Last week, I took a few minutes to observe a flowering display that has been sought by many each spring. The cherry trees in the Illinois Arboretum were in full bloom, the sun was shining, and there was quite a crowd of admirers.
The ritual of taking in the cherry trees is not unique to our arboretum and has been a longtime tradition around the globe, originating in Japanese culture as early as the eighth century. In the U.S., the most notable cherry blossom bloom is likely in our nation’s capital, where cherry trees line the Potomac waterfront, drawing over one million visitors a year. The original cherry trees in Washington, D.C., were a gift from Japan in 1912, which has perpetuated this ancient tradition in the U.S., gaining popularity every year.
The annual observation and appreciation of cherry blossoms is one way modern-day humans observe phenology, defined as the annual timing of natural processes such as cherry blooms or insect emergences. However, our species has been observing these natural occurrences for eons.
Long before ancient humans began the culture-based observation of cherry blossoms, knowledge of phenology was a key to survival. It was important to understand and predict when a particular fruit might ripen, or vital game populations may migrate.
While humans may intentionally coordinate with phenological events through learned behaviors, other species have long co-evolutionary histories that have resulted in uniquely timed occurrences. Many pollinators’ life cycles are timed with the appearance of flowers vital to their food supply. In turn, plant reproductive cycles are also dependent on the co-relationship to ensure pollination occurs and viable seeds are produced to perpetuate plant populations. Ecologically, there are many more of these examples, which all serve to illustrate the incredible connectedness in the natural world.
Today, researchers around the globe are continuing to monitor and study phenology, with changes in these annual events emerging as some of the most striking signs of our warming climate.
A 2023 research paper made the most of cherry blossom data over the ages, using 1,200 years of information to compare historic bloom timing to the timing in recent decades. Using the extensive dataset in Kyoto, Japan, and other sites around the globe, researchers found that cherry trees have been flowering earlier in the last several decades compared to the past thousand years. Specifically, in Washington, D.C., cherry trees are blooming nearly a week earlier each spring, on average.
Phenological events in the insect world are also experiencing changes with our warming climate. Life events such as spring emergence, migration timing and the transition to overwintering life stages are happening later in many populations.
Weather data here in the U.S. indicates the growing season is getting longer by about two weeks in most locations. Since many any insects produce multiple generations per year, a longer growing season can result in additional generations each year. While this may be good for hungry predators, it may be determinantal to crops affected by additional pest generations.
For millennia, insect and plant phenology have coincided in the natural world, but a growing body of research is assessing this synchrony and finding that climate change may be throwing things off. A 2023 paper reviewed 34 years of insect and plant data from across Europe to assess changes to phenology. Results from this research indicate that spring phenology in plants is advancing four times faster than insects, creating a dangerous mismatch.
While plants have been found to more consistently respond to warming, insects are another story. Their complex life cycles are responding differently, and the growing mismatch has a potential cascading effect across the complex food web on this planet.
An earlier spring may sound wonderful during an April cold snap or when protecting sensitive plants from risk of late frosts, but this changing phenology may have far-reaching impacts in the natural world. New research in this area is continually being published around the globe, providing important findings to watch as climate change unfolds in future decades.
Ryan Pankau is horticulture extension educator with University of Illinois Extension serving Champaign, Ford, Iroquois and Vermilion counties.
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