A new study has determined that some of the world's most beloved species of flowers like lilies, orchids, violets, roses, and dogwoods have also been hit by global warming.
The study, by scientists at Harvard University, US, have found that different plant families near Walden Pond in Concord, Massachusetts, have borne the effects of climate change in strikingly different ways.
Over the past 150 years, some of the plants in Thoreau's woods have shifted their flowering time by as much as three weeks as spring temperatures have risen, the researchers say, while others have been less flexible.
Many plant families that have proven unable to adjust their flowering time have experienced sharp declines or even elimination from the local landscape.
"It had been thought that climate change would result in uniform shifts across plant species, but our work shows that plant species do not respond to climate change uniformly or randomly," said Charles C. Davis, assistant professor of organismic and evolutionary biology in Harvard's Faculty of Arts and Sciences.
"Some plants around Walden Pond have been quite resilient in the face of climate change, while others have fared far worse. Closely related species that are not able to adjust their flowering times in the face of rising temperatures are decreasing in abundance," he added.
Some 27 percent of all species Thoreau recorded in the mid-19th century are now locally extinct, and another 36 percent are so sparse that extinction may be imminent.
Plant families that have been especially hard-hit by global warming have included lilies, orchids, buttercups, violets, roses, dogwoods, and mints.
Many of the gainers have been weedier mustards and knotweeds, along with various non-native species.
"The species harmed by climate change are among the most charismatic found in the New England landscape," Davis said.
According to Davis, "The plants in our survey now flower, on average, one week earlier in the spring than their ancestors did in Thoreau's time."
"However, there is wide variation among plant families. Some have shown no shift in flowering at all, while others now bloom 16 to 20 days earlier in the spring," he added.
As mean annual temperatures increase, plants can adjust their growth patterns in several ways.
For example, forests shift toward the poles, alpine tree lines move up mountains to higher altitudes, and flowering time can shift.
During eras of climate change, plants that cannot adjust their flowering schedule - and thus flower at sub-optimal times - may experience dramatic declines in population size and local extinction.