Early bloomers: The effect of a warming climate on flowering times

Jenna Zukswert
30 April 2015

Above: Cherry blossoms at the Kyoto Botanical Garden in Japan (Wikimedia Commons/Yoko Nekonomania)

Spring is an exciting time, when snow melts and flowers start to bloom. But have you ever noticed that flowers don’t bloom on exactly the same day every year? On average, many flowers are actually blooming earlier now than they used to. Why is this and how are scientists studying these changes? The explanation has a lot to do with rising temperatures, and citizen scientists like you can help researchers better understand climate change and its effects on plants.

Flowering time depends on the environment and climate. Flowers don’t use calendars to know when to bloom. Instead, plants mainly know what time of year it is by how long the days are or, more commonly, how long the nights last. But other environmental factors, especially temperature, also influence flowering times.

Did you know? Thanks to government records, scientists have been able to gather data on the flowering times of cherry trees in Kyoto, Japan, for the last 1,200 years!Because plants are so sensitive to temperature changes, increasing average annual temperatures—a symptom of climate change—are causing many flowers to bloom sooner than they have in the past. In Canada, for example, plants have been flowering an average of 9 days earlier for every 1°C increase in average annual temperature. Since the average annual temperature increased by 1.4°C between 1948 and 2009, plants today are flowering about 12 or 13 days earlier than they did in in the 1940s.

These changes mean that some interactions between flowers and animals that depend on timing, such as availability of nectar and pollen, may be disrupted. For example, bees might start their pollination activity after some plants have already flowered. As a result, crops might not get pollinated, bees might not be able to produce honey, and a variety of other species—including humans—might not have enough food.

To properly study how the climate has changed over time, scientists need to collect as much data as possible on when plants start to flower. Researchers cannot go back in time (yet!) to see when different flowers bloomed past, but they can rely on the next best thing: historical records.

For example, researchers can figure out when flowers bloomed in the past by looking at old plant specimens preserved in herbariums. Herbariums are special museums just for plants, consisting of rows of metal cabinets filled with dried specimens that have been mounted to pieces of paper. People have been collecting and preserving plants this way for hundreds of years. If the plant specimen was flowering when it was preserved, and the collector recorded the date, researchers can assume that the plant was flowering in nature at that time too. Scientists can also use historical photographs to estimate flowering time, as long as they know when the photograph was taken.

Did you know? NatureWatch Canada runs four different citizen science projects: PlantWatch, FrogWatch, IceWatch, and WormWatch. Learn about how you can get involved!Historical flowering times can be compared to present-day flowering times, but it can be difficult for a lone scientist or a small research group to collect all the data they need on their own. This is where you come in! There are currently several citizen science projects—projects that allow anyone to get involved in research by collecting or analyzing data—for sharing information on flowering time.

For instance, the study that determined that Canadian plants are bloom about nine days earlier for every 1 °C increase in annual temperature used observations made by Canadians through the PlantWatch program. The project is ongoing and all you need to participate is watch for blooming flowers and record where you are, what kind of plant it is, and when you saw it flower for the first time this year.

Scientists have already learned a lot about climate change and have begun to observe many of its consequences, such as earlier flowering times and possible changes in interactions between plants and animals. However, climate change is extremely complex and there is still a lot to discover. By recording when you see flowers start to bloom, and letting scientists know, you can contribute data and help researchers predict and understand other environmental changes that may result from climate change.

Learn more!

Citizen Science: linking the recent rapid advances of plant flowering in Canada with climate variability (2013)
A. Gonsamo, J. M. Chen & C. Wu, Scientific Reports 3

The history of public participation in ecological research (2012)

A. Miller-Rushing, R. Primack & R. Bonney, Frontiers in Ecology and the Environment 10

Discussions on the role of citizen science in climate and environmental research.

Temperature trends in Canada (2013)
Jeff Fritzsche, Statistics Canada

The impact of climate change on cherry trees and other species in Japan (2009)

R. B. Primack, H. Higuchi & A. J. Miller-Rushing, Biological Conservation 142
Link to abstract. Subscription required to view full text.

Photographs and herbarium specimens as tools to document phenological changes in response to global warming (2006)

A. J. Miller-Rushing, R. B. Primack, D. P. & S. Mukunda, American Journal of Botany 93

Articles discussing research realated to climate change and flowering times.

Jenna Zukswert

I am an MSc student in Forestry at the University of British Columbia, where I am studying leaf litter decomposition on the forest floor. Before moving to Vancouver, I lived in a small town in the state of Vermont, surrounded by forests. Forests are fascinating and important ecosystems, and I love learning about them.

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