Build on Our Legacy of Caring for the Land and Serving People
For 112 years, the U.S. Forest Service has improved landscapes and lives through research. The Nation’s forests are the source of tremendous social, ecological, and economic benefits, and research is vital to maintaining these benefits for future generations of Americans. This month, we feature a scientist, research, facilities and a partnership that are building on the Forest Service’s legacy of caring for the land and serving people.
Soils have so many values. Visit the Soil Science Society of America’s website to find a collection of soil-related education resources, all developed to support the UN’s International Year of Soils in 2015.
Jerry Van Sambeek
When he was in high school, Jerry Van Sambeek tried to grow his own black walnut seedlings from a bag of black walnuts relatives had given him. He wanted to plant the seedlings in his family’s fruit tree orchard. “Little did I know that I was making one of the mistakes I would be telling others to avoid during most of my research career,” said Van Sambeek, now a plant physiologist with the Northern Research Station. (Air-dried nuts intended for eating will not sprout.)
Van Sambeek has spent much of his career with the U.S. Forest Service examining the factors affecting propagation and growth of hardwoods. Many hardwood species are valued for their wood, which is used in furniture making, paneling and veneers , and for their wildlife value, which includes providing food for squirrels and white-tail deer. His research has ranged from studying the effects of stress on hardwood seedlings, to the profitable growth of black walnut trees in plantations, to the development of tissue culture techniques for white ash that can be used for propagating the species. “It’s a shame that emerald ash borer may possibly eliminate white ash before we can use the technology,” said Van Sambeek.
Today Van Sambeek is investigating ways to integrate cover crops into hardwood plantings to improve tree growth and soil health, and create habitat for pollinators. “There are not many databases that consider how competitive cover crop species are with the trees, how cover crops tolerate flood and shade, and how to manage trees, especially nut producing trees, in a woodland setting,” he said.
Communicating to land managers about what he has learned through his research is a passion for Van Sambeek. He leads many field tours demonstrating the effectiveness of different vegetation management practices and is an active participant in the Walnut Council, Northern Nut Tree Growers, Missouri Nut Growers Association, and the Association for Temperate Agroforestry.
Van Sambeek grew up on a dairy farm in the Midwest and during the summers he spent much of his time on a tractor working the crop and hay fields. “I am still an avid gardener and my interest in managing hardwood research plots has never waned over my 40 year career,” he said.
Rhizotron and Mesocosm
Restoring the nation’s forests and grasslands is rooted in soil, a vital if often overlooked factor in forest ecosystems. The Northern Research Station’s lab in Houghton, Mich., is equipped to study the fascinating world of below-ground with both a rhizotron (from “rhiza,” the Greek word for “root”) and a mesocosm (the scientific term for a larger, typically outdoor, isolated experimental unit under controlled conditions—think very big pots).
Built in 2005, the rhizotron is a tunnel-like structure that gives scientists 24 windows on the world of soil. Twelve of those windows give a view below the surrounding mature northern Michigan forest of sugar maple, oak, ash and basswood trees. The view is different on the other side of the tunnel’s hallway, where scientists installed sandy soil and a pine plantation that offer insight into how the soil beneath a highly manipulated forest system operates. Time-lapse cameras snap an image every 30 minutes both below ground and above ground, which allows scientists to relate soil activity with what happens in the forests above.
One example of the connection between the soil and the surface is the activity of symbiotic fungi, called mycorrhizas (“myco” means fungus, “rhiza” means root) which includes species of fungi that feed on sugar provided by tree roots in exchange for feeding essential nutrients to trees. Research based at the rhizotron has revealed that these fungi grow all year long, even under the deep northern snowpack, but grow more quickly when temperatures are warmer, with one exception. “For trees, late spring and early summer is a period of tremendous growth as leaves expand and trees add wood to support new leaves,” said Erik Lilleskov, a research ecologist based in Houghton. “The growth of symbiotic fungi slows dramatically during this period because trees are using virtually all of the sugars they produce, leaving much less sugar available for fungi.”
While the rhizotron is about actual forest conditions, the mesocosm is about controlled experiments. Twenty-four containers, all 1 meter cubed in size with one glass side, are arranged in an underground room while above ground, the plants growing in the containers are open to the environment. Scientists use the mesocosm to study the effects of change (drought, flooding, and temperature changes, for example) on the environment. In PEATcosm, a recently concluded experiment, scientists transplanted bogs in the 24 containers so scientists could understand how climate change might affect the ability of peatland to store carbon.
“How soil responds to climate change and invasive species invasions and other events matters tremendously to the resilience and productivity of forests,” Lilleskov said. “The rhizotron and mesocosm are letting us both observe and experiment with soil systems.”
Forest Floor and Carbon Counts
Since 2001, the USDA Forest Service’s Forest Inventory and Analysis program has been consistently measuring forest floor and soil attributes on permanent sample plots across all forest land and ownerships as part of the national forest inventory. Last year, the data were harmonized with auxiliary soils, climate, and geospatial data to develop models for predicting decaying leaves, branches and other organic material on the forest floor (“litter” in forestry terminology) and soil carbon stocks on forest land in the United States. These models were also used in reports generated for the United Nations Framework Convention on Climate Change (UNFCCC).
Forest ecosystems are the largest terrestrial carbon sink on earth, with much of the stored carbon moving from trees to the soil via the decomposition of litter. Estimating how much carbon is stored in the forest floor and soil is a complicated endeavor because the amount of carbon can vary between forest types on the same soils and across depths and over short distances.
“Thanks to the continuous investment in the comprehensive annual inventory of forests in the United States, we were able to develop a new modeling framework for predicting litter and soil carbon stocks and stock changes,” said Grant Domke, a research forester and team leader with the Northern Research Station. “The new framework better characterizes litter carbon stocks because it is site-specific and sensitive not only to changes in vegetation, but also to major drivers of litter accumulation and decomposition in forest ecosystems: temperature and precipitation.”
Research by Northern Research Station scientists resulted in an estimated 44 percent reduction in litter carbon stocks and an estimated 40 percent increase in soil carbon stocks relative to previous estimates in UNFCCC reporting. More broadly, this work suggests that Intergovernmental Panel on Climate Change defaults and country-specific models used to estimate litter and soil carbon in temperate forest ecosystems may not well represent the contribution of these pools in national carbon budgets.
“Learning more about the ecological processes driving carbon accumulation, sequestration, and emissions in forest ecosystems will allow us to continue to improve upon our estimates of forest carbon stocks and stock changes as well as better quantify the uncertainty associated with our estimates,” said Domke.
Ailanthus altissima, commonly known as tree-of-heaven, is an aggressive invasive tree species that has been in North America for more than 200 years. Originally colonizing disturbed sites such as roadsides, in the past 60 years it has begun to move into rural forests. Ailanthus has the potential to replace oak and other native tree species within Eastern hardwood forests. Scientists like U.S. Forest Service Plant Physiologist Joanne Rebbeck and her partners are working to keep that from happening.
Working with various agencies in the state of Ohio and the U.S. Forest Service’s Wayne National Forest, Rebbeck looked at the effects of prescribed fire, timber harvesting and landscape features on the distribution of Ailanthus. The information gathered in the study can help in development of management practices to reduce Ailanthus growth and spread. “Partners were essential to the implementation of this research as well as the delivery of science findings to the management community,” said Rebbeck.
Multiple partners from Ohio Department of Natural Resources, Division of Forestry and Division of Wildlife provided land resources to conduct research. They provided researchers with complete access to the Tar Hollow State Forest for installing long-term research plots, performed prescribed burns and opened their timber harvest records. Staff and resources from the Wayne National Forest and state agencies in Ohio enabled scientists to conduct helicopter mapping of Ailanthus. The Wayne National Forest supported testing of herbicide treatments on Ailanthus to determine their effectiveness in killing Ailanthus stems.
At the conclusion of the study, scientists and partners sponsored an Ailanthus-Fire Workshop that highlighted research and management recommendations based on study results. Management recommendations to curtail Ailanthus spread are currently being tested in cooperation with partners. Proven recommendations have been incorporated into the Northern Research Station’s SILVAH: OAK decision support system and training curricula.
The partnership continues to grow. Scientists and partners are now working together to study alternative methods to control Ailanthus using a native fungus that selectively kills the tree species. “These partnerships build a trusting and welcoming environment that engages managers to actively collaborate in active research programs,” said Rebbeck. “In turn, managers enhance research by providing their knowledge and perspectives.”