Ecologist exploring peskiness of tallow tree

Ecologist
exploring peskiness of tallow tree
…………………………………………………………………

BY B.J. ALMOND
Rice News Staff

The Chinese tallow tree has been turning Gulf Coast grasslands
into single-species forests, and Rice University ecologist
Evan Siemann hopes to find out how this tree has been able
to “break all the rules.”

“The incredible
diversity of native plants in the coastal prairies is gone
within 30 years after the Chinese tallow tree invades the
area,” said Siemann, assistant professor of ecology
and evolutionary biology. “By studying how this tree
has been able to thrive, we should be able to learn more
about the rules that govern a biological community and the
interactions among species within that community.”

Known for its
heart-shaped leaves and white fruits, the Chinese tallow
tree originated in Asia. The U.S. government brought it
to the Gulf Coast area around 1900 in hope of using the
wax-covered seeds as an agricultural crop. That project
was unsuccessful, and the trees escaped from cultivation.

Siemann is concerned
about the spread of Chinese tallow trees, because once they
replace bluestem grasses, sunflowers, blazing stars and
other plants found in the prairies, those species and their
associated animal fauna will not come back.
One of the reasons this tree has been able to grow so well
is that insects have left it alone and munched on other
foliage. Siemann said this is particularly peculiar because
unlike the slow-growing tallow tree found in China, the
American variety lets its defenses down. The Chinese variety
has chemicals in its leaves that makes them hard to digest.
The American variety does not produce this substance; instead,
it appears to use that energy to grow quickly, which promotes
the development of forests.

Siemann is testing
various methods of controlling the tallow trees using land
in Galveston County owned by the University of Houston Coastal
Center. “If you knock down the tallow trees, they just
sprout from roots like crazy,” he said. But fire can
kill small tallow trees when they’re vulnerable. During
a six-year experiment, Siemann is studying how frequently
a prairie needs to be burned to keep out the tallow trees.

He also is flooding
sections of prairies and pumping water out of others to
determine whether wet or dry conditions can make the prairies
more vulnerable to invasion. Another study involves examining
the effect fertilizing with nitrogen has on the trees’
growth. “Prairie grass is very efficient at using nitrogen,
and the tallow tree uses nitrogen very inefficiently,”
Siemann said.

Because the
Chinese tallow trees are starting to sprout in the forests
of East Texas, Siemann believes the lessons learned from
his research will be applicable to many areas. “This
tree is gobbling up real estate everywhere,” he said.
“Once the canopy trees come down, they’ll be replaced
by Chinese tallow trees.” Several experiments in the
Big Thicket National Preserve investigate whether the same
factors are responsible for the Chinese tallow tree’s
success in the forests as in grasslands.

Siemann and
William Rogers, the Huxley Instructor in Ecology and Evolutionary
Biology at Rice, have grants from the Environmental Protection
Agency, the National Park Service and the National Science
Foundation to study the biology of Chinese tallow trees
and methods of controlling it.

Photos and more
information about Siemann’s work can be found at <www.ruf.rice.edu/~siemann>.