From 1852 to 1858, Henry David Thoreau kept records of the flowering dates of more than 500 species of plants near his home in Concord, Mass. Twenty years later, the amateur botanist Alfred Hosmer began recording first flowering dates (FFD) for more than 700 species around Concord. His records were for the year 1878 and then from 1888 to 1902, a total of 16 years.
            Two biologists at Boston University took up the task in 2004 to see what effects climate change have had on flowering dates of 43 common species that had been observed by Thoreau and Hosmer. Abraham J. Miller-Rushing and Richard B. Primack noted that from 1852 to 2006, Concord warmed by 2.4 degrees C because of urbanization and global warming. They determined that plants are flowering seven days earlier on average than they did in Thoreau’s time. But some plants are flowering much earlier. Highbush blueberry, Vaccinum corymbosum, flowers 21 days earlier and yellow wood sorrel, Oxalis europaea, flowers 32 days earlier than they did 150 years ago.
     The researchers noted that earlier flowering times were strongly correlated with warming mean monthly temperatures in January, April and May over that time period. No plants flowered later with the warmer temperatures. (Ecology, February 2008)