For Loblolly Pines, A Fertilization and Water Scarcity Paradox

Fertilized trees use water more efficiently, but may suffer the most in drought

by Stephanie Worley Firley
An exclusion structure allowed researchers to simulate a 30 percent rainfall reduction in the loblolly plots. Photo by Andy Laviner, Virginia Tech.

An exclusion structure allowed researchers to simulate a 30 percent rainfall reduction in the loblolly plots. Photo by Andy Laviner, Virginia Tech.

Driving down a country road or even an interstate highway in many areas of the South, one cannot help but notice them: the straight rows of pine trees, sometimes as far as the eye can see, that make up the 20 million acres of planted pines in the region. Eighty percent of these trees are loblolly pines, which even in plantations perform important ecological services such as storing carbon and filtering water. These forests also provide abundant wood to support local economies and provide 16 percent of industrial wood supplies of the entire globe.

As in natural forests, the growth of loblolly pines in plantations is limited by essential resources: sunlight, nutrients, and water. Fertilization — an increasingly common practice for adding nutrients to boost wood production — allows trees to shift their growth away from roots to leaves and stems. Since a tree is dependent on its roots to provide water, how does a fertilized tree respond when water supplies are limited in times of drought? Does increased productivity intensify water stress?

To explore these questions, university and U.S. Forest Service researchers experimented with fertilization treatments and simulated drought during a two-year study in a loblolly pine plantation located in central Virginia. Their findings were recently published in the journal Forest Ecology and Management.

The plantation was in its eighth growing season when the researchers began applying a fertilizer of essential nutrients in four study plots, while diverting rainfall away to simulate a drought of 30 percent  water reduction in four other plots. They also combined fertilization and drought simulation in four additional plots. Finally, they left four additional plots untouched to study as controls.

Despite the researchers’ best-laid plans, the plantation received unusually high amounts of precipitation during the study period. Even the plots that received 30 percent less water through rainfall diversion still received near historic amounts of precipitation. In the second year of study, the stems of fertilized trees were 21 percent larger than the control plot stems. However, in plots with diverted rainfall, stem growth was not reduced as expected, either with or without fertilization.  It is likely that the unusually wet conditions nullified the water diversion treatment impacts on stem growth.

But in addition to measuring stem growth, the researchers also continuously monitored environmental conditions and tree water use with a network of more than 100 automated sensors located in stands throughout the plantation. As expected, they observed a relative decrease in water use in the stands where rainfall was diverted (a 19 percent reduction in the second year of study). Contrary to their expectations, researchers also observed decreased water use in fertilized plots (a 13 percent decrease in the second study year), and concluded that fertilization could reduce water use almost as much as drought conditions. The greatest decrease in water use (29 percent) was seen in the stands with combined fertilization and rainfall diversion treatments.

Researchers say the cause of water use reductions associated with fertilization remains uncertain. “We suspect the reason may lie belowground, either in the number of roots or their ability to transport water,” says Eric Ward, a North Carolina State University scientist cooperating with the Eastern Forest Environmental Threat Assessment Center and the study’s lead author.

“In the short term, fertilized trees that achieve more wood production with less water could benefit both the world wood supply and the local water supply. However, if fertilization reduces the ability of roots to supply water to trees, we are concerned that vulnerability of plantations to severe drought will increase with fertilization,” says Ward.

This is especially a concern in the changing climate of the Southeast, where variable precipitation is expected to be the norm. If more trees die as a result of more frequent droughts, ecological services and forest products from these plantations could be damaged.

“We know that management of loblolly depends on the site and we expect our results to be site-specific as well,” says Ward, whose research team will continue to investigate the effects of fertilization over the coming year. “By understanding how trees move water from root to leaf, we hope that we can explain why fertilization might increase drought stress at some sites, but not others. This is the kind of research practicing foresters can use.”

This study is one of four identical experiments also being conducted in Georgia, Oklahoma, and Florida as part of the PINEMAP project. The next step is to begin integrating findings across this network of sites.

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For more information, email Eric Ward at

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Posted in Forest Landowners, Forest Products, Southern Pines

Guidelines for Regenerating Southern Pine Beetle Spots

by Zoё Hoyle, SRS Science Delivery Group


Composite photo showing southern pine beetle hot spot, damage to individual tree, and southern pine beetle. Photos by U.S. Forest Service, courtesy of

Composite photo showing southern pine beetle hot spot, damage to individual tree, and southern pine beetle. Photos by U.S. Forest Service, courtesy of

Guidelines for Regenerating Southern Pine Beetle Spots, a general technical report (GTR) by the Southern Research Station (SRS),  provides detailed guidance for regenerating pines in areas within forest stands where trees have been killed by southern pine beetle.

Authored by scientists from two units located in Pineville, Louisiana—the SRS Restoring and Managing Longleaf Pine Ecosystems unit and the SRS Insects, Diseases, and Invasive Plants unit—the GTR includes a key to help managers plan for regenerating spots within the context of the larger forest stand.

It’s hard to overestimate the economic and ecological importance of pine forests in the South, a region which is widely known as the Nation’s “wood basket.” The main pine species in the region are loblolly, slash, longleaf, and shortleaf. Loblolly pine, the most widely distributed and most commercially important tree species in the South, is vulnerable to infestations of southern pine beetle, a native insect.

The southern pine beetle is the most destructive forest pest in the southern United States. The most recent outbreak of the native insect (1999-2003) caused over $1 billion in damages across five states. Unlike most native insects, southern pine beetle kills its host trees in clumps—called spots—where almost all the trees are killed.

When trees start dying from southern pine beetle, overstory gaps form quickly, affecting the structure and functions of the larger stand. Managers may need to intervene to stop these spots from spreading and to regenerate affected stands. With large gaps or a string of small gaps, they can use their usual techniques to regenerate the area, reducing susceptibility to future southern pine beetle infestation by planting at lower densities, planting more resistant species such as longleaf pine, and other activities.

Southern pine beetle damage to a stand. Photo by Erich Vallery, courtesy of Bugwood.

Small gaps, or spots, are more common than large ones and offer particular challenges to forest managers. Most regeneration methods are designed for the stand level, while spots represent only a small portion of the stand. Remaining trees at the edges of small spots compete with seedlings for light and nutrients, making pine regeneration difficult. Hardwoods will also start growing in the gaps and will outcompete young pine seedlings unless controlled.

How a manager responds to southern pine beetle spots depends on the goals they have for the stand in terms of timber production, management of game and nongame animal species, preservation of water resources, recreational use, and other factors.

The authors of the publication developed guidelines and a key to provide managers a suggested course of action to regenerate southern pine beetle spots in relation to their goals, stand conditions, and the nature of the insect infestation. Managers can use the key to identify the information needed to decide on a particular set of actions, or prescriptions. The key in turn leads to specific prescriptions to help forest managers meet their goals with both present and future stands.

Access the full text of the GTR.

For more information, email Mary Anne Sword Sayer at

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Posted in Insects and Diseases, Longleaf Pines, Restoration, Southern Pines

Intertribal Timber Council Scholarships Connect Students with Forest Service Scientists

by Patty Matteson, SRS Science Delivery
Kim Yazzie, Navajo Nation, presenting at the recent ITC Annual Timber Symposium. A student at Portland State University, Yazzie received an ITC research scholarship.

Kim Yazzie, Navajo Nation, presenting at the recent ITC Annual Timber Symposium. A student at Portland State University, Yazzie received an ITC research scholarship.

Climate change, groundwater, and air quality are just a few of the focus areas of the recipients of the Intertribal Timber Council (ITC) Native American Natural Resource Scholarships announced recently. Connecting these students with U.S. Forest Service Southern Research Station (SRS)  scientists is a goal of the continuing ITC-SRS partnership.

“These students are encouraged to reach out to our researchers, who can assist them with their research project development,” says Serra Hoagland, biological scientist with the SRS Eastern Forest Environmental Threat Assessment Center and co-point of contact for Tribal Relations for SRS. “I am sure both the students and our scientists will enjoy working together. This scholarship opportunity is a great way to uphold our federal trust responsibility with tribal communities by supporting the advancement of these American Indian students in natural resources fields of study,” says Hoagland.

SRS funds will provide each student with a $4,000 research scholarship and an additional $1,000 to offset the costs of presenting a research poster at the ITC Annual Timber Symposium at the Coquille Indian Reservation in North Bend, Oregon. More than 300 tribal forest managers, council members and resource manager along with federal, state and private groups from the United States and Canada will attend the symposium.

Scholarship recipients:

  • Grace BullTail, Crow Nation: Cornell University – Researching groundwater quality in oil and gas drilling around the Fort Berthold Reservation, North Dakota.
  • Cody Sifford, Navajo Nation: University of Washington – Developing an impact assessment of local air quality as a result of biomass burns.
  • Crystal Tully-Cordova, Navajo Nation: University of Utah – Studying stable isotopes in precipitation, surface, and ground waters: Recording the North American Monsoon in Arizona, New Mexico, and Utah.
  • Victoria Walsey – Yakima Nation: University of Kansas – Bridging knowledge systems to improve ecosystem management along the Yukon River: How indigenous peoples can prepare themselves for climate change.
  • Kim Yazzie, Navajo Nation: Portland State University – Examining aquifer recharge and watershed response to climate change in the Upper Umatilla River sub-basin using the Precipitation Runoff Modeling System.

For more information, email Serra Hoagland

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Posted in Threats