Flowering Time

Last year we noted the first flowers of spring on March 30 - Draba of course - and a couple of weeks later (April 13) Devil’s gate twinpod showed its first flower. This year, those two species were again the first to bloom, both just about one month later than last spring.

As a lead-in to the topic of plant response to climate change, this seems like a non-starter, doesn’t it? But, whether the spring is cold or hot, plants must leaf-out and flower at the “best” time. How do they know when that is?

Timing is everything

Because timing is so important to plants, they have evolved complex ways to get the timing right. Many require warm temperatures over a certain length of time before they start to respond. They can, in effect, add up the number of warm hours or days to reach a threshold, then genes are turned on that lead to growth, leaf development or flower buds. In this way, they avoid budding during an early warm spell. Plants may also use soil moisture and day length as cues to when changes ought to occur.

In the past, naturalists and amateurs often kept track of the dates of flowering, leaf-out and other events, often to assist in making predictions that would be useful to farmers, ranchers, and others who make a living outdoors. Now that our lifestyles keep us indoors, fewer people keep these kinds of records. However, climate change scientists have found some of these old records to be extremely valuable to show how plants respond to a warming environment.

For example, Henry David Thoreau, author of Walden, kept extensive records on leafing and flowering dates for plants around his Concord, MA, home during the years 1852-1858. Toward the end of the 19th century, Alfred Hosmer, a shopkeeper, kept records of 700 plant species around Concord. Later yet, 1963-1993, Pennie Logemann, a landscape architect, kept records on 250 plant species around her home in Concord.

Most recently, the area has been revisited by Boston University botanists Richard Primack and colleagues. They compared their flowering dates with those of the earlier Concordians, and found a significant shift to earlier flowering dates.

 

They also showed that the change in flowering date is strongly correlated with an increase in mean spring temperature.

What this means, is that we can expect flowers and leaves to appear earlier and earlier as the earth continues to warm, despite unusually late springs like this one. It also shows how well adapted plants are to variable weather. As those of us who live here know, the only predicable thing about Wyoming weather is its unpredictability! 

Written by Dorothy Tuthill, Biodiversity Institute

Reference

E. R. Ellwood, S. A. Temple, R. B. Primack, N. L. Bradley, and C. C. Davis. 2013. Record-breaking early flowering in the eastern United States. PLoS ONE 8(1): e53788. doi:10.1371/journal.pone.0053788