Seasonal Cycles: Budburst

There are perhaps no signals of spring’s arrival more welcome than the blooming of flowers and leafing of trees. Thoreau spent countless hours recording when these events happened for individual species. The timing of when plants flower and leaf out in the spring is closely tied to temperature. In years when the average temperature in March, April, and May is warmer, flowers bloom and leaves come out earlier than in colder years. Over time, as the average temperature in Concord has increased, spring has been arriving earlier.

Plants in Concord are responding to warming temperatures by flowering two days earlier for each increase in temperature of 1°F. When Thoreau was recording flowering dates, the average spring temperature was 42°F and the average date of first flowering of 32 selected species was May 15. In recent years (2004-2012), the average spring temperature has been six degrees warmer at 48°F and the average date of first flowering of those same 32 species is eleven days earlier on May 4. A similar trend is seen with leaves now emerging earlier in the spring than in Thoreau’s time.

Students from the Concord-Carlisle High School Environmental Field Studies Group have been tracking the seasonal changes of about twenty trees annually.

Students from the Concord-Carlisle High School Environmental Field Studies Group have been tracking the seasonal changes of about twenty trees annually.

Richard Primack researching in concord

Inspired by Henry Thoreau’s records of seasonal events, Richard Primack has been carrying out research in Concord and other Massachusetts sites since 2003.

Lysimachia stricta and Lysimachia quadrifolia

Both Henry Thoreau and his sister Sophia used plant presses to prepare herbarium specimens. The two specimens on this sheet prepared by Sophia are Lysimachia stricta and Lysimachia quadrifolia.

To Learn More

Listen to the sounds of spring that one might hear at Walden Pond.

Read about “Record-breaking Early Flowering in the Eastern United States,” in PlosOne, 2013

Learn more about the stories your plants can tell at Project Budburst.

Background photo credit: Cherrie Corey
Photo/soundscape credits: Courtesy CCHS Environmental Field Studies Group; courtesy Richard Primack; David Bohl; Kezia Simister