How do scientists know spring flowers are blooming much earlier than they did years ago? By looking at meticulous records kept by American naturalists Henry David Thoreau and Wisconsin's own Aldo Leopold.
In a study published Wednesday, researchers from Boston and Harvard Universities and UW-Madison said some species are blooming almost a full month earlier.
The research was disclosed in a UW-Madison news release.
"In 2012, the warmest spring on record in Wisconsin, plants bloomed on average nearly a month earlier than they did just 67 years earlier, when Leopold made his last entry in his records," the release said.
The study used Thoreau's records of 32 native plant species in Concord, Mass., gathered between 1852 and 1858, and data of flowering times for 23 species in southern Wisconsin compiled by Leopold, between 1935 and 1945.
"These historical records provide a snapshot in time and a baseline of sorts, against which we can compare more recent records from the period in which climate change has accelerated," said Stan Temple, co-author of the study and professor emeritus of wildlife ecology at UW-Madison.
Two examples of early blooming today when matched up against the naturalists' work show the dramatic differences in this age of global warming.
Leopold observed the black cherry tree blooming in southern Wisconsin in 1942, noting the first blooms on May 31, when the mean temperature was 48 degrees.
In 2012, the mean spring temperature in southern Wisconsin was 54 degrees, and black cherry trees were blooming as early as May 6.
Leopold also observed bloodroot blooming on April 12 in 1942, when the same wildflower started blooming on March 17 in 2012.
The work has implications for predicting plant responses to changing climate, essential for plants such as fruit trees which are highly susceptible to the vagaries of climate and weather.
"Earlier blooming exposes plants to a greater risk of experiencing cold snaps that can damage blossoms and prevent fruiting," Temple said.
Door County's cherry crop was ruined in 2012 when trees bloomed very early because of record-breaking warmth followed by a frost.