As the demand for renewable, forest-based resources increases, forest managers must pursue alternatives that not only provide consistent material for pulpwood and bioenergy feedstock, but also conserve the biodiversity and ecological vitality of the landscape.
Under the direction of Stephen F. Austin State University’s Dr. Chris Comer, professor of forest wildlife management in the Arthur Temple College of Forestry and Agriculture, graduate student Elizabeth Messick recently completed research that contributes to a growing body of academic work investigating the potential ecological effects of land cover change in the form of eucalyptus plantations.
Across the globe, eucalyptus plantations play an important role in meeting the demand for hardwood pulp used to make a wide array of products utilized on a daily basis. Eucalyptus plantations, however, are not common in the U.S. According to Messick, pursing a Master of Science in forestry, there were roughly 3,000 acres of eucalyptus plantations in Southwest Louisiana and Southeast Texas in 2013.
“In this case, eucalyptus plantations were viewed as a tool enabling companies to gain hardwood fiber from upland sites during times of the year when bottomland hardwood forests are too wet to access,” said Dr. Ben Wigley, vice president of forestry programs for the National Council for Air and Stream Improvement, Inc.
NCASI, the primary funding source for Messick’s research, is an independent, non-profit research institute focused on environmental and sustainability topics relevant to forest management and the manufacturing of forest products.
To investigate the potential implications of this landscape change, Messick compared the habitat assemblages of birds during breeding season, as well as the presence of arthropods and stand structure in one-year-old eucalyptus and slash pine plantations located in Southwest Louisiana. Arthropods, invertebrate animals such as insects or spiders, are a key food source for many bird species.
“Birds themselves make up such a wide range of species and make pretty good indicators of biodiversity and change,” Messick said. “They’ll respond to vegetation change quickly, and they are a really good indicator species in that way.”
Because eucalyptus grows in height so rapidly, Messick also incorporated observations in six-year-old slash pine plantations to effectively compare the avian and arthropod composition in forest understory conditions comparable to that of two-year eucalyptus growth.
“The first year the eucalyptus were about seven to eight feet tall, and the second year they were almost 12 feet tall,” she said.
She said that following fertilization, the three-year-old eucalyptus stands have now reached approximately 30 feet in height.
Because of this rapid growth, eucalyptus plantations are entirely harvested after six to eight years, compared to pine forests, which are partially harvested for pulp around 12 to 15 years of age. The remaining pine trees are then allowed to grow to the size required for saw timber, which is harvested at 25 to 30 years of age.
Messick explained that a number of bird species utilize forests during different stages of forest succession, or growth. Although the successional periods within a eucalyptus forest may be shorter than that of pine, providing less time for habitat-specific birds to utilize a preferred growth stage, she said there also is a considerably shorter time between harvest and the reemergence of the species’ desired forest composition.
Based on two years of research, Messick found no statistically significant difference between the populations of arthropods and birds in the eucalyptus and pine plantations.
“The eucalyptus plantations themselves, at least in the first two years, don’t seem to be having a biological impact or an adverse impact on birds or arthropods,” she said.
As with many scientific studies, Messick said that continued monitoring is ideal to ensure that no future changes in biodiversity occur.
Although eucalyptus’ swift production of biomass makes it an attractive alternative to pine, Wigley said that residents should not expect a change in the region’s iconic pine tree landscape.
“I think there are opportunities in select locations to grow eucalyptus to meet special needs in certain situations,” he said.
Now, thanks to Messick’s research, managers have a better understanding of the sustainability and impacts of this option.
Left: An immature painted bunting perches in a eucalyptus tree during one of Messick's surveys. Right: Messick surveys the landscape in a young pine plantation.