Global climate change, changes in forest management practices, and changes in pollutants in the atmosphere will all interact to alter forest productivity and return of plant litter (for example, leaf fall) to the forest floor over time. However, it is not known whether the amount of organic matter in soils will change in proportion to changes in litter inputs, or whether there might be non-linear interactions that may lead to disproportional soil changes. Understanding processes that increase or decrease soil organic matter is critical for understanding the global carbon balance, as carbon in soil organic matter amounts to more than the carbon stored in plant mass and in the atmosphere combined. The flux of carbon between soils and the atmosphere is also large, with the annual amount of carbon released from soils about 10 times that due to fossil fuel combustion. The DIRT (Detrital Inputs and Removal Treatments) experiment, started at the H.J. Andrews Experimental Forest in Oregon in 1997, is a long-term study where litter is manipulated either by increasing above-ground wood inputs, eliminating aboveground inputs, eliminating belowground (root) inputs, or eliminating both above- and belowground inputs. The experiment is designed to address such questions as: What controls the long-term storage of carbon in forest soils? What chemical and physical parts of SOM are most stable? Can added inputs increase soil carbon storage, or is maximum soil carbon storage more determined by climate and soil mineral makeup? Monitoring changes in carbon storage in the DIRT plots will generate a time course of carbon stabilization and loss under the different treatments.
Understanding the mechanisms that control soil carbon is vital not only to forest management, but also to the accurate prediction of feedbacks from forests to climate change. The DIRT experiment is unique to environmental science and uniquely suited to explore the role of litter quality and quantity in determining stabilization of soil carbon, a significant unknown in current ecosystem models. In this project, focus will also be placed on training of undergraduate Honors students, with results incorporated into a required Honors Ecology course at Oregon State University. The project will leverage the Long-Term Ecological Research program at the Andrews Forest for outreach to forest managers and the public. Both the project data and the sampled soils will be made freely available to researchers across the world. The long-term core data are already available on the Andrews Forest web site and the DIRT web site.
