68 species native to North America, and specifically Missouri.
Some familiar species include the eastern redbud, butterfly milkweed, prairie purple coneflower, and late purple aster.
How is climate Change Affecting these native species?
On average, the study found these species flowered 11.5 days longer. But the exact effects varied among species.
Some saw no change at all. Others bloomed for the same amount of time, but earlier or later in the year. The flowering dogwood, Cornus florida, cream violet, Viola striata, and wild blue phlox, Phlox divaricata, all consistently flower a week earlier than they did in the early 19th century.
Did you know? The flowering dogwood is Missouri’s official state tree.
The most dramatic results were in the late-summer and fall blooming species like Black-eyed Susans, Rudbeckia hirta, brown-eyed Susans, Rudbeckia triloba, and Missouri coneflower, Rudbeckia missouriensis, all increased flowering time by more than a month.
“We believe that this lengthening of flowering time in the fall is due to rising temperatures causing cold winter temperatures to arrive later, which extends the period of the fall growing season,” Austin explained.
Aren’t More flowers a good thing?
Not necessarily.
The study found that 94% of species studied are experiencing greater flowering overlap at the community level. This means more flowers are competing for the same pollinators.
“Some species might become favored by pollinators at the expense of others, which would create a ‘winner-loser’ scenario, where some plant species do well at the expense of others,” Austin said.
Greater flowering overlap might also result in pollinators transferring pollen between different plant species. In some species, this will mean plants won’t reproduce.
Species blooming earlier, like the dogwood, may flower before their pollinators are active. Earlier bloom times also put spring plants at risk from getting hit by the last frost. This kills the flowers and limits the plant’s ability to reproduce that year.
How were the species chosen for the study?
All of the species Austin studied grow at Shaw Nature Reserve in Gray Summit, which the Garden purchased in 1925 as a refuge for its plant collection suffering from smog.
In the early 20th century, former Missouri Botanical Garden Director Edgar Anderson also observed, and recorded, bloom times of all of the species in the study during his weekly nature walks at the Reserve.
“While Anderson did not know this at the time, his observations would become an invaluable source of historic flowering information that we can compare modern flowering times to today,” Austin said.
“This legacy of research at Shaw makes it uniquely suited for studying how entire communities of plants have changed across the past century. It is thanks to the Garden’s preservation of Shaw across these many decades that it can now be used for rigorous botanical research, which can inform global plant conservation.”
Matt Austin, Curator of Biodiversity Data at the Missouri Botanical Garden
The Role of Herbaria in Climate change research
The Garden’s Herbarium also played a key role in the research. The Garden has one of the largest in the world with 8 million specimens dating back to the 17th century.
Given its location in St. Louis, Missouri plants are well represented with around 250,000 specimens in the Garden’s Herbarium. Of those, about 7,000 specimens collected in Franklin County where Shaw Nature Reserve is located, dating back to at least 1850. This allowed Austin and his colleagues to compare current bloom times with historic records of bloom times.
“This research highlights one of the most valuable contributions of herbaria: they are our main record of the history of plants on Earth. In any study of ecological or environmental change, we need a baseline to measure our current observations against. In relatively rare cases, like the phenology data from Shaw Nature Reserve, we have trustworthy written records that can tell us what the world was like decades or centuries ago. But in the vast majority of cases, these historic data come from specimens, carefully preserved and curated in the world’s herbaria, and increasingly made available digitally for rapid access by scientists around the world.”
Jordan Teisher, Herbarium Director at the Missouri Botanical Garden
The Garden recently announced it will digitize all its Herbarium specimens through the Revolutionizing Species Identification project.
Scientists around the world will be able to easily access the specimens for similar similar climate change research.
What’s next?
Now that Austin and his colleagues know climate change is affecting flowering times, they want to know just what that means for the plants.
“We know that Shaw’s plant community has shown drastic changes to flowering time, but what are the ramifications of this change?” Austin said.
He and his colleagues are also looking how this plant community has changed over time. For example, he is using Herbarium specimens to study how increased levels of carbon dioxide have affected stomata on plants from Shaw.
Stomata are plant “nostrils.” They facilitate the intake of carbon dioxide for photosynthesis and the release of oxygen and water.
Long-term, Austin hopes to continue observing flowering times of the same 68 species at Shaw Nature Reserve.
“Repeated sampling into the future would allow us to see whether the trends that we think will be present 10, 20, 30 years from now actually play out as expected,” he said.
Catherine Martin
Senior Public Information Officer
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