Tuesday, May 21, 2013

Spring has finally sprung in Chicago! But is it as late as it seems?

Trout lilies, Trillium and Mayapples in the woods at Chicago Botanic Garden

Trout lilies, Trillium and Mayapples
in the woods at Chicago Botanic Garden; 
Photo courtesy of Kay Havens
I had the pleasure of walking through the Mary Mix McDonald Woods at Chicago Botanic Garden this week to enjoy the amazing display of spring wildflowers. This year, it sure felt like spring was a long time coming. Especially compared to last year when it came remarkably early. I wondered how the spring wildflower timing compared to previous several years in the Chicago area. Thanks to Project BudBurst, I’m able to easily look back at my phenological observations and those of others in the region.

For instance, I’ve been tracking when the first Forsythia flower opens at Chicago Botanic Garden since 2007. The earliest bloom was last year on March 15, 2012; the latest first flower was this year on April 20, 2013. However in 2007 and 2008 we also had first flowers in mid-April (4/16/07 and 4/17/08), so as we look back in time, this year’s bloom time doesn’t feel quite so late. In the graph below we show the variation in flowering dates, using Julian dates which standardize for differences in dates between non-leap and leap years.

In the Chicago area, we have a wealth of phenology data collected by the authors of our local flora, Plants of the Chicago Region by Swink and Wilhelm (1994). While they were gathering data for their book, they recorded when they saw plants in bloom from the late 1950s to the early 1990s.  For instance, for Forsythia, they record its bloom period as April 25-May 5. So when we look a little further back in time, even this spring which seemed so late, is earlier than it has been in the past.  I took a similar look at several other species, both native and non-native, for which we have both Project BudBurst data and data from Swink and Wilhelm’s book. About 70% of the species have earlier flowering dates in the last 6 years compared to those recorded by Swink and Wilhelm. I show some of the species that have advanced their flowering dates in the table below.

Earliest First Flower Observations
Common name (Genus species)
Swink & Wilhelm 1950s-1990s
Project BudBurst
Days Advanced
Forsythia (Forsythia x intermedia)
April 25
March 15
Spiderwort (Tradescantia ohiensis)
May 14
April 12
Dogtooth violet (Erythronium americanum)
April 6
March 20
Red Maple (Acer rubrum)
March 20
March 6
Mayapple (Podophyllum peltatum)
May 1
April 17
Lilac (Syringa vulgaris)
May 3
March 20
Black locust (Robinia pseudoacacia)
May 9
April 20
Bradford pear (Pyrus calleryana)
April 15
April 13

Plant phenology, particularly when plants leaf out and bloom in the spring, is remarkably sensitive to the annual weather. Looking at phenological records over much longer periods of time can tell us a lot about how the climate is changing. Many scientists are comparing contemporary bloom times with historic bloom times recorded by naturalists like Aldo Leopold in the early 1900s and Henry David Thoreau in the mid-1800s, as well as records kept by farmers, gardeners and others interested in the natural world. Two of the longest phenological data sets are those maintained about cherry blossoms in Japan (dating back to 900 AD) and grape harvest dates by wine makers in Switzerland (dating back to 1480 AD). Plants have so much to tell us, if we take the time to listen!

Contributed by Dr. Kay Havens

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