Tree - Triadica sebifera
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Chinese tallow tree is a small to medium-sized monoecious tree. The leaves
are alternate, simple, and net-veined. The petiole is long with two glands
on the upper side near the blade. The blade is rhombic-ovate, entire,
with an acuminate apex and a round to truncate base. Leaves of Chinese
tallow tree turn red in the fall, making it a popular ornamental. The
flowers are imperfect, with green sepals and no petals, and are produced
in a terminal spike. The staminate flowers are terminal in the spike and
the pistillate ones are near the base. The fruit is a three-locular capsule
with three seeds. The seeds are globose-flattened, 6-9 mm in diameter,
turn white with age, and often persist on the tree into winter.
Plants grow in abandoned fields, pastures, waste areas, and forests.
The species grows in a wide range of environmental conditions: wet to
dry and shade to full sun. It reproduces by seeds only, but one plant
can produce hundreds of seeds. The seeds seem to have a tremendous ability
to germinate under adverse conditions. The plant is a fast-growing tree,
hence its popularity as a shade tree ornamental.
The fast-growing habit, massive seed production, and great seed germinability
allow this species to invade areas occupied by natives. It can outcompete
most natives and soon displaces them. The plants seem not to be eaten
by livestock and thus dominate in pastures.
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"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 the tallow trees out.
He is also 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,"
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 of 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.