In the Eastern US, spring flowers keep pace with warming climate
news.wisc.edu |
Using
the meticulous phenological records of two iconic American naturalists, Henry
David Thoreau and Aldo Leopold, scientists have demonstrated that native plants
in the eastern United States are flowering as much as a month earlier in
response to a warming climate. The new study is important because it gives
scientists a peek inside the black box of ecological change. The work may also
help predict effects on important agricultural crops, which depend on flowering
to produce fruit.
The study was published online Jan. 16 in PLoS One by a
team of researchers from Boston and Harvard Universities and the University of
Wisconsin-Madison.
Compared
to the timing of spring flowering in Thoreau's day, native plants such as
serviceberry and nodding trillium are blooming 11 days earlier, on average, in
the area around Concord, Mass., where Thoreau famously lived and worked. Nearly
a thousand miles away in Wisconsin, where Leopold gathered his records of
blooming plants like wild geranium and marsh marigold, the change is even more
striking. In 2012, the warmest spring on record for Wisconsin, plants bloomed
on average nearly a month earlier than they did just 67 years earlier when
Leopold made his last entry.
"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," explains Stan Temple, a co-author of the study
and an emeritus UW-Madison professor of wildlife ecology. Temple is also a
senior fellow at the Aldo Leopold Foundation in Baraboo, Wis., a stone's throw
from the iconic shack where Leopold made many of his observations.
Although
the new study is not the first to document the relationship between temperature
and flowering dates and the trend toward climate-driven early blooming, it is
the first to suggest that the trend in flowering plants may continue beyond
what has been observed in controlled studies. The work thus has important
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.
"We
used relationships revealed in historical records to predict how 47 species of
native plants would respond to unprecedented spring temperatures, but that has
only been possible because naturalists, past and present, kept good records of
what they observed in nature," Temple avers.
Importantly,
the results give scientists a peek into the subtleties of ecological change in
response to climate change. Flowering of native plants, a harbinger of spring
in the world's temperate regions, signals the start of the growing season.
Changes in the timing of flowering have broad implications for the animals and
insects that depend on the plants.
"Earlier
blooming exposes plants to a greater risk of experiencing cold snaps that can
damage blossoms and prevent fruiting," says Temple. "The Door County
(Wisconsin) cherry crop was ruined in 2012 because the trees bloomed very early
in response to record-breaking warmth only to be hit by subsequent frost."
"The
Door County cherry crop was ruined in 2012 because the trees bloomed very early
in response to record-breaking warmth only to be hit by subsequent frost."
The new
study keyed on the detailed phenological records of 32 native plant species in
Concord, Mass., kept between 1852 and 1858 by Thoreau, a pioneering naturalist
best known as the author of "Walden," as well as later records. A
second data set of flowering times for 23 species in southern Wisconsin was
compiled by Leopold, a renowned wildlife ecologist at the University of
Wisconsin and author of "A Sand County Almanac." Leopold and his
students gathered their data in Dane and Sauk Counties between 1935 and 1945.
From 1977 until she died in 2011, Aldo Leopold's daughter Nina Leopold Bradley
resumed the collection of phenological records near the Leopold Shack.
"Both
Thoreau and Leopold were part of the 19th century naturalist movement in which
individuals often kept meticulous daily journals recording the things they
observed in nature," notes Temple. "Most of those journals have been
lost over time, but Thoreau and Leopold were famous writers, and their journals
have been preserved, providing us with unparalleled historical data."
Comparing
modern observations with those gathered by Leopold shows that in 1942, when the
mean spring temperature in southern Wisconsin was 48 degrees Fahrenheit, black
cherry bloomed on May 31. In 2012, with a mean spring temperature of 54 degrees
Fahrenheit, black cherry blooms were observed as early as May 6. In 1942,
Leopold's notes show the woodland wildflower bloodroot blooming on April 12. In
2012, bloodroot was first observed blossoming March 17.
Together,
these two data sets provide a unique record of flowering trends in the eastern
United States over a 161-year period, says Temple.
"Leopold
and Thoreau had no idea their observations would help us understand responses
to human-caused climate change," says Temple. "But Leopold knew his
records might be useful in retrospect when he wrote: 'Keeping records enhances
the pleasure of the search, and the chance of finding order and meaning in
these events.'"
Source: University
of Wisconsin-Madison
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