Reining in Loosestrife
Professor of Biology George Ellmore and biology research
student Lauren Griffen inspect roadside loosestrife.
Photographers, tourists and hikers may sing the praises of the
purple loosestrife, a tall, vivid weed frequently seen along roadsides
and wetlands. But wildlife experts know it as an invading menace.
Brought to this country from Europe in ship ballast, probably in
the late 1700s, the plant has pushed out natural plants whose seeds
provide food for fish and wildlife and whose foliage makes nesting
places. Not only is the plant tenacious--a woody pillow at the base
makes it extremely difficult to uproot--but each one is capable
of producing nearly three million seeds a year, seeds that can still
sprout several years hence and are easily spread by water.
Now George Ellmore, associate professor of biology, and biology
research student Lauren Griffen, a senior, have devised a way they
believe can help drastically slow the growth of purple loosestrife.
Working at the Hummingbird Cay Field Station in the Bahamas, Griffen
and other students have used the extended growing season to study
seed germination. Visiting Hummingbird Cay each March, Ellmore and
his students are able to test seeds at soil temperatures that won't
be reached in New England until mid-summer.
"We asked, how might warm temperatures be used to restrict
germination of loose-strife?" Ellmore explained. "In the
lab, we found that constant temperatures above about 130 degrees
Fahrenheit were lethal, even when experienced for as little as three
hours per day."
The next question was whether that temperature could be achieved
outside to actually kill the seeds by heating them up. The team
used the sun to overheat the soil, a process called solarization.
They put clear plastic over the wetland soil and kept a continuous
record of the temperature, using data loggers supplied by J. Michael
Reed, assistant professor of biology. The plastic acted as a greenhouse
and elevated the temperature for about eight hours a day.
The result: The seeds died. Heat-retentive plastics are used in
agriculture in certain parts of the world, Ellmore said, so the
process is not a new one. Plastic can be set down over a quarter
acre of land at a time.
But, said Ellmore, the Tufts study is the first evidence that loosestrife
seeds can be killed while still in wetland soil. One approach with
solarization could be to have wetlands managers draw down the wetlands
to mud, cover the soil with plastic for a week, then restore the
water. Another would be to put plastic down over the plants themselves
before they sprout.
"We're not suggesting this as a way to stop an established
population of loosestrife," Ellmore said. "Instead, solarization
can prevent a new population from getting established, or can be
used to make older populations more vulnerable to plant-removal
programs by depleting seed banks."