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Chinese tallow growth negative for native bird species

Unfettered growth of Chinese tallow trees in the southeastern United States does not bode well for native bird species, Lamar University researchers say.

The findings are from research conducted in 2009 and 2010 that will soon be published in The Condor, the international journal of the Cooper Ornithological Society. Katy Gifford, who graduated Lamar with a M.S. degree in 2010, conducted the study that, under the direction of Jim Armacost, assistant professor of biology at Lamar, demonstrated the effects of the invasive plant species on native biodiversity.

Jim Armacost in the field.Armacost, who holds a Ph.D. in biology from Illinois State University, is a broadly trained naturalist with interests in ecology, natural history, biodiversity and conservation biology.

“Although invasive plant species negatively affect invaded ecosystems and diminish native biodiversity, they may provide food and other resources for some native birds,” Armacost said.

“What is not well documented is whether dense stands of Chinese tallow can adequately provide suitable habitat for many of the forest species of forest birds,” Armacost said. “We wanted to see if monotypic stands – that is, areas where the invasive Chinese tallow trees are dominant – are good habitat for native forest birds such as northern cardinals, Carolina chickadees, and Carolina wrens.”

Using six study plots in Jefferson and Hardin counties, Gifford, from Victoria, and Cody Conway, an undergraduate biology major from Orange who also graduated in 2010, used point counts to compare habitat use of forest birds in native mixed-species forest stands, mature tallow stands and young tallow stands.

The Chinese tallow plots were on private land, Armacost said, because governmental entities such as Texas Parks and Wildlife and the U.S. Fish and Wildlife Service have been more effective in controlling Chinese tallow growth.

Through their year-round observations the pair found mature tallow stands supported significantly fewer species of forest birds than native forest stands only during the spring migratory period, but bird population densities were similar in mature tallow and native forest stands throughout the year. However, young tallow stands supported significantly fewer species of forest birds than native forest stands in all seasons except for fall, and significantly lower bird population densities during the breeding season.

“While monotypic stands of Chinese tallow trees provide suitable habitat for some forest bird species, especially in winter, the preservation of native mixed-species forest stands is recommended to preserve overall forest bird diversity,” Armacost said.

Katy Gifford and Cody Conway“Invasive species pose the second-greatest threat to biodiversity of native species after habitat loss,” Armacost said. “Invasive species, by and large, have been introduced to new areas by humans, sometimes intentionally, sometimes unintentionally.”

Invasive species can have tremendous impacts in many other ways as well, prompting The Texas State University System to create the Institute for the Study of Invasive Species. The institute is the state’s first comprehensive research effort focused on the early detection and elimination of multiple invasive species. Housed at Sam Houston State University, the institute draws from the experience of more than 40 researchers within the university system.

The threat of invasive species is particularly keen in Texas. As a major transportation hub with many ports, Texas is a key point of origin for the nation’s new threats of invasive species.  The red fire ant, zebra mussel, giant salvinia, water hyacinth, Chinese tallow and Formosan termites are but a few invasive species to enter Texas. To date, more than 800 aquatic and terrestrial species have invaded Texas. The impact of these species is far-reaching, including threatening the nation’s food supply, damaging infrastructure, destroying natural resources and reducing water supplies.

“I am interested in further study to determine whether the paucity of breeding forest birds in young, dense Chinese tallow stands is due to a lack of suitable nesting sites or food resources. Few insect species feed on the tallow trees, so that limits food resources for insectivorous birds,” Armacost said.