Cascading Climate Change Impacts on Missouri Flowers and Pollinators

    By Kathleen Berger, Executive Producer for Science and Technology

    Many people welcome early and cheerful blooms in the spring, but the reality of flowers blooming earlier in Missouri is less cheerful for scientists studying the impact of climate change on flowers and pollinators in the St. Louis area.

    “Markedly earlier flowering in a lot of species,” said Matthew Austin, PhD, an ecologist and biodiversity postdoctoral fellow with the Living Earth Collaborative at Washington University in St. Louis.

    Flowers that rely on bees and other pollinators to transport pollen between flowers of the same species — buzzing from violet to violet, for example — face uncertainties when spring and summer become front-loaded with flowers blooming earlier and flowering season lasting longer. Suddenly, the pollinators have a lot more flower options at the same time earlier in the season.

    Austin is on a mission at Shaw Nature Reserve in Gray Summit, Missouri, an extension of Missouri Botanical Garden, to discover the impact of a more competitive spring flowering season on plants native to the St. Louis area. His research started in the spring of 2021. 

    “The project that I’m working on is looking at the ecological and evolutionary implications on pollination systems as a result of a change in climate,” he explained. “We know that climate change has altered the time of year that plants flower in certain places, including the greater St. Louis area. We see that a warming climate is not only causing flowers to bloom earlier, but in many species, it’s also causing flowering to end later.”

    Austin said earlier blooms and a longer flowering season would be confusing to bees and other pollinators. Suddenly, there are a lot more flowering options at one time.

    “Flowers might have shifted earlier, while the time of year that bees are active has stayed the same.”

    And if bees are confused and things don’t happen the way they’re supposed to, the beauty and survival of certain species of flowers may suffer. To determine potential outcomes, Austin reviewed historical records of flowering times collected along a stretch of path at Shaw Nature Reserve dating back to the 1930s, to early 40s. According to the data, most of the species at Shaw Nature Reserve are flowering at a different time now than they used to about 80 years ago. To get more answers, Austin conducted a controlled pollination study.

    “To conduct my hand-pollination experiments, I’m doing the work that a bee would do. However, to be very careful and controlled in my experimentation, I have to make sure that other bees or other pollinators aren’t also pollinating the flowers that I’m working with,” he explained.

    With climate change and many different flowers in bloom at the same time, cross-pollination by confused busy bees, for example, is more likely.

    “The question that my hand-pollination experiments are testing is whether – if a flower receives pollen from a different species, it will be a reproductive dead end. Will that flower not reproduce at all, compared to if that same type of flower received pollen from a different flower of its own species.”

    Austin is trying to determine whether flowers that receive pollen from a different species will produce fewer seeds than flowers that receive pollen from their own species. Through close examination, Austin found that Bloodroot (Sanguinaria canadensis) flowers produce fewer seeds when they receive pollen from Spring Beauty (Claytonia virginica) flowers. Austin explained the preliminary evidence suggested that their flowering seasons overlap more now than they did a century ago. Both are now blooming at the same time in the spring. So in 2022, Austin’s research will try to determine if Bloodroot began to receive pollen from different species at higher rates during the increased duration of flowering seasons from climate change throughout the 20th century. 

    Austin’s research also sheds light on how there’s more than flowers to consider. 

    “The time of year that bees are out, they could be left without the flowers that they normally feed from. While research is ongoing on bee populations, if bees are not able to feed from flowers that they have historically in the past, if they’re not able to shift to feeding on a different species, you could see declines of their populations,” said Austin. “We’re similarly concerned about declines of other pollinators, such as butterflies, flies, moths. It’s hard to predict because ecosystems are incredibly complex and interconnected communities and you never know what the cascading effects of one change will have on other organisms.”