The state tree of Missouri, the dogwood, bloomed especially early this year. The cupped white or red flowers started to pop out at the end of March, about two weeks earlier than the trees bloomed in the 1940s.
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Climate change is behind the early blooms in St. Louis, according to new research from local scientists. Warming temperatures are pushing bloom times in new directions for dogwoods and other plants that are native to the region, which could cause problems for their reproduction and other organisms that rely on them.
“If people are feeling like things are happening a little bit earlier than normal this year, they are not wrong,” said Nicole Miller-Struttman, an associate professor at Webster University who worked on the study.
To understand the effect of climate change on bloom times, scientists relied on two sources of data. One is a century of pressed dogwood clippings in the Missouri Botanical Garden’s herbarium, which is one of the largest in the world. Matthew Austin, the curator of biodiversity data at the Missouri Botanical Garden, worked on the study into how Missouri’s native plants respond to climate change.
“In ecology, it is very rare to have field data from long enough periods of time to be able to study the effects of climate change,” Austin said. “So a great alternative source of long-term data are herbarium records.”
The other source of data came from two time periods of nature walks in Shaw Nature Preserve, taken decades apart. In the late 1930s and early 1940s, Edgar Anderson, a former director of the Missouri Botanical Garden, conducted walking surveys, recording blooms and other data about the native plants there. About 70 years later, Miller-Struttman retraced Anderson’s steps.
“It was obvious relatively quickly that we were seeing things flowering a bit earlier and particularly flowering longer and later,” Miller-Struttman said.
When you put the real-world walking data and archived specimens from the herbarium next to weather records that are showing warming on average over time, you start to see the effect, Austin said.
“We have good evidence that this is related to climate change, because not only are we seeing a shift in flowering across the years, but we see a shift in flowering related to temperature data,” Austin said.
Altogether, the scientists observed many changes. Dogwood has had a pronounced response, Austin said, but that is also true for other native species. Flowers are coming out at least a week earlier on average for wild blue phlox, Dutchman’s breeches and the striped cream violet.
The celandine poppy has had one of the most dramatic changes — its bloom time has shifted by about two months. The bright yellow flowers are both appearing earlier and sticking around for much longer.
The effect of these changes is still a question for the scientists, but they have some concerns about what this could mean. Dogwoods fill an important niche in the ecosystem for the bees and flies that pollinate them, Austin said, so he worries this altered bloom time could throw off that timing.
Miller-Struttman studies how plants and pollinators interact and said this isn’t necessarily a bad thing, but her worry is that climate change is also affecting other elements of the ecosystem in different ways.
“For us, we think, ‘Oh, more things blooming at once, that's really beautiful, that's awesome,’ and it is in that way,” Miller-Struttman said. “But for the plants, that means more competition for the pollinators. So there's potential for these shifts in the timing to influence their relationship with pollinators and therefore their reproductive success or how many seeds they actually produce.”
Austin and Miller-Struttman hope to next learn more about climate change’s effect on plant reproduction.
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